BRIDGE DISASTERS IN AMERICA _The Cause and the Remedy_ BY GEORGE L. VOSE AUTHOR OF "MANUAL FOR RAILROAD ENGINEERS AND ENGINEERING STUDENTS, " "LIFE AND WORKS OF GEORGE W. WHISTLER, CIVIL ENGINEER, " ETC. _"ETERNAL VIGILANCE IS THE PRICE OF LIBERTY"_ BOSTON LEE AND SHEPARD PUBLISHERS 10 MILK STREET NEXT OLD SOUTH MEETING HOUSE 1887 NOTE. The substance of the following pages appeared originally in "TheRailroad Gazette. " It was afterwards reproduced in pamphlet form, andhas since been several times delivered as an address to variousbodies, the last occasion being before the Legislature ofMassachusetts, 1887. It is now re-published, with some new matteradded, in the hope that the public attention may be called to asubject which has so important a bearing upon the public safety. COPYRIGHT, 1887, BY LEE AND SHEPARD. _All rights reserved. _ BRIDGE DISASTERS IN AMERICA. Nearly all of the disasters which occur from the breaking down ofbridges are caused by defects which would be easily detected by anefficient system of inspection. Not less than forty bridges fall inthe United States every year. No system of public inspection orcontrol at present existing has been able to detect in advance thedefects in these structures, or to prevent the disasters. After adefective bridge falls, it is in nearly every case easy to see why itdid so. It would be just about as easy, in most cases, to tell inadvance that such a structure would fall if it ever happened to beheavily loaded. Hundreds of bridges are to-day standing in thiscountry simply because they never happen to have received the loadwhich is at any time liable to come upon them. A few years ago an iron highway bridge at Dixon, Ill. , fell, while acrowd was upon it, and killed sixty persons. The briefest inspectionof that bridge by any competent engineer would have been sure tocondemn it. A few years later the Ashtabula bridge upon the LakeShore Railroad broke down under an express train, and killed overeighty passengers. The report of the committee of the OhioLegislature appointed to investigate that disaster concluded, first, that the bridge went down under an ordinary load by reason ofdefects in its original construction; and, secondly, that the defectsin the original construction of the bridge could have been discoveredat any time after its erection by careful examination. Hardly had thepublic recovered from the shock of this terrible disaster when theTariffville calamity added its list of dead and wounded to the longroll already charged to the ignorance and recklessness whichcharacterize so much of the management of the public works in thiscountry. There are many bridges now in use upon our railroads in no way betterthan those at Ashtabula and Tariffville, and which await only theright combination of circumstances to tumble down. There are, by thelaws of chance, just so many persons who are going to be killed onthose bridges. There are hundreds of highway bridges now in dailyuse which are in no way safer than the bridge at Dixon was, and whichwould certainly be condemned by five minutes of competent and honestinspection. More than that, many of them have already been condemnedas unfit for public use, but yet are allowed to remain, and invitethe disaster which is sure to come. Can nothing be done to preventthis reckless and wicked waste of human life? Can we not have somesystem of public control of public works which shall secure thepublic safety? The answer to this question will be, Not until thepublic is a good deal more enlightened upon these matters than it isnow. It has been very correctly remarked, that, in order to bring adisaster to the public notice, it must be emphasized by loss oflife. The Ashtabula bridge fell, and killed over eighty persons; anda storm of indignation swept over the country, from one end to theother. No language was severe enough to apply to the managers of theLake Shore Railroad; but if that very bridge had fallen under afreight-train, and no one had been injured, the occurrence would havebeen dismissed with a paragraph, if, indeed, it had received eventhat recognition. In February, 1879, a span one hundred and ten feetlong of an iron bridge on the Chicago and Alton Railroad atWilmington fell as a train of empty coal-cars was passing over it, and three cars were precipitated into the river, a distance of overthirty feet. No one was injured. Not a word of comment was ever madein regard to this occurrence. Suppose, that, in place of emptycoal-cars, the train had consisted of loaded passenger-cars, andthat one hundred persons had been killed. We know very well what theresult would have been. Is not the company just as much to blame inone case as the other? On the night of the 8th of November, 1879, onespan of the large bridge over the Missouri at St. Charles gave way asa freight-train was crossing it, and seventeen loaded stock-cars fella distance of eighty feet into the river. Two brakemen and twodrovers were killed. This bridge, says the only account that appearedin the papers, did not break apparently, for the whole span "wentdown" with the cars upon it. It could hardly make much difference tothe four men who were killed, whether the bridge broke down, or"went" down. Not a word of comment was ever made in the papersoutside of Missouri in regard to this disaster. Suppose, that, inplace of seventeen stock-cars, half a dozen passenger-cars had fallenfrom a height of eighty feet into the river, and that, in place ofkilling two brakemen and two drovers, two or three hundred passengershad been killed. Is not the public just as much concerned in one caseas in the other? Suppose that a bridge now standing is exactly as unsafe as theAshtabula bridge was the day before it fell, would it be possible toawaken public attention enough to have it examined? Probably not. About two years ago an attempt was made to induce one of the leadingdailies in this country to expose a wretchedly unsafe bridge in NewEngland. The editor declined, on the ground that the matter was notof sufficient interest for his readers; but less than a monthafterwards he devoted three columns of his paper to a detailedaccount of a bridge disaster in Scotland, and asked why it was thatsuch things must happen, and if there was no way of determining inadvance whether a bridge was safe, or not? This editor certainly would not maintain, that, in itself, it wasmore important to describe a disaster after it had occurred than toendeavor to prevent the occurrence; but, as a business man, he knewperfectly well that his patrons would read an account giving all ofthe sickening detail of a terrible catastrophe, while few, if any, would wade through a dry discussion of the means for protecting thepublic from just such disasters. The public is always very indignantwith the effect, but does not care to trouble itself with the cause;but the effect never will be prevented until the cause iscontrolled; and the sooner the public understands that the cause isin its own hands, to be controlled, or not, as it chooses, the soonerwe shall have a remedy for the fearful disasters which are altogethertoo common in the United States. In a country where government controls all matters on which thepublic safety depends, and where no bridge over which the public isto pass is allowed to be built except after the plans have beenapproved by competent authority, where no work can be executed exceptunder the rigid inspection of the best experts, nor opened to thepublic until it has been officially tested and accepted, it makeslittle or no difference whether the public is informed, or not, uponthese matters; but in a country like the United States, where any manmay at any time open a shop for the manufacture of bridges, whetherhe knows any thing about the business, or not, and is at liberty touse cheap and insufficient material, and where public officers arealways to be found ready to buy such bridges, simply because thefirst cost is low, and to place them in the public ways, it makes agood deal of difference. There is at present in this countryabsolutely no law, no control, no inspection, which can prevent thebuilding and the use of unsafe bridges; and there never will be untilthe people who make the laws see the need of such control. There is no one thing more important in this matter than that weshould be able to fix precisely the blame in case of disaster uponsome person to whom the proper punishment may be applied. If everyrailway director, or town or county officer, knew that he was heldpersonally accountable for the failure of any bridge in his charge, we should soon have a decided improvement in these structures. If wecould show that a certain bridge in a large town had been for a longtime old, rotten, worn out, and liable at any moment to tumble down, and could show in addition, that the public officers having charge ofsuch a bridge knew this to be the case, and still allowed the publicto pass over it, we can see at once, that, in case of disaster, theblame would be clearly located, and the action for damages would beshort and decisive. Once let a town have heavy damages to pay, andlet it know at the same time that the town officers are clearlyaccountable for the loss, and it is possible that it would be willingto adopt some system that should prevent the recurrence of such anoutlay. To see what may be accomplished by an efficient system of publicinspection, it is necessary to know something in regard to thestructures to be inspected. We have now in common use in thiscountry, both upon our roads and our railroads, bridges made entirelyof iron, bridges of wood and iron combined, and occasionally, thoughnot often nowadays, a bridge entirely of wood; and these structuresare to be seen of a great variety of patterns, of all sizes, and inevery stage of preservation. Of late so great has been the demand forbridge-work, that this branch of engineering has become a trade byitself; and we find immense works fitted up with an endless varietyof the most admirably adapted machine-tools devoted exclusively tothe making of bridges of wood, iron, steel, or all combined. As inall division of labor, the result of this specialization has been toimprove the quality of the product, to lessen the cost, and toincrease the demand, until many of our large firms reckon the lengthof bridging which they have erected by miles instead of feet. Asusual, however, in such cases, unprincipled adventurers are notwanting, who, taking advantage of a great demand, do not hesitate tofit up cheap shops, to buy poor material, and to flood the marketwith a class of bridges made with a single object in view, viz. , tosell, relying upon the ignorance--or something worse--of publicofficials for custom. Not a year passes in which some of thesewretched traps do not tumble down, and cause a greater or less lossof life, and at the same time, with uninformed people, throwdiscredit on the whole modern system of bridge-building. This evilaffects particularly highway bridges. The ordinary countycommissioner or selectman considers himself amply competent tocontract for a bridge of wood or iron, though he may never have givena single day of thought to the matter before his appointment tooffice. The result is, that we see all over the country a greatnumber of highway bridges which have been sold by dishonest buildersto ignorant officials, and which are on the eve of falling, and awaitonly an extra large crowd of people, a company of soldiers, aprocession, or something of the sort, to break down. Not many years ago, a new highway bridge of iron was to be made overone of the principal rivers in New England. The county commissionersdesired a well-known engineer, especially noted as a bridge-builder, to superintend the work, in order to see that it was properlyexecuted. The engineer, after inspection of the plans, told thecommissioners plainly that the design was defective, and would notmake a safe bridge; and that, unless it was materially changed, hewould have nothing to do with it. The bridge, however, was a cheapone, and, as such, commended itself to the commissioners, whoproceeded to have it erected according to the original plan; andthese same commissioners now point to that bridge, which has not yetfallen, but which is liable to do so at any time, as a completevindication of their judgment, so called, as opposed to that of theengineer who had spent his life in building bridges. An impression exists in the minds of many persons, that it is purelya matter of opinion whether a bridge is safe, or not. In very manycases, however, --perhaps in most, --it is not at all a matter ofopinion, but a matter of fact and of arithmetic. The whole questionalways comes to this: Is the material in this bridge of good quality?Is there enough of it? Is it correctly disposed, and properly puttogether? With given dimensions, and knowing the load to be carried, it is a matter of the very simplest computation to fix the size ofeach member. We know what one square inch of iron will hold, and weknow, also, the total number of pounds to be sustained; and it is nomatter of opinion, but one of simple division, how many times onewill go into the other. But it may be asked, Can the precise load which is coming upon anystructure be exactly fixed? are not the circumstances under whichbridges are loaded very different? Bridges in different localitiesare certainly subjected to very different loads, and under verydifferent conditions; but the proper loads to be provided for havebeen fixed by the best authority for all cases within narrow enoughlimits for all practical purposes. Few persons are aware of theweight of a closely packed crowd of people. Mr. Stoney of Dublin, oneof the best authorities, packed 30 persons upon an area of a littleless than 30 square feet; and at another time he placed 58 personsupon an area of 57 square feet, the resulting load in the two casesbeing very nearly 150 pounds to the square foot. "Such cramming, "says Mr. Stoney, "could scarcely occur in practice, except inportions of a strongly excited crowd; but I have no doubt that itdoes occasionally so occur. " "In my own practice, " he continues, "Iadopt 100 pounds per square foot as the standard working-loaddistributed uniformly over the whole surface of a public bridge, and140 pounds per square foot for certain portions of the structure, such, for example, as the foot-paths of a bridge crossing a navigableriver in a city, which are liable to be severely tried by an excitedcrowd during a boat-race, or some similar occasion. " Tredgold andRankine estimate the weight of a dense crowd at 120 pounds per squarefoot. Mr. Brunel used 100 pounds in his calculations for theHungerford Suspension Bridge. Mr. Drewry, an old but excellentauthority, observes that any body of men marching in step at from 3to 3-1/2 miles an hour will strain a bridge at least as much asdouble the same weight at rest; and he adds, "In prudence, not morethan one-sixth the number of infantry that would fill a bridge shouldbe permitted to march over it in step. " Mr. Roebling says, inspeaking of the Niagara Falls Suspension Bridge, "In my opinion, aheavy train, running at a speed of 20 miles an hour, does less injuryto the structure than is caused by 20 heavy cattle under full trot. Public processions marching to the sound of music, or bodies ofsoldiers keeping regular step, will produce a still more injuriouseffect. " Evidently a difference should be made in determining the load forLondon Bridge and the load for a highway bridge upon a New-Englandcountry road in a thinly settled district. A bridge that is strongenough is just as good and just as safe as one that is ten timesstronger, and even better; for in a large bridge, if we make it toostrong, we make it at the same time too heavy. The weight of thestructure itself has to be sustained, and this part of the load is aperpetual drag on the material. In 1875 the American Society of Civil Engineers, in view of therepeated bridge disasters in this country, appointed a committee toreport upon The Means of Averting Bridge Accidents. We might expect, when a society composed of some hundreds of our best engineersselects an expert committee of half a dozen men, that the bestauthority would be pretty well represented; and such was eminentlythe case. It would be impossible to have combined a greater amount ofacknowledged talent, both theoretical and practical, with a wider andmore valuable experience than this committee possessed. The firstpoint taken up in the report is the determination of the loads forwhich both railroad and highway bridges should be proportioned. Inregard to highway bridges, a majority of the committee reported thatfor such structures the standard loads should not be less than asshown in the following table:-- +-------------------+----------+----------+----------+ | | POUNDS PER SQUARE FOOT. | | SPAN. +----------+----------+----------+ | | CLASS A. | CLASS B. | CLASS C. | +-------------------+----------+----------+----------+ | 60 feet and less | 100 | 100 | 70 | | 60 to 100 feet | 90 | 75 | 60 | | 100 to 200 feet | 75 | 60 | 50 | | 200 to 400 feet | 60 | 50 | 40 | +-------------------+----------+----------+----------+ Class A includes city and suburban bridges, and those over largerivers, where great concentration of weight is possible. Class Bdenotes highway bridges in manufacturing districts havingwell-ballasted roads. Class C refers to ordinary country-roadbridges, where travel is less frequent and lighter. A minority of thecommittee modified the table above by making the loads a littlelarger. The whole committee agreed in making the load per square footless as the span is greater, which is, of course, correct. It wouldseem eminently proper to make a difference between a bridge whichcarries the continuous and heavy traffic of a large city, and onewhich is subjected only to the comparatively light and infrequenttraffic of a country road. At the same time it should not beforgotten, that, in a large part of the United States, a bridge maybe loaded by ten, fifteen, or even twenty pounds per square foot bysnow and ice alone, and that the very bridges which from theirlocation we should be apt to make the lightest, are those which wouldbe most likely to be neglected, and not relieved from a heavyaccumulation of snow. In view of the above, and remembering that amoving load produces a much greater strain upon a bridge than onewhich is at rest, we may be sure, that, as the committee abovereferred to recommend, the loads should not be less than those givenin the table. We can easily see that in special cases they should bemore. There is another point in regard to loading a highway bridge, whichis to be considered. It often happens that a very heavy load iscarried over such bridges upon a single truck, thus throwing a heavyand concentrated load upon each point as it passes. Mr. Stoney statesthat a wagon with a crank-shaft of the British ship "Hercules, "weighing about forty-five tons, was refused a passage overWestminster iron bridge, for fear of damage to the structure, and hadto be carried over Waterloo bridge, which is of stone; and he saysthat in many cases large boilers, heavy forgings, or castings reachas high as twelve tons upon a single wheel. The report of theAmerican Society of Civil Engineers, above referred to, advises thatthe floor system be strong enough to carry the following loads uponfour wheels: Class A, 24 tons; Class B, 16 tons; Class C, 8 tons;though it is stated that these do not include the extraordinary loadssometimes taken over highways. "This provision for local loads, "says Mr. Boller, one of the committee, "may seem extreme; but the jarand jolt of heavy, spring-less loads come directly on all parts ofthe flooring at successive intervals, and admonish us that any errorsshould be on the safe side. " To pass now to railroad bridges, we find here a very heavy loadcoming upon the structure in a sudden, and often very violent, manner. Experiment and observation both indicate that a rapidlymoving load produces an effect equal to double the same load at rest. This effect is seen much more upon short bridges, where the movingload is large in proportion to the weight of the bridge, than uponlong spans, where the weight of the bridge itself is considerable. The actual load upon a short bridge is also more per foot than upona long one, because the locomotive, which is much heavier than anequal length of cars, may cover the whole of a short span, but only apart of a longer one. The largest engines in use upon our railroadsweigh from 75, 000 to 80, 000 pounds on a wheel-base of not over twelvefeet in length, or 2, 800 pounds per foot for the whole length of theengine, and from 20, 000 to 24, 000 pounds on a single pair of wheels. The heaviest coal-trains will weigh nearly a ton to the foot, ordinary freight-trains from 1, 600 to 1, 800 pounds, andpassenger-trains from 1, 000 to 1, 200 pounds per foot. Any bridge isliable to be traversed by two heavy freight-engines followed by aload of three-quarters of a ton to the foot; so that if we proportiona bridge to carry 3, 000 pounds per foot for the total engine length, and one ton per foot for the rest of the bridge, bearing in mindthat any one point may be called upon to sustain 24, 000 pounds, andregarding the increase of strain upon short spans due to high speeds, we have the following loads for different spans exclusive of theweight of the bridge:-- +---------+-----------------+ | SPAN. | LBS. PER FOOT. | +---------+-----------------+ | 12 | 7, 000 | +---------+-----------------+ | 15 | 6, 000 | +---------+-----------------+ | 20 | 4, 800 | +---------+-----------------+ | 25 | 4, 000 | +---------+-----------------+ | 30 | 3, 600 | +---------+-----------------+ | 40 | 3, 200 | +---------+-----------------+ | 50 | 3, 000 | +---------+-----------------+ | 100 | 2, 800 | +---------+-----------------+ | 200 | 2, 600 | +---------+-----------------+ | 300 | 2, 500 | +---------+-----------------+ | 400 | 2, 450 | +---------+-----------------+ | 500 | 2, 400 | +---------+-----------------+ The above does not vary essentially from the English practice, and issubstantially the same as given by the committee of the AmericanSociety of Civil Engineers. The load which any bridge will be required to carry being determined, and the general plan and dimensions fixed, the several strains uponthe different members follow by a simple process of arithmetic, leaving to be determined the actual dimensions of the various parts, a matter which depends upon the power of different kinds of materialto resist different strains. This brings us to the exceedinglyimportant subject of the nature and strength of materials. It has been said that we know what one square inch of iron will hold. Like the question of loads above examined, this is a matter which hasbeen settled, at any rate within very narrow limits, by theexperience of many years of both European and American engineers. Abar of the best wrought-iron an inch square will not break under atensile strain of less than sixty thousand pounds. Only a small partof this, however, is to be used in practice. A bar or beam may beloaded with a greater weight applied as a permanent or dead-load thanwould be safe as a rolling or moving weight. A load may be broughtupon any material in an easy and gradual manner, so as not to damageit; while the same load could not be suddenly and violently appliedwithout injury. The margin for safety should be greater with amaterial liable to contain hidden defects, than with one which is notso; and it should be greater with any member of a bridge which issubjected to several different kinds of strain, than for one whichhas to resist only a single form of strain. Respect, also, should behad to the frequency with which any part is subjected to strain froma moving load, as this will influence its power of endurance. Therule in structures having so important an office to perform asrailroad or highway bridges, should be, in all cases, absolute safetyunder all conditions. The British Board of Trade fixes the greatest strain that shall comeupon the material in a wrought-iron bridge, from the combined weightof the bridge and load, at 5 tons per square inch of the net sectionof the metal. The French practice allows 3-8/10 tons per square inchof the cross section of the metal, which, considering the amounttaken out by rivet-holes, is substantially the same as the Englishallowance. The report of the American Society of Civil Engineers, above referred to, recommends 10, 000 pounds per inch as the maximumfor wrought-iron in tension in railroad bridges. For highway bridgesa unit strain of 15, 000 pounds per square inch is often allowed. Avery common clause in a specification is that the _factor of safety_shall be four, five, or six, as the case may be, meaning by this thatthe actual load shall not exceed one-fourth, one-fifth, or one-sixthpart of the breaking-load. It is a little unfortunate that this term, factor of safety, has found its way into use just as it has; for itby no means indicates what is intended, or what it is supposed to. The true margin for safety is not the difference between theworking-strain and the breaking-strain, but between theworking-strain and that strain which will in any way unfit thematerial for use. Now, any material is unfitted for use when it isso far distorted by overstraining that it cannot recover, or, technically speaking, when its elastic limit has been exceeded. Theelastic limit of the best grades of iron is just about half thebreaking-weight, or from 25, 000 to 30, 000 pounds per inch. A pooriron will often show a very fair breaking-strength, but, at the sametime, will have a very low elastic limit, and be entirely unfit foruse in a bridge. A piece of iron of very inferior quality will oftensustain a greater load before breaking than a piece of the best andtoughest material, for the reason that a tough but ductile iron willstretch before giving way, thus reducing the area of section, while ahard but poor iron will keep nearly its full size until it breaks. Atough and ductile iron should bend double, when cold, withoutshowing any signs of fracture, and should stretch fifteen per cent ofits length before breaking; but much of the iron used in bridges, although it may hold 40, 000 or 50, 000 pounds per inch before failing, will not bend over 90 degrees without cracking, and has an elasticlimit as low as 18, 000 pounds. It is thus full as important tospecify that an iron should have a high elastic limit as that itshould have a high breaking-weight. A specification which allowed nomaterial to be strained by more than 10, 000 pounds per inch, and noiron to be used with a less elastic limit than 25, 000 pounds, would, at the same time, agree with the standard requirement, both inEngland and in the United States, and would also secure a goodquality of iron. Two documents published some time since illustrate the precedingremarks. The first is the account of the tests of the iron taken fromthe Tariffville bridge after its failure, and the second is thespecification for bridges on the Cincinnati Southern Railroad. TheTariffville bridge, though nominally a wooden one, like moststructures of the kind relied entirely upon iron rods to keep thewood-work together. Although the rods were too small, and seriouslydefective in manufacture, the bridge ought not to have fallen fromthat cause. The ultimate strength of the iron was not what it shouldhave been, but yet it was not low enough to explain the disaster; butwhen we look at the _quality_ of the iron, we have the cause of thefall. The rods taken from the bridge show an ultimate tensilestrength of 47, 560 pounds per inch, but an elastic limit of only19, 000 pounds; while the strain which was at any time liable to comeon them was 22, 000 pounds per inch, or 3, 000 pounds more than theelastic limit. The fracture of the tested rods, which, it is stated, broke with a single blow of the hammer very much in the manner ofcast-iron, showed a very inferior quality of metal. The rods broke inthe bridge exactly where we should look for the failure; viz. , in thescrew at the end. No ordinary inspection would have detected thisweakness. No inspection _did_ detect it, but a proper specificationfaithfully carried out would have prevented the disaster. Look now at an extract from the specification for bridges upon theCincinnati Southern Railway:-- "All parts of the bridges and trestleworks must be proportioned tosustain the passage of the following rolling-load at a speed of notless than 30 miles an hour: viz. , two locomotives coupled, eachweighing 36 tons on the drivers in a space of 12 feet, the totalweight of each engine and tender loaded being 66 tons in a space of50 feet, and followed by loaded cars weighing 20 tons each in a spaceof 22 feet. An addition of 25 per cent will be made to the strainsproduced by the rolling-load considered as static in all parts whichare liable to be thrown suddenly under strain by the passage of arapidly moving load. A similar addition of 50 per cent will be madeto the strain on suspension links and riveted connections ofstringers with floor-beams, and floor-beams with trusses. Theiron-work shall be so proportioned that the weight of the structure, together with the above specified rolling-load, shall in no partcause a tensile strain of more than 10, 000 pounds per square inch ofsectional area. Iron used under tensile strain shall be tough, ductile, of uniform quality, and capable of sustaining not less than50, 000 pounds per square inch of sectional area without fracture, and25, 000 pounds per square inch without taking a permanent set. Thereduction of area at the breaking-point shall average 25 per cent, and the elongation 15 per cent. When cold, the iron must bend, without sign of fracture, from 90 to 180 degrees. " A specification like this, properly carried out, would put anabsolute stop to the building of such structures as the TariffvilleBridge, and would prevent a very large part of the catastrophes whichso often shock the community, and shake the public faith in ironbridges. Reference has been made above to the proper loads to beplaced upon wrought-iron when under a tensile strain. Similar loadshave been determined for other materials, and for other kinds ofstrain. The preceding remarks in regard to the loads for which bridges shouldbe designed, and the safe weight to be put upon the material, aregiven to show how far the safety of a bridge is a matter of fact, andhow far a matter of opinion. It will be seen that the limits withinwhich we are at liberty to vary, are quite narrow, so thatbridge-building may correctly be called a science; and there is noexcuse for the person who guesses, either at the load which a bridgeshould be designed to bear, or at the size of the different membersof the structure. Still less can we excuse the man who not onlyguesses, but who, in order to build cheaply, persistently guesses onthe wrong side. It will, of course, be understood, when it is said thatbridge-building may be called a science, that it can only be so whenin the hands of an engineer whose judgment has been matured by wideexperience, and who understands that no mechanical philosophy can beapplied to practice which is not subject to the contingencies ofworkmanship. There are many bridges which will stand the test offigures very well, and which are nevertheless very poor structures. The general plan of a bridge may be good, the computations all right, and yet it may break down under the first train that passes over it. There are many practical considerations that cannot be, at any ratehave not yet been, reduced to figures. It is not enough that thestrains upon each member of a bridge should be correctly estimated, and fall within the safe limits: the different members of the bridgemust be so connected, and the mechanical details such, as to insure, under all conditions, the assumed action of the several parts. Infine, while we can say that a bridge that does not stand the test ofarithmetic is a bad bridge, we cannot always say that a structurewhich does stand such a test is a good one. We often hear it argued that a bridge must be safe, since it has beensubmitted to a heavy load, and did not break down. Such a test meansabsolutely nothing. It does not even show that the bridge will bearthe same load again, much less does it show that it has the propermargin for safety. It simply shows that it did not break down at thattime. Every rotten, worn-out, and defective bridge that ever fell hasbeen submitted to exactly that test. More than this, it hasrepeatedly happened that a heavy train has passed over a bridge inapparent safety, while a much lighter one passing directly afterwardshas gone through. In almost all such cases, the structure has beenweak and defective; and finally some heavy load passes over, andcripples the bridge, so that the next load produces a disaster. Forthe test of a bridge to be in any way satisfactory, we must know justwhat effect such test has had upon the structure. We do not find thisout by simply standing near, and noting that the bridge did notbreak down. We must satisfy ourselves beyond all question that nopart has been overstrained. A short time ago the builders of a wretchedly cheap and unsafehighway bridge, in order to quiet a fear which had arisen that thestructure was not altogether sound, tested a span 122 feet long witha load of 58, 000 pounds; and inasmuch as the bridge did not breakdown under this load, which was less than a quarter part of what itwas warranted to carry safely, the county commissioners consideredthe result eminently satisfactory, and remarked that the test wasmade merely to satisfy the public that the bridge was abundantly safefor all practical uses. The public would, no doubt, have beensatisfied that the Ashtabula bridge was abundantly safe for allpractical uses had it stood on that bridge in the morning and seen aheavy freight-train go over it, and yet that very bridge broke downdirectly afterwards under a passenger-train. Now, according to the common notion, that was a good bridge in themorning, and a very bad bridge, or rather, no bridge at all, in theevening. The question for the public is, When did it cease to be agood bridge, and begin to be a bad one? A test like the one referredto above can do no more than illustrate the ignorance or lack ofhonesty of those who make it, or those who are satisfied with it. Such a test might come within a dozen pounds of breaking the bridgedown, and no one be the wiser. The entire absurdity of such testinghas recently been illustrated in the most decided manner. The verysame company that built the bridge above referred to, made alsoanother one on exactly the same plan, and of almost precisely thesame size, and tested it when done by placing almost exactly the sameload upon it. The bridge did not break down; and the countycommissioners, for whom the work was done, were satisfied that it was"abundantly safe for all practical uses, " accepted it, paid for it;and in less than ten years it broke down under a single team and alittle snow, weighing in all not over one-tenth part of the load thebridge was warranted to carry, and not over one-half the load withwhich it had been previously tested. If this bridge had been "tested"by five minutes of honest arithmetic, it would have been promptlycondemned the very day it was finished. In view of the preceding, what shall we say of a bridge company thatdeliberately builds a bridge in the middle of a large town, where itwill be subjected to heavy teaming, and, owing to its peculiarlocation, to heavy crowds, and warrants to the town that it shallsafely hold a ton per running-foot, when the very simplestcomputation shows beyond chance of dispute that such a load willstrain the iron to 40, 000 pounds per square inch? We are to say, either that such a company is so ignorant that it does not know thedifference between a good bridge and a bad one, or else so wicked asto knowingly subject the public to a wretchedly unsafe bridge. Thecase referred to is not an imaginary one, but existed recently in themain street of a large New-England town. The joints in that bridge, which could safely hold but 20, 000 pounds, were required to hold60, 000 pounds under the load which the builders had warranted thebridge to carry safely. The case was so bad, that, after a lengthycontroversy, the town officers had a thorough expert examination ofthe bridge, which promptly condemned it as in imminent danger offalling, and as having a factor of safety of only 1-15/100, which ispractically no factor at all. Notwithstanding all this, and in theface of the report, the president of the bridge company came out witha letter in the papers, in which he pronounced the bridge "perfectlysafe. " Thus we actually have the president of a bridge company inthis country stating openly that a factor of safety of 1-15/100 makesa bridge perfectly safe, or, in other words, that a bridge can safelybear the load that will break it down, for he very wisely made notthe slightest attempt to disprove any of the conclusions of thecommission; and this company has built hundreds of highway bridgesall over the United States, and is building them to-day wherever itcan find town or county officers ignorant enough to buy them. It might be supposed, that, under the above condemnation, theauthorities controlling the bridge would have taken some steps toprevent the coming disaster. They did, however, nothing of the kind, but allowed the public to travel over it for more than a year, at themost fearful risk, until public indignation became so strong that aspecial town-meeting was called, and a committee appointed to removethe old bridge, and to build a new one. One of the worst cases of utterly dishonest bridge-building that wehave had of late years in Massachusetts, was that of the iron highwaybridge across the Merrimac River at Groveland, a few miles belowHaverhill, one span of which broke down in January, 1881. This bridgewas built in 1871-1872, and consisted of 6 spans, each about 125 feetlong. The whole cost of the structure was $80, 000, and the contractprice for the iron-work was $28, 000. The company which made thatbridge, agreed in their contract to give the county a structure thatshould carry safely 3, 000 pounds per running-foot besides its ownweight; but they built a bridge, which, if they knew enough tocompute its strength at all, they knew perfectly well could notsafely carry over one-quarter part of that load. In fact, the weightof the bridge alone is more than it ever ought to have borne. Thecompany warranted each span of that bridge to carry safely a net ormoving load of 165 tons, and it broke down under a single team and asmall amount of snow. The company warranted that bridge to carrysafely a load which would strain the iron to 50, 000 pounds per inch, when it knew perfectly well that 15, 000 pounds per inch was the mostthat could safely be borne. There are several concerns in the United States which make aspecialty of highway bridges, and which, taking advantage of theignorance of public officials, are flooding the country with bridgesno better than that at Groveland. On an average, at least twenty ofthese miserable traps tumble down every year, and nothing is done tobring the guilty parties to punishment. Dishonest builders cheatignorant officials, and the public suffers the damage and pays thebills. Is human life worth enough to pay for having these structuresinspected, and, if found unsafe, strengthened or removed? Can we doany thing to prevent towns and counties from being imposed upon bydishonest builders? We certainly can, if those who control thesematters care enough about it to do it. There are two ways of buying abridge, --a good way and a bad one; and these two ways are so plainthat no one can misunderstand. To buy a bad bridge, just as soon asyour town or county votes money for a new bridge, certain agents--andthey are as numerous as the agents for sewing-machines orlightning-rods--will call on, or write to, the town or countyofficers, and will offer to build any thing under heavens you want ofany size, shape, or material, and for almost any price. They willproduce testimonials from all the town and county officers in thecountry for the excellence of their bridges, and would not hesitateto give reference, even, for their moral character, if you should askit. If they find that you don't know any thing about bridges, theywill, to save you the trouble, furnish a printed specification; whichdocument will commit you to pay the money, but will not commit thebridge company to any thing at all. When the bridge is put up, younever will know whether the iron is good or bad, nor whether thedimensions and proportions are such as to be safe or not. You willknow that you have paid your money away, but you never will know whatyou have got for it until some day when your bridge gets a crowd uponit, and breaks down, and you have the damage to pay. This mode ofbuying a bridge is very common. To buy a good bridge, first determineprecisely what you want; and if you don't know any thing in regard tobridge-building yourself, employ an engineer who does, to make aspecification stating exactly what you want, and what you mean tohave. Then advertise for bridge-builders to send in plans andproposals. Let the contractors understand that all plans andcomputations are to be submitted to your engineer, that all materialsand workmanship will be submitted to your inspectors, and that thewhole structure is to be made subject to the supervision of acompetent engineer, and accepted by him for you. You will find atonce, that, under such conditions, all travelling agents and buildersof cheap bridges will avoid you as a thief does the light of day. Youwill have genuine proposals from responsible companies, and theirbids should be submitted to your engineer. When you have made yourchoice, let the contract be written by your lawyer, and have theplans and specifications attached. Employ a competent engineer toinspect the work as it goes on; and when it is done, you will have abridge which will be warranted absolutely sound by the bestauthority. This mode of buying a bridge is very uncommon. The Ashtabula bridge, it is stated in the report of the committee ofthe Ohio Legislature appointed to investigate that disaster, hadfactors, --we can hardly call them factors of safety, --in some partsas low as 1-6/10 and 1-2/10, such factors referring to thebreaking-weight; and even these factors were obtained by assuming theload as at rest, and making no allowance for the jar and shock from arailroad train in motion. Well may the commissioners say, as they doat the end of their report, "The bridge was liable to go down at anytime during the last ten years under the loads that might at any timebe brought upon it in the ordinary course of the company's business, and it is most remarkable that it did not sooner occur. " One point always brought forward when an iron bridge breaks down, isthe supposed deterioration of iron under repeated straining; and weare gravely told that after a while all iron loses its fibre, andbecomes crystalline. This is one of the "mysteries" which somepersons conjure up at tolerably regular intervals to cover theirignorance. It is perfectly well known by engineers the world over, that with good iron properly used, nothing of the kind ever takesplace. This matter used to be a favorite bone of contention amongengineers, but it has long since been laid upon the shelf. Noengineer at the present day ever thinks of it. We have only to allowthe proper margin for safety, as our first-class builders all do, andthis antiquated objection at once vanishes. The examples of the longduration of iron in large bridges are numerous and conclusive. TheNiagara-Falls railroad suspension bridge was carefully inspectedafter twenty-five years of continued use under frequent and heavytrains, and not only was it impossible to detect by the severesttests any defect in the wire of the cables, but a piece of it, beingthrown upon the floor, curled up, showing the old "kink" which theiron had when it was first made, and wound on the reel. The Menaisuspension bridge, in which 1, 000 tons of iron have hung suspendedacross an opening of 600 feet for sixty years, shows no depreciationthat the most rigid inspection could detect. Iron rods, recentlytaken from an old bridge in this country, have been carefully testedafter sixty years of use, and found to have lost nothing, either ofthe original breaking-strength, or of the original elasticity. The question is frequently asked, Does not extreme cold weaken ironbridges? To this, it may be replied, that no iron bridge, made by areliable company, has ever shown the slightest indication of anything of the kind, though they have been used for many years inRussia, Norway, Sweden, and Canada, and nothing that we know inregard to iron gives us any reason to suppose that any thing of thekind ever will happen. But here, again, every thing turns upon thequality of the iron. Iron containing phosphorus is "cold-short, " orbrittle when cold, and will break quicker under repeated and suddenshocks in cold weather than when it is warm. With good iron, properlyused, we need have no fear on this point. The securing such iron is amatter to which the utmost attention is paid by our first-classbridge-building firms, but it is a matter to which no attention ispaid by the builders of cheap bridges. We might suppose that aperson, in putting an insufficient amount of iron into a bridge, would be careful to get the best quality; but exactly the reverseseems to be the case, on the ground, perhaps, that the less of a badthing we have, the better. Many persons, in building wooden bridges, take no pains to get ironrods which are suitable for such work, but purchase what is easiestto be had in the market, and in many cases never find that the ironwas bad until a bridge tumbles down. There are, without the slightestquestion, hundreds of bridges now in use in this country, which, asfar as mere proportions and dimensions go, would appear to beentirely safe, but which, on account of the quality of the iron withwhich they are made, are entirely unsafe; and there always will be, as long as public officials purchase iron which they know nothingabout, to put into bridges. When a bridge is finished, the ordinaryexaminations never detect the quality of the iron; so that the wiseremarks of many inspectors, or the opinions of those in charge ofthese structures, as to the exact condition of a bridge, are oflittle or no value. We often hear iron bridges condemned, while wooden ones, so called, are supposed to be free from defects. It does not seem to occur topersons holding such ideas, that wooden bridges rely just as muchupon the strength of the iron rods that tie the timbers together, asupon the timber. As a matter of fact, where one iron bridge falls, adozen wooden ones do the same thing. One very decided advantage whichan iron bridge has over a wooden one, is that we can make sure ofgood iron in the beginning, and that we can also be sure that it doesnot decay; while, however good our timber may be in the beginning, wenever can be entirely sure of its condition afterwards. There arewooden bridges now standing in this country, all the way from sixtyto eighty years old, which are apparently as good as ever; whilethere are others, not ten years old, which are so rotten as to beunfit for use. It will not do to assume, that, because no defects arevery evident in a wooden bridge, therefore it has none. When a woodenbridge, originally made of only fair material, has been in use underrailroad trains for twenty-five or thirty years, and in a positionwhere timber would naturally decay, we are bound to suspect thatbridge. To assume such a bridge to be all right until we can prove itto be all wrong, is not safe. To assume a bridge to be all wronguntil we can prove it to be all right, is a safe method, though not apopular one. Any person who has had occasion to remove old woodenbridges, will recall how often they look very much worse than wasanticipated. There is one defect in railway bridges which has often led to themost fearful disasters, and which, without the slightest question, can be almost entirely, if not entirely, removed, and at a moderatecost. At least half the most disastrous failures of railroad bridgesin the United States have been due to a defective system offlooring. With a very large proportion of our bridges, the failureof a rail, the breaking of an axle, or any thing which shall throwthe train from the track, is almost sure to be followed by thebreaking down of the bridge. The cross-ties are in many cases veryshort, and the floor is proportioned for a train _on_ and not _off_the rails. When an engine on such a floor leaves the track, itplunges off the ends of the cross-ties into the open space betweenthe stringers and the chords, and generally wrecks the bridge. Toprevent this, the cross-ties should be long and well supported, andplaced so close that a derailed engine cannot cut through them. Thetrack should also be provided with guard-timbers well fastened, andthe width between the trusses should be so great that the wheels of aderailed train will be stopped by the guard-rail before the side ofthe widest car can strike the truss. The importance of a substantial floor system has been very fullyrecognized by the railroad commissioners of Massachusetts, who haverecently issued a very suggestive circular, accompanied by numerousexamples of track construction for railway bridges. If this circularreceives proper attention, it is sure to produce good results. Another point which has often been neglected, is making sufficientprovision to resist the force of the wind. A tornado, such as is notuncommon in this country, will exert a force of 40 pounds per squarefoot, which upon the side of a wooden bridge, say of 200 feet span, and 25 feet high, and boarded up as many bridges are, would amount toa lateral thrust of no less than 100 tons; and this load would beapplied in the worst possible manner, i. E. , in a series of shocks. There have been many cases in this country where bridges have beenblown down; and a case recently occurred where an iron railroadbridge of 180 feet span, and 30 feet high, and presenting apparentlyalmost no surface to the wind, was blown so much out of line that thetrack had to be shifted. The recent terrible disaster at the Firth ofTay was, no doubt, due to this cause. At the time of the Tariffville catastrophe, it was gravely stated atthe coroner's inquest, and by railroad officers who claimed to knowabout such things, that the disaster was caused by the tremendousweight of two locomotives which were coupled together, and it wasstated that one engine would have passed in safety; and directlyafterwards the superintendent of a prominent railroad in New Englandissued an order forbidding two engines connected to pass over anyiron bridges. It is all very well for a company to issue such anorder, so far as it may give the public to understand that it isdetermined to use every precaution against disaster; but such anorder may have the effect of creating a distrust which really oughtnot to exist. If a railway bridge is not entirely safe for twoengines, it is certainly entirely unsafe for one engine and the trainfollowing; the only saving in weight by taking off one engine beingthe difference between the weight of that engine and the weight ofthe cars that would occupy the same room. For example, a bridge of200 feet span will weigh 1, 500 pounds per lineal foot. An engine andits tender will weigh 60 tons in a length of 50 feet, and a loadedfreight-train may easily weigh 2/3 of a ton per lineal foot. Thetotal weight of the span, with two engines, and the rest of thebridge covered with loaded freight-cars, would thus be 320 tons. Ifwe take off one engine, and fill its place with cars, we take off 60tons, and put in its place 33 tons; i. E. , we remove 27 tons, or justabout 1/12 of the working-load. Taking off a large part of theworking-load, however, is taking off a very small part of thebreaking-load; with a factor of safety of six, for example, takingoff 1/12 of the working-load is taking off less than 1/70 of thebreaking-load. An order, therefore, like that above, can only be ofuse when the working-load and the breaking-load are so nearly alikethat the actual load is a dangerous one: that is when the bridge isunfit for any traffic whatever; so that, if such an order was reallyneeded, it would, in itself, be, in the eyes of an engineer, acondemnation of the bridge. Having seen something of the structures which require inspecting, letus now see what kind of inspection we have in this country, and theresult of it; and let us also see the inspection which we might have, and the results that might be produced. Looking first at railroadbridges, it might be supposed that no one could be so much interestedin keeping such structures in good order as the companies which ownthose bridges, and which have the bills to pay in case of disaster. This is, of course, so; but, in spite of the fact, the Ashtabulabridge broke down, on one of the best managed lines in the country, and cost the company over half a million dollars in damages. Norailroad bridge ever broke down, which the owners were not interestedin keeping safe; but there is always a desire to put off incurringlarge expenses until the last moment, and thus weak bridges are veryoften let go too long. A short time since, the superintendent of alarge railroad stated plainly before a legislative committee, thatmany of the smaller roads were not safe to run over, but that suchroads were having a hard time, and could not afford to keep theirtrack and bridges in a safe condition. During the past ten years overtwo hundred railroad bridges in the United States have broken down. These bridges were all kept under such inspection as the railroadcompanies owning them considered sufficient, or such as they couldafford; but either the supervision was defective, or the companiesknowingly continued the use of unsafe bridges, and this fault has byno means been confined to the smaller and poorer roads. It wouldseem, therefore, that inspection by the companies themselves has notbeen sufficient. It certainly has not been enough to prevent twohundred disasters in ten years. It is the custom in several of theUnited States to maintain what is termed a railroad commission. Theoriginal intention seems to have been for these commissions to keepthe railroads under some kind of inspection, and in some way toassist in settling any questions that might arise between differentcompanies, and between railroad companies and the public. As far aswe can judge by the results produced, in the States where thesecommissions have been established, we can hardly pronounce them ofany very great importance. In many States, it is very certain, that, in regard to matters of inspection, the work of these boards has beensimply a farce; and it could hardly be otherwise in a State whichpays its commissioners only $1, 000 salary, or, worse yet, as in somecases, only $500. Add to this, that in many cases the appointmentshave been purely political ones, and we can see the absurdity ofexpecting any results of value. We should hardly suppose that threemen, in many cases entirely unacquainted with mechanical matters, could by riding over a railroad once or twice a year, occasionallygetting out to examine the paint on the outside of the boards, whichconceal a truss from view, judge very correctly of the elastic limitof the iron rods which they have never seen, and of which they donot even know the existence. For ample proof of the utter inefficiency of the present system, wehave only to compare the reports of the railroad commissioners inalmost any State, with the actual condition of the structuresdescribed. In one State a late annual report covers a whole railroadwith the remark, "All of the bridges on this line are in excellentorder;" and yet there were at that very time, and are now, on thatroad, several large wooden bridges with a factor of safety referredto the breaking-weight of not over _two_ under a fair load, assumingthe iron rods to be of the very best material, --a point upon whichthere is no evidence whatever. There is, in fact, no difference which any ordinary inspection woulddetect between these bridges as they stand to-day, and theTariffville bridge as it stood the day before it fell. In anotherState, an iron bridge is in use under heavy trains, which has afactor of only 2-1/2 instead of 6, and yet the State reportpronounces it an excellent structure and a credit to the railroadcompany, which recklessly allows its trains to pass over it. In yetanother State, the commissioners in 1874 reported that a certainbridge should be removed; and this was quite correct, as it was aneminently unsafe bridge. In 1875 they suggested the same thing again. In 1876 they say, "This bridge must be rebuilt the coming spring. " In1877 they again reported, "This bridge must be rebuilt before thespring opens. It is old, and will not be safe for the passage oftrains over it, if the ice or freshet should take away the temporarytrestles, which now in a great measure support the truss. " A year later than that, in 1878, a public protest was made againstthe further use of that bridge, as the lower chords were rotten, broken, pulled apart, and the only thing that held it up was atrestle, liable at any time to be knocked out by the ice; and yet, after all this, in reply to the protest, the commissioners repliedthat they had just "tested" the bridge by running an engine over it, and pronounced it "safe for the present, " whatever that may mean. Now, just how it was that this bridge, which was old, rotten, andworn out, which the commissioners themselves had condemned for foursuccessive years, which they had said two years before must berebuilt the coming spring, and which relied entirely upon a trestleliable at any time to be carried away, had suddenly become "safe forthe present, " is not plain to see. Evidently such inspection as this is of no value. It is exactly thisutterly incompetent and dishonest inspection, this guessing that abridge will stand until it falls, that lies at the bottom of half thedisasters in the country. It is under exactly such inspection thatthose wretched traps, the Ashtabula and Tariffville bridges, fell, and killed over one hundred people. No wonder that railroad officialshave an undisguised contempt for State inspection. While in a fewStates the inspection is not quite so bad as that referred to, as ageneral thing it is no better; and we have no right to expect anything better under the present system. The State inspection which wehave had throughout this country has not prevented the breaking downof one hundred bridges in the past ten years. Twenty-five States haverailroad commissions; but in nine of them the commission consists ofonly a single man, who, in some cases, is paid only $500 a year. AState can pay $500 a year for having its bridges inspected, and itwill get such service as never did and never will prevent a disaster;or it can pay a good price for competent inspection, which will beworth ten times the money to the State. The money which the LakeShore Railroad paid in damages for the Ashtabula disaster alone, would have employed permanently six men at $5, 000 a year each, and ahundred lives would have been saved besides. With regard to highway bridges, we are, if possible, even worse offthan in regard to railway bridges; for in the case of suchstructures, neither the owners nor the State make any pretence atinspection. It is impossible to say how many highway bridges havebroken down during the past ten years, but it is estimated bybridge-builders that the number cannot be less than two hundred. Thisis, no doubt, far within the truth; and by far the larger part ofthese structures are not old wooden bridges, but are new bridges ofiron. If we knew positively that in just six months a terrible disasterwould occur under the present system of bridge inspection, and knewalso, that, by a better system, such disaster would certainly beprevented, it is possible that a change might be made. We know thata proper method of building and inspecting bridges would certainlyhave prevented the disasters at Ashtabula, Tariffville, and Dixon. Weknow that the inspection which those bridges received, did notprevent three of the most fearful disasters the country has everseen. Admitting, now, that structures so important to the publicsafety as bridges, both upon roads and railroads, ought to be keptunder rigid inspection and control, and that no system at presentexisting has been able to prevent the most fearful catastrophes, whatshall we do? Directly after the Ashtabula disaster, the Ohiolegislative committee, appointed to investigate that affair, presented to the Legislature a bill, "To secure greater safety forpublic travel over bridges, " in which was plainly specified the loadsfor which all bridges should be proportioned, the maximum strains towhich the iron should be subjected, and a method for inspecting theplans of all bridges before building, and the bridges themselvesduring and after construction. The governor, with the consent of theSenate, was to appoint the inspector for a term of five years at asalary not exceeding $3, 000 a year, such inspector to pass asatisfactory examination before a committee of the American Societyof Civil Engineers, themselves practical experts in bridgeconstruction, and he was also to take a suitable oath for thefaithful performance of his duty. This bill never became a law. Anappropriation was made for a short time to pay for certainexaminations, and there the matter stopped. The committee of the American Society of Engineers were not agreedupon this matter. Messrs. James B. Eads and Charles Shaler Smithsuggested the appointment in each State of an expert, to whom allplans should be submitted, and by whom all work should beinspected, --such expert to have been examined and approved by theAmerican Society of Civil Engineers. The inspector was also to visitthe scene of every accident, so called, and to ascertain, as far aspossible, the cause. Messrs. T. C. Clarke and Julius W. Adamsbelieved, that, in the present state of public opinion, the abovemethod would be impracticable, and feared, that, if inspectors wereappointed, it would be by political influence, and that the resultwould be worse than at present, as the inspectors would beinefficient, and yet, to a great extent, would relieve the owners ofbad bridges from legal responsibility. They held that the best thatcould be done would be to provide means, in case of disaster, to fixplainly the responsibility, and recommended, First, that the standardfor strength fixed by the Society should be the legal standard; and, in case it should be found that any bridge was of less strength thanthis, it should be taken as _prima facie_ evidence of neglect on thepart of the owners. Second, that no bridge should be opened to thepublic until a plan giving all dimensions, strains, and loads, swornto by the designers and makers, and attested by the corporationhaving control of it, had been deposited with the American Society;and further, that the principal pieces of iron in the bridge shouldbe stamped with the name of the maker, place of manufacture, anddate. Messrs. A. P. Boller and Charles Macdonald looked rather towardeffecting the desired result by so directing public sentiment bykeeping the correct standard for bridges before it, that it wouldeventually compel the passage of the necessary laws. Whether it is possible, in this country, to make an appointmentdependent purely upon honesty and capacity, and free from politicalinfluence, may well be doubted. No competent engineer would bewilling to accept a position which would place upon him so great aresponsibility, except under a very carefully devised plan. A veryconsiderable force of inspectors would be required to carry out asystem which should produce the desired result. The amount of workto be done at the commencement would be very great, as no properinspection has ever been made of the greater part of the bridges inthe country, of which the number is very large. If any such plan asabove suggested should be found feasible, the inspectors should havein their possession a complete set of plans of every bridge ofimportance in the State, with all the computations of its strength, and as complete a history of each structure from its commencement ascan be made up, all this to be supplemented by periodic examinations. If, from such records, we find that a bridge was made of ordinarygreen timber twenty-five years ago, and that it has been gettingrotten ever since; that it has rods of common merchant iron that werebought by some person, not specially acquainted with the business, from an unknown firm, --we had better pull it down before it falls. If, from such records, we find an iron bridge built twenty-five yearsago by an unknown company, with iron, at best, of a doubtful quality, and having a factor of three or four for the rolling-stock and speedsof twenty years ago, instead of a factor of six for the rolling-stockand speeds of to-day, we had better remove that bridge before itremoves itself. Such a record would be the property of the State, always accessibleto any one, and would be handed down, so that the knowledge of oneperson would not expire with his term of office. No bridge should beerected in any State without first submitting the plans to theinspector, and receiving his approval, and depositing with him acomplete set of the plans and computations for the work. By thisapproval is not meant that the inspector is merely to give afavorable opinion as to the plan, but that he is to find, as a matterof fact, whether the proposed dimensions and proportions are such aswill make a safe bridge--and just what a safe bridge is, can beplainly defined by law, as it is in Europe, and as it has beenproposed by the American Society of Civil Engineers. For example, ifthe law says that an iron railway bridge of 100 feet span shall beproportioned to carry a load of 3, 000 pounds per lineal foot besidesits own weight, and that, with such a load, no part shall be strainedby more than 10, 000 pounds per inch, all the inspector has to do isto go over the figures, and see that the dimensions given on the planare such as will enable the bridge to carry the load withoutexceeding the specified strains. When the work is erected, theinspection must show that the plan has been exactly carried out, thatthe details are good, and proper evidence of the quality of thematerial used should also be given. Such inspection as this would atonce prevent the erection of bridges like those at Ashtabula andTariffville, and would save the public from such traps as those thatfell at Dixon and at Groveland. Perhaps the most difficult thing todo will be to get satisfactory evidence in regard to the bridges thathave been for a considerable time in use, and of which we do not knowthe history. This will be especially true in regard to the woodenbridges, of which there are so many about the country. Not only is itvery difficult to be sure of the exact condition of the timber, butit is equally hard to tell any thing about the iron. The Tariffvillebridge fell on account of defective iron, and the defect was of sucha nature as to defy any ordinary inspection. What do we know to-dayof the quality of the iron rods in any wooden bridge inMassachusetts? It is very doubtful if the best inspection we have inthe United States at the present time would have found any defect soevident in the Tariffville bridge as to condemn it as unfit for thepassage of trains. There are hundreds of exactly such bridges allover New England, as far as we can tell by the best inspection we nowhave, made on the same plan, with no more material, and of which weknow just as little of the quality of the iron as we did in theTariffville bridge. Of course we cannot expect to get a perfect system all at once. Anyplan which might be proposed would, no doubt, be found more or lessdefective at first. We can hardly get a system worse than the one wenow have, which allows forty bridges to break down every year. We mayget a better one. To make the public see the need of such a system isthe first step to be taken. * * * * * LEE AND SHEPARD'S POPULAR HANDBOOKS. 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