Hazards of the "Sand Hog"

An article showing that there is romance even in the building of bridges and that no bridgebuilding task is too big for Canadians to tackle.

C. R. YOUNG September 15 1923

Hazards of the "Sand Hog"

An article showing that there is romance even in the building of bridges and that no bridgebuilding task is too big for Canadians to tackle.

C. R. YOUNG September 15 1923

Hazards of the "Sand Hog"

An article showing that there is romance even in the building of bridges and that no bridgebuilding task is too big for Canadians to tackle.

C. R. YOUNG

sociate Professor Structural Kngineering, University of Toronto

BRIDGE BUILDING in Canada has for many years been characterized by achievements not surpassed in any other country. The greatest tubular bridge of all time was built in this country more than sixty years ago; the most massive steel viaduct ever constructed accomodates the trains of a Canadian railway; and the widest

single opening ever spanned by the daring of a bridge engineer is across a Canadian

stream. Further, there were thrown across the Niagara River, as joint undertakings of our southerly neighbors

.4r.tt •~~ar th~ n~t sus~ u~t'!1 k~uI~ •*_~ `~t~~• r~t !~t. - w,it~ was f~r t~.'nt~ t rth r do t • pr~-~~ Ttt It 0 1 I.'~~!III 1 t of bridge ad~ 1. - `udil.. f `w~It~ otb.-'r - .:htp. i' ri it

¶ hi c.i~n Irtiiv ul n.e. ti!Ii.~L! xit i-' . btg hi `~`It~ rciL:~ tu It.

Crossing St. Lawrence in Tubes

• I inar~y unp~r j

ui *`ourage, tre built in what ic ut 1 t h pin . r days in the development of I'l lfl .trLdd.i. it was nt until the cont~., if t `. a i~' na • II ular iariig,' across the St. - iTs' ¶ t ri.1 a pp~ }ì~ years I 54 and v at thi~ .ahaI the taga of distinction ti `~buit'ii -t t It t~ true that R} ert Stephenson. f th~ \ .~!oria tr~I~ta, had in his Britannia t~ay ruinlir in \VaIe-, already exceeded .~i Spat tantiriseti ii the Canadian - t~" i~• . hu t ti. ft r ri!~ could at the time compare ts vt ..ni1 a. a. I `It g-aat work which in 1 s61) .; I -ii,.~!ly nIl' i fr tatlj ty a Prince of \Vales a pilar i pr-ant bearer of that title. h• iS~ had speit many stt-at,I.-~ and anxious t ! fIr t a ta I tilewere being hOi~tP(l p tin ar titr ifty fier~. but in this hitherto tr.Ia a-~tl r; ir;a~ed himself. T the proud f -i-a' I 1 liiint.jha rs a new lustre was dais I litre a t~~A tire a mile i~'ti a quarter long, Is s-uty-ti'.e tubular -ran~. in One case an great 0) f . tult .t trt,wei.t river, which in • r i~.arna~ a . ip'~tI i.. griffing, well-nigh irreace i-hi. •l ii -p-rt~ a taoI-trorn of grinding ffe a 1 t rx.i~r . ia~. ..ir'~. no human construc in ri ru 1 `i -a ai .i h a it! a-itt atton of natural et th~ a. r. per.A1Iraed and con by .pIe,.a'a at1 his a--(latC~ are still in u~ ara'l at~. an' itch :eater load than most people tti)ugr id -.--r i.e ii~-t'I iJ~(t them.

Victoria Bridge Renewed

FHE late nineties, the astounding increase in

iffic and in the weight of locomotives and trains, i with the corrosive onslaught of gases from iming engines, made it necessary to replace the aular superstructure with a double-track one of greater capacity. So safely had the original

i used mge,

convincing examples of the ability of the engineer to construct mason r. which is seemingly as enduring as the eternal hills.

The new superstructure, consisting of simple truss spans, of the same length as the old tubes, was erected around and enclosing the latter—a procedure rendered possible by reason of the fact that the new spans had

greater cross-sectional dimensions than the old. Once

loads could be transferred to the new superstructure,

the old tubes were cut up and removed in sections—

the whole without accident and with a total delay to traffic of only twenty-five hours in five months. The growth in train weights occurring in forty years may be appreciated from the fact that the engi-

neers of the bridge of 1860 experienced great difficulty in making up a special test loading to weigh one ton per foot of track, whereas the new bridge was designed for a regular working load equivalent to about two and one-half tons per foot of each track, or equal

to five times the total capacity of the old structure.

Bridges at Lachinej

\yf EANTIME, the eastward extension of the Canadian Pacific Railway out of Montreal made it necessary to seek a crossing of the St. Lawrence for that road. This was fixed at Lachine, some two miles above the rapids. While the total bridging here required was a third less than for the Victoria bridge crossing, the structure erected during the years 1885-1887 was in certain respects bolder. The strong current, running eight or ten miles an hour and a depth of water ranging from twenty to ninety feet made the placing of falsework in the channel of the river so hazardous that the projection of the two 408-foot channel spans outward from their piers by the cantilever method was necessary.

In the building, and later rebuilding, of this bridge which has its southern approach near the Indian village of Caughnawaga, the sometime scalphunting red men had a share. Numbers of them have for many years been employed at the bridge works across the river at Lachine and have found the snap and dolly useful substitutes for the tomahawk. Of those who lost their lives in the great Quebec bridge disaster several were Indians.

Full service was given by the old structure until 1910, when, like its old-time neighbor opposite Montreal, it had to give way to a double-track bridge capable of accommodating the ever-increasing rolling loads. Here, again, the original masonry was found to be unimpaired, requiring merely certain necessary extensions to accommodate a second track and to shorten certain spans by half. How difficult pier building in the St. Lawrence is at this point may be gauged from the fact that the pressure of the current against the caisson for a pier in the deeper portion of the river amounted to upwards of 100 tons. Eddies, cross-currents and whirlpools, combined with the fact that enormous boulders cover the bottom, made sub-aqueous and floating operations extremely hazardous to both life and property, and necessitated the greatest care in the conduct of re-construction operations. Needless to say the engineers in charge watched with unbroken vigilance, and not a little anxiety, the critical stages of this most important part of their work.

In re - building

the superstructure it was essential that there be no interference with regular traffic. To ensure this, it was decided to build two independent single-track structures on the widened piers. When one of these bridges had been erected alongside the old single - track bridge, traffic was diverted to the former and the latter replaced at leisure by a new bridge. Here was a piece of intrepid and large - scale juggling which might have proved disastrous if anything had been let fall. The two

great channel spans of each bridge were rolled out over the openings by allowing their rear ends to trail on the adjacent completed spans and their forward ends to rest on moving scows. Each of these 408-foot spans had a launching weight of 1,300 tons. The delicacy with which the launching process was carried out by the Canadian company erecting the bridge is apparent when it is learned that in a typical case the last three inches of travel required was exactly covered by the operator of the hauling engine on receipt of a signal

given by an observer 800 feet away.

Farther up the St. Lawrence.great bridges had been thrown across at two points. The first was built at Coteau in 1890 for the Canada Atlantic Railway and involved in all 4,025 feet of bridging. The ten spans of the channel section were, in spite of the swift current . floated into position on scows and safely placed on their piers. The aecond, built at Cornwall, for the New York and Ottawa Railway, in the late nineties was unfortunately attended by the collapse of two spans through the giving way

of the trelcherous foundation of a pier. What was thought to be a substantial bed of hardpan proved to be but a two-foot stratum overlying fifteen feet of soft clay. When the weight of one of the channel piers was augmented by the growing weight of the steel superstructure, still in process of erection, the pier suddenly sank out of sight

and precipitated the spans in the river, killing fifteen men and injuring sixteen others.

The Cornwall disaster disturbed the ultimate confidence of neither the engineer nor of those who had brought their brawn into play far above the treacherous St. Lawrence. They promptly cleared away the debris and completed the bridge. Men who follow great bridge building ventures are not dismayed by the ever-present hazards of their work. There is in it something of the lure of battle. The fascination of inserting erection bolts in a great member as it swings into place a hundred or more feet above a torrent—with the odd chance of tumbling in—is irresistible with the red-blooded men who build bridges. They follow the game wherever it is played, and if occasionally some one is killed, it becomes the more alluring. It is a man’s job.

Bunching Bridges at St. John

THERE is but one practicable crossing of the St.

John river in the neighborhood of the city of St. John. N.B. At the narrow gorge where may be seen that singular natural phenomenon, the Reversing Falls, there is a zone of some 200 feet, which has accommodated several of the most notable bridges of Canada. Here in 1852-53 Captain (later General) Edward W. Serrell —a pioneer in bridge building—constructed a highway suspension, bridge with a span of 628 feet which was long a familiar landmark at St. John, and continued to serve the country thereabouts down to 1914. In that year it was removed to give place to a modern structure of far greater capacity. On demolition, the sixty-year old wire cables were found to be as good as when new. In this circumstance is found an indication of the permanence attainable in the works of a skilled engineer.

One of the flattest arches on record, but an unusually graceful structure, succeeded the old suspension bridge. Its span of 565 feet exceeds that of any other arch span situated wholly in Canada. Since the great depth of the channel, the strong current and the necessity for maintaining a clear waterway precluded the erection of falsework in the river, the two halves of the arch were cantilevered out from the rocky banks until they met truly at the centre, precisely as pre-calculated. One is disposed to ask what would have happened if they had not. That would have been serious for both the engineers and the owners. The rarity of errors of this kind is an illuminating comment on the skill with which the engineer does his work.

Nearby, there has been erected, in 1884, a railway cantilever bridge which was supplemented in 1921 by an original type of cantilever built by the C.P.R. Sometimes engineers are taken to task for not foreseeing all possible contingencies and providing for them in their estimates. This bridge, however, costing $900,000, was completed within one per cent, of the estimate.

Notable Construction at Niagara

STIRRING historic events have had setting along the Niagara frontier, and during the past threequarters of a century it has witnessed some of the world’s great engineering achievements. The narrowness of the gorge below the falls has been a perpetual challenge to the bridge builder.

In 1844, William Hamilton Merritt, of St. Catharines, learning of the success of the suspension

bridge at Freiburg, Switzerland, proposed a similar structure for Niagara. Four prominent bridge engineers, Charles Ellett, John A. Roebling, Samuel Keefer and Edward Serrell reported favorably upon the project. Each of these men in later years actually built a bridge across the gorge. In 1847, Ellett was given a contract to erect a suspension span of 800 feet for combined roadway and railway traffic, but lack of funds prevented him from carrying out more than a narrow roadway structure. This bridge was erected in 1848 on the site of the present Grand Trunk Railway arch. To carry the first string across, a kite was used; this served to draw a larger cord over, which in turn, pulled the rope attached to the end of the first wire cable. So proud was Ellett of his achievement, that before the side railings were placed, he rode his horse triumphantly across the 7 ''¿-foot platform at a height of 225 feel above the river. Ellett’s bridge continued in use until replaced by the celebrated railway structure of the same type in 1855.

Doing the Impossible

TN MANY respects the most remarkable bridge ever A built across the Niagara gorge was Roebling’s railway suspension bridge, completed in 1855. Robert Stephenson, the most distinguished bridge engineer in Europe at that time, seriously doubted the possibility of ever constructing a suspension bridge to carry railway traffic successfully, because of the alarming deflection of the floor under heavy moving locomotives and cars.

Consequently, he had directed his genius to the development of the tubular girder for long span railway bridges, with a success to which the great Britannia, Conway and Victoria bridges already, or later, bore witness.

John A. Roebling, however, was confident that he could build a suspension bridge which would be rigid enough to accommodate the heaviest railway trains of the time, and at the G.T.R. crossing which, thanks to his genius, is known to this day as “Suspension Bridge,” he demonstrated the soundness of his views. Excessive deflection of the floor, often taking the form of a wave a foot or more high preceding the locomotive, had caused the abandonment for railway traffic of several European suspension bridges. Roebling overcame this by devices of his own and achieved what had been declared impossible.

After many repairs, renewals and reinforcements to meet the ever-growing traffic, the old suspension structure, with a record of forty-three years of arduous service to its credit, was replaced by the present G.T.R. railway arch in 1897. When the original Roebling bridge was built, locomotives did not exceed twenty-five tons in weight and cars had a capacity of at most sixteen tons; but by 1897, locomotive weights had risen to 100 tons, and cars often carried thirty tons of material.

Arch Projected Over Torrent

EXTREME care in planning the replacement was necessary in order that the heavy traffic crossing the river at the point be not delayed. Placing of falsework in the Niagara River at the jump-off of the Whirlpool Rapids, where the water was of unknown

depth and ran at sixteen miles an hour, was, of course, out of the question; neither could the old suspension bridge carry any of the weight of the new structure, and at the same time look after its regular duty of supporting train and vehicular loads. To meet these difficulties, L. L. Buck, able successor of Roebling decided to make the new structure of such width as to enclose the old one without disturbing the railway traffic thereupon. Consequently, the two halves of the arch were projected outward from the sides of the gorge by the cantilever method and joined at the centre with only minor adjustment. Not a train was delayed and highway traffic was held up only two hours each day during construction.

Great precision in the location of the two pairs of skewbacks, or end pedestals of the arch trusses, 550 feet apart, on opposite sides of the river, was necessary. In bridge work it is dangerous to make a measurement but once. Their centre points were fixed twelve or thirteen times with a maximum variation of only oneeighth of an inch, and when the semi-trusses were projected from opposite shores they were found to be in line within one-sixteenth of an inch. When the halfarches approached closure at the centre point, or crown, the lengths of the members required to fill the gap did not have to be modified, so accurately had the field measurements been taken. Further increase in traffic weights made necessary the extensive reinforcement of the bridge in 1919. This was carried out by Charles Evan Fowler.

Record-Breaking Steel Arch

\ fEANTIME, farther up the river but A»A a few hundred feet below the falls, stirring bridge history had been enacted To meet the needs of those who wished to cross the river at this point, a suspension bridge of 1,268-foot span with wooden towers and wooden floor had been built in 1868, according to the designs of Samuel Keefer. In Canada the Keefer-, through solid achievement, earned many years ago a place as a distinguished engineering family, comparable with that of the Stephensons in Great Britain Shown by traffic demands to be too narrow

—two vehicles could not pas bridge was widened in 1888. Within a month of the reconstruction, a tremendous gale swept up the gorge, tore loose one of the storm-stays from its anchorage and flung the swaying bridge into the river,

leaving nothing but the cables and the towers as a monument to the labors of eighteen months. With the spirit of the frontier, the directors met within forty-eight hours, ordered material, and in 117 days the bridge was once more ready for traffic.

Continued on page 42

Hazards of the “Sand Hog

Continued from page 13

Development of electric railway lines in the Niagara district made necessary the replacement of the rebuilt suspension bridge after a service of only seven years. In 1898 it gave way to the great upper arch bridge, which with its 840-foot span held the world’s record for an arch until replaced by the 977Trfoot Hell Gate arch at New York in 1917. Like the Grand Trunk arch, this great structure was cantilevered in halves out from the banks and met at the centre exactly as calculated.

While the suspension bridge and the arch have been the favored types for the Niagara gorge, a notable cantilever bridge was erected in 1883 by the Michigan Central Railroad alongside the Roebling suspension bridge. This structure contained the longest cantilever span erected up to that time in America, and was the second cantilever bridge to be built on this continent. Constructed for the rolling loads of forty years ago, it was reinforced for loads fifty per cent, greater in 1900, and due to the still mounting weight of traffic, it is to be replaced shortly by a great arch of 640foot span similar in form to the Grand Trunk arch. The new structure will be projected out from the rocky bluffs, temporarily supported by four corner backstays, each taking a pull amounting to 3,700,000 pounds at the moment of closure. Such a force would lift sixteen of the heaviest locomotives in use on the railways of Canada.

Above the falls, the only bridge so far constructed is the famous International bridge built in the early seventies between Bridgeburg and Black Rock. People said a bridge could not be built here. To this day it is the only structure crossing the Niagara River with piers in the stream. That such is the case is not remarkable, when it is remembered that the current even at this point normally runs at bVi miles an hour, and during high south-west winds may attain a velocity of twelve miles an hour. Ice floes, three feet thick, piling up against the work in winter, added further hazards. In the difficult work of placing and anchoring the caissons and carrying out the construction of the river piers, the chief credit was due the head of the contracting company, the late Sir Casimir Gzowski.

Wind Wrecks Queenston Suspension

AT THE end of the Whirlpool Rapids,

• between Queenston and Lewiston, two notable bridges have been built in succession on the same site. Captain Serrell constructed here, in 1850, a suspension bridge of 1,040-foot span which did duty until 1864. In that year an unusually severe ice jam made it necessary, as a matter of prudence to detach the storm-stays or wind-cables which held the bridge against wind uplift and extreme swaying. Unfortunately, these stays were not replaced promptly. A violent wind arose, and the suspended structure was wrecked. The swinging cables continued to hang on their towers until 1898, when they were removed to give place to the present fine suspension structure. Since the engineer is essentially a conservationist, it is characteristic to find that the wire from the cables of the Niagara Falls and Clifton bridge, then being replaced by the present upper arch, was used in the Queenston-Lewiston structure. It was in as good a condition as when new.

Traffic necessities between Ottawa and Hull, below the Chaudière, made the bridging of the Ottawa river inevitable. One of the great cantilever bridges of the country—the Alexandra, or Interprovincial, Bridge—was erected here in 1901. The prevailing industry of the region came curiously to the fore when it was found that the caissons for the great piers—some of them seventy-five feet deep—had to cut their way to rock through fifteen feet of sawdust and waterlogged slabs.

Many a bold enterprise has come out of the West and, in this, bridge-building is no exception. To shorten the line between Lethbridge and MacLeod, and at the same time to abolish, seven-degree curves and 1.2 per cent, grades, the Canadian Pacific Railway decided, as a result of extensive surveys conducted in 1904 and 1905, to construct a cut-off between these two points. A major feature of the proposal was the bridging of the Belly River. Rail level had to be 314 feet above the bed of the river, and the structure the longest of its kind in the world. However, the economics of the situation justified the building of such a giant trestle, and the great Lethbridge viaduct, the longest and the most massive, but not the highest, was completed in 1909. It is 5,328 feet long and contains 12,200 tons of steel. The huge 100-foot plate girders were hoisted and dropped into position like so many joists by a ponderous, long-armed traveller weighing when in working condition, 356 tons.

There are likely to be, as a matter of course, a number of fatalities in the building of any great structure. In spite of the dizzy height of the Lethbridge viaduct and the terrific winds that sweep through the valley, there were only two men killed. One fell from the top of a tower while making connections for steel work, and a stranger walking over the bridge, before the floor was completed, fell through. Two other men perished from gas in their efforts to rescue a boy who, contrary to orders, had gone down an exploration pit to some coal workings near a viaduct pedestal.

City bridges frequently possess interest for the observer by reason of aesthetic merit along with magnitude. The Bloor Street viaduct, Toronto, completed in 1918 at a cost of two and a half million dollars, is a structure in which finish and appropriate lines were given unusual attention. The rubbed granite surfacing of the concrete parapets has drawn universal commendation. Although none of the spans of this bridge is recordbreaking, the total length of the bridge is nearly as great as that of the Lethbridge viaduct and its width and traffic ■capacity enormously greater. The economic value of a great bridge to a community has been strikingly demonstrated in the amazing development, since the •completion of the Bloor Street viaduct, •of the section of Toronto east of the Don River.

World’s Greatest Span

ALTHOUGH the building of great bridges in Canada did not begin until some of the great bridge-building ■countries of the world had passed into decadence, this country is able to claim the longest and boldest span ever erected. There are those who would temper our pride in this possession by allusion to the losses of life and property that were incurred in the consummation of the enterprise. That modesty is fitting under the circumstances cannot be questioned, but we may at least be allowed the satisfaction of reflecting that Canadian engineers and Canadian industry met appalling accident and loss with steadiness and courage, and finally brought the project through to a triumphal conclusion.

The collapse of the original structure •during erection, in 1907, was due to an error in judgment. It was estimated that a certain type of great compression member ought to have a greater strength than it actually possessed. The loss of eighty lives and many millions of dollars in property was a terrible corrective, but engineers will never make that mistake again. Thus do we learn. We cannot expect that the judgment of the engineer will always be sound, any more than that of a general. What we do know, however, is that he will be right nearly 100 per cent, of the time.

In dropping of the suspended span of the new bridge during erection, in 1916, through the failure of a support casting, the unknown hazards faced by the engineer are again indicated. It is difficult to estimate the exact composition and condition of every piece of metal or concrete in a bridge, but the rarity of major accidents is an indication of how well the engineer meets this problem. So satisfied were the engineers of the Quebec bridge that their general plan of erection was sound that they proceeded to place the new span by the same method as that adopted for the lost one.

The Quebec bridge has a central span of 1,800 feet, ninety feet longer than each of the twin spans of the Forth Bridge, with which it is frequently compared, and fifty feet longer than the Delaware River suspension bridge now being erected at Philadelphia. One of its main piers is founded 101 feet below highwater level and it affords clear headroom of 150 feet to ships at extreme high water. From the lowest point of the deepest pier to the tops of the main posts, there is a range of 461 feet.

For risk to health, and perhaps to life, no occupation can compare with that of the “sand hog.” These men working under compressed air in slowly-sinking pneumatic caissons, which are, in effect, tremendously strong boxes without bottoms, remove the sand or other material to allow the caisson to sink to bed rock, or to something as good. This, then, forms the base on which the pier is built. At depths of 100 feet or so, such as those for the great piers of the Quebec bridge, the danger of “the bends,” loss of hearing, or paralysis is great. Formerly, on deep foundation work several men would lose their lives, but so complete were the arrangements at the Quebec bridge, that there were very few cases of serious injury, and no deaths. Men seized with “the bends” through coming out of a caisson too soon were taken quickly into a great steel hospital lock where they were subjected to the pressure from which they came, and then through easy stages down to atmospheric pressure. A man coming from a depth of 100 feet was required to take twenty-five minutes in doing it, and if he took less he ran serious risks; even then, he was allowed to work only two one-hour shifts in the twentyfour.

The most heavily-loaded member of the Quebec bridge was proportioned for a stress of 29,583,000 pounds, while the maximum load on the .base of a main pier may be as much as 192,000,000 pounds. The main pins, or great connecting bolts, at the base of the tall posts over the main piers are thirty inches in diameter—the largest ever built. There are 66,480 tons of steel in the bridge, while the Forth bridge with its two 1,710-foot spans and approach spans combined contains only 57,000 tons. The Quebec bridge will accommodate 2.3 times the live, or moving, load that the Forth bridge will carry, and it weighs 2.2 times as much per running foot. The steel employed, however, per pound of moving load to be carried, is ten per cent, less than for the Forth bridge. Thus has the art of bridge design progressed.

Monumental Concrete Bridges

REINFORCED concrete is not adapted to the construction of the extremely long spans that become possible through the utilization of structural and alloy

steels as main material. Nevertheless, within the limits of this form of construction, bold and imposing bridges have been built in Canada. For structures in which the aesthetic element plays an important part, and for those of a monumental character, concrete is invaluable.

Extremes of temperature in Western Canada impose unusual difficulties on the builder of concrete bridges. Not only must he ensure that the wet concrete be not frozen—which would mean its inevitable undoing—but large changes in dimensions due to expansion and contraction must be fully met.

Difficulties of this kind were encountered and successfully overcome in building University bridge at Saskatoon. The piers could be, and were in part, constructed in cold weather, across a frozen river, although such work was rigorously avoided in January and February. The risk was too great to take chances of freezing in a work of this magnitude and importance. The great arch rings, four of them of 150-foot span, were left entirely for summer construction. Probably no structure has ever been built with greater precautions against rupture from extreme temperature effects. The range assumed was from fifty degrees below zero to ninety above. In certain arches of this bridge, possible stresses due to temperature variation were provided for to amounts in excess of the sum of all the other stresses combined.

Calgary has reason to be proud of her fine concrete bridges. They are amongst the most notable in the country. The largest, the Centre Street bridge, contains three 150-foot spans with traffic on two levels. In keeping with the construction of most western bridges, unusual hazards of frost and flood had to be overcome. Work on one of the piers had to be discontinued in January after the \ temperature dropped suddenly to forty-six below zero. The city engineer, George W. Craig, and City Commissioner Garden were inspecting the work in its early stages when the Bowr River, swollen by flood, carried away the temporary bridge on which they were standing. Mr. Craig managed to scramble to shore, but Commissioner Garden was carried away by the torrent and, after being picked up by boatmen, was landed on an island a mile below the bridge. Even bridge inspecting has its hazards.

Art and Engineering

UNUSUAL efforts were made to blend the utilitarian and the artistic in the new Ashburnham bridge at Peterborough. It affords an instance of the wise cooperation of engineer and architect on monumental structures. The main arch span of this bridge is the longest of its kind in Canada—234 feet between springings. Spandrel arches, that is the minor arches superimposed on the major one, vary in span in accordance with the distance from the crown of the great arch, with an effect that is undoubtedly happy. The fact that on this particular work the engineer and the architect became associated through their common interest in the theory of relativity, did not militate against the success of their professional labors.

The fields of endeavor in which Canadians have excelled are many, but in the counting, bridge building should not be overlooked. Problems that had to be solved and hazards that had to be met in this sphere have been encountered and dealt with effectively and decisively. There are no bridge-building enterprises too big for Canadians.