The Highest Structure in the World

A TOWER about one thousand feet in height was first thought of during the organization of the Centennial Exposition at Philadelphia, in 1876, and its possible construction was discussed in the newspapers at the time. But consultation with engineers and architects probably resulted in the conviction that the scheme was impracticable, and the expense beyond the value of the investment, especially if masonry were used. Aside from the question of outlay, a serious difficulty in the construction of any kind of material to such an altitude, there are questions of pressure and danger that daunt experienced engineers. M. G. Eiffel, constructor of some of the greatest works in France, notably the trestle-work viaduct at Garabit, 407 feet high, concluded that the building of such a tower had not been attempted in ancient times, so far as known, because iron then lacked the lightness, strength, and adaptability seen in modern work. The enormous weight of masonry in so great a mass would not only imperil, by its tremendous pressure, the courses of stone near the ground, but would cause an irregular settling of the foundations, as in the well-known instance of the Leaning Tower of Pisa. In modern work, a pressure of 66 pounds for each square centimetre¹ is considered dangerous. It is admitted that 55 pounds in this proportion is too extreme for safety, although, owing to peculiarities of construction, this has been exceeded in some of the following instances cited by M. Navier : —

Pillars of the dome of the Invalides, Paris, 32.55 pounds.

Pillars of St. Peter’s, Rome, 36,08 “

Pillars of St. Paul’s, London, 42.70 ”

Columns of St. Paul-hors-les-

Murs, Rome, 43.58 ”

Pillars of the tower of St.

Merri, Paris, 64.85 ”

Pillars of the dome of the

Pantheon, Paris, 64.94 ”

M. Navier includes an estimate of 99.25 pounds for the Church of La Toussant à Angers, which is in ruins, and so not a convincing example. It thus appears that the resistance in some daring structures is from 33 to 44 pounds, and only rises to nearly 65 in two instances. M. Eiffel cites the Washington Monument, which in its simplicity and boldness he considers remarkable. In M. Navier’s estimates given for the greatest feats of architectural engineering in the Old World, this huge obelisk stands high on the list of wonderful structures, the pressure at its base amounting to 58.35 pounds in the proportion above given. With the exception of the Eiffel tower, it is easily a bolder undertaking than any other of its kind known in the world, because it stands upon a relatively small base, with no side support, with a weight upon its foundations of 45,000 tons. This immense square shaft, about 55 feet on a side, served as an illustration of the danger in attempting to carry masonry to a greater height than before achieved. Fortunately, the foundation settled evenly, but to prevent probable demolition part of the base was reconstructed and filled in with concrete. Meantime the structure began to lean to an extent that caused great uneasiness, and finally the suspension of the work. The construction was begun in 1848, and in 1854, when it reached a height of 152 feet, its dangerous condition became somewhat marked. Its originally intended altitude of 600 feet was then reduced to 500. In 1880, after great difficulties, the base had been widened and the foundation enlarged and deepened. Work was then recommenced, and the masonry continued upward at the rate of about 100 feet yearly, until the topmost stone was laid December 6, 1884. The inauguration took place February 21, 1885.

An additional source of peril in the use of masonry, not included in the danger of settling, as in the Washington Monument, is the insufficient adherence of modern mortar to great masses of stone, causing serious crumbling, and a reputation for danger much to be dreaded. An attempt to extend stonework to a height of one thousand feet would cause an expense too great for the end attained, and the danger of fracture would be incessant and unavoidable. It seems that we can excel the ancients very little in the treatment of masonry. There is no easily discovered evidence that they built any such structure higher than the great Pyramid of Cheops, originally 480 feet in height. They had good reasons for this caution. If the foundations are solid, the stone may disintegrate, owing to the unequal distribution of the enormous weight, due to the limited power of the mortar to act as a cushion to equalize the force. The Egyptian and other ancient builders constructed some masonry without mortar by polishing and closely fitting the stone, but it is not probable that they tried to carry such work to a very great height. In some modern buildings it is found that the resistance of very hard stone increases that of the mortar. Stone or brick work might reach a higher point than the Eiffel tower by the invention of cements more efficient than any now known.

In considering the important question of the foundations for this great tower, elaborate borings were made in the Champ-de-Mars at Paris. This is a level field or park, about two thirds of a mile long and half as broad, devoted usually to the drilling of troops and to reviews, upon which the Exposition buildings for 1889 are now approaching completion, in commemoration of the storming of the Bastille one hundred years ago, July 14 and 15, 1789, that memorable event of the French Revolution. It is intended to show the great advances in science, art, and industry since that crude attempt to establish a republic.

In selecting this location near the river Seine, much thought was given to the question of a foundation, because even a slight giving way would be so magnified in the great height of the structure that the strain sustained by cross-pieces and braces would be far greater than calculated. Fortunately, it was found that the soil consisted of a compact bed of plastic clay, 53 feet in thickness, surmounted by a bank of sand and gravel, and all inclined toward the Seine. This seemed well fitted for the purpose. M. Eiffel was not, however, entirely satisfied with it. He therefore increased the solidity of the foundations by means of caissons (heavy iron boxes with open bottoms) of compressed air, which made their way downward into the soil partly by their own weight and partly by the excavation of the earth beneath them. The air prevented the possible rising of soft clay to smother the workmen. Incandescent electric lamps furnished light beneath the caissons, which were filled with heavy concrete that hardened, making as it were huge bricks of great solidity that sank still deeper. It was owing to this modern device, the compressed-air caisson, that a great danger was averted. The remains of unquestionably ancient masonry were found, which might have caused a dangerously uneven settling of the foundation. At each corner of the tower, which is square at the base and about 300 feet on a side, there is a lattice-work pillar that slants inward as it rises upward to a distance of about 600 feet from the ground, from which point the four like pillars continue together to the summit. These corner pillars are each 50 feet square at their bases, which are separated by open curved arches. Any unimportant subsidence of the foundation is provided for by hydraulic presses applied to iron wedges that lift each corner of the entire structure, and so any defect or strain due to contraction or expansion can be regulated. The relative lightness and strength of the material is such that the total weight will not be more for each square centimetre than that of a usual five-story house, certainly not as great as in very high buildings in New York and other large cities. The pressure upon the base of the tower is not more than nine pounds for each square centimetre, while in the case of the Washington Monument it is, as we have seen, more than 58 pounds in like proportion.

The foundations became practicable, but there was a powerful and irregular force involved in the tremendous side pressure of the wind upon a tower presenting so much vertical surface in spite of its open latticework. It is evident that the height of the great Washington Monument has been surpassed only by the use of iron, which has the power to bend and still resist the force of the wind, and which is well able to withstand marked contractions and expansions. The horizontal vibration is considerable under a high wind, at such a distance above the earth. The swaying of the long curved uprights will not be felt much by people at the summit. The height of the tower is such that the nature of the motion is gradual and less observable than in light-houses constructed of masonry, in which the elasticity is sometimes remarkable, owing to the quality of the mortar used. It is in recent years only that metallic beams have been made that enable engineers to erect structures to a height of 200 feet. Still further advances in the manufacture of iron make it now easy to attain 250 or even 350 feet. So many unknown quantities require consideration in a tower 1000 feet high that the problem becomes serious and hard to solve. M. Eiffel points out the significant fact that the obstacles resemble those met with in extending a bridge from 500 feet to twice that distance horizontally, because of the great and accumulating side pressure of the wind exerted upon high vertical structures. It is thus seen that the construction is a greater achievement than would be at first imagined. It was desirable, while estimating the tremendous wind pressure, to avoid the multiplication of upright beams, involving diagonal braces more than 300 feet in length, which would result in an immense ugly iron framework resembling an elongated cage, or trestle-work railway bridge set up on end, with a deplorable architectural effect. Clumsy masses of beams and braces were necessarily omitted. The curved lattice - work before mentioned disposed of this question.

The corner pillars narrow from about 50 feet on a side at the base to 16 feet near the summit. They are anchored upon solid foundation walls, and bound together by horizontal girders, which serve as supports for several large halls or assembly rooms at different heights. These floors increase the security of the structure. The uncertainty of the wind force and its extent as calculated has led M. Eiffel to be peculiarly prudent in his methods of construction. He assumes for purposes of safety that the force goes on increasing from the base to the summit until the pressure is doubled. In making estimates of resistance, the iron lattice work was considered a solid wall taking the full force of the wind. In the more open parts of the tower, the actual surface of the iron was multiplied by four to secure safety from the effects of a severe tempest. The wind in Paris ordinarily exerts a strain of from 13 to 15 pounds for each square metre.² A pressure of 22 pounds is allowed for in Germany and Austria, in metallic frameworks not subjected to the tremors of passing trains. This rule also holds in France. But it becomes necessary to provide for a much severer strain when only one end of the structure is supported, as in the Eiffel tower.

The inclination of the stone-work supporting each corner is at an angle of 50°. In extending upward the slanting ponderous iron-work it was very difficult to maintain absolute stability, especially before the masses had been made secure by girders at the first gallery. As the work progressed, this danger of displacement, requiring the utmost care, was lessened by the decreasing length of the girders that bound the whole together. In high trestle-work the apparently slight metallic bars seem insecure to the casual observer, an effect peculiarly noticeable in the high skeleton iron-work of the Manhattan Elevated Railroad near Eighth Avenue and 110th Street, New York city. The spindling framework in this case suggests weakness, but this is an illusion due to an association of strength with the ponderous solidity of masonry or earth-work.

The tower is spread much at the base, to enhance its stability. Perhaps its height is exaggerated by the distant view of buildings in the Exposition grounds. The first gallery, which consists of an immense hall, is to be used as a promenade or for restaurants. It is 230 feet from the ground. Still further up is the second gallery, about 100 feet square and at a height of 377 feet, which exceeds the altitude of the following well-known structures : —

The dome of Milan, 363 feet.

Spire of the Invalides, Paris, 342 ”

Spires of St. Patrick’s Cathedral, New York, 332 “

Statue of Liberty, New York Harbor (above the water), 328 “

Brooklyn Bridge towers, 278

Continuing up the Eiffel tower until it has narrowed to about 75 feet on a side, we come to a point where the four great pillars combine at about the height of the great Washington Monument, the next highest known structure in the world. Only three of the following public edifices, aside from the greatest of the Egyptian pyramids, are more than half as high as the Eiffel tower: —

Washington Monument, 555 feet.

Cathedral of Cologne, 522 “

Old St. Paul’s, London (destroyed by fire), 520 “

Cathedral of Rouen, 492 “

Pyramid of Cheops, 480 “

Cathedral of Strasbourg, 465 “

Cathedral of Vienna, 453 “

St. Peter’s, Rome, 432 “

Present St. Paul’s, London, 404 ”

After adding 306 feet to the height of the Washington Monument, making 861 feet, the third gallery of the Eiffel tower is reached, where there is a glassinclosed room 32 feet square, surrounded by a balcony. Surmounting this and 124 feet higher is a small observation room, with two windows on a side, from which can be seen Paris and its environs for a radius of about 75 miles.

The elevators, four in number, are to be worked in pairs, — two to be used for visitors ascending, and two for those descending, that an incessant stream of people may move in each direction. The ascent is to be made no faster than 20 inches a second, because great speed in stopping and starting would be decidedly alarming and disagreeable.

The escape of lightning is to be provided for by two cast-iron conducting pipes about 20 inches in diameter, reaching from the summit to the base, and thence 60 feet into the ground.

The construction of a tower composed of curves that will best withstand the wind has produced a very graceful architectural outline. The air of trimness in the realization of the design is due to the fact that there has been no waste of material. An upward moving force in taking the direction of least resistance would doubtless assume approximately the form of this structure. Nearly all kinds of growth acquire something like this cone shape while manifesting concentrated motion necessitated by surrounding forces. Many beautiful designs are founded upon the tapering forms of flowers and leaves, as in the delicate tracery of frost-work. In building to secure safety from the action of the elements, M. Eiffel has perhaps unintentionally followed the methods of nature, and thus the architectural beauty of his work has the best possible confirmation.

The well-worn criticism that this scheme lacks utility is ever present in all daring scientific enterprises. But the value of this tower is admitted by eminent French scientists. It will take the place of the great balloon let up into the air by means of a cable worked by steam, which was so successful during the Exposition of 1878. An ascent can be made without the danger of collapse or gas explosion caused by lightning, often present in a captive balloon. The unexpectedly rapid approach of a local storm might cause loss of life before the winding-in of a balloon could be completed. The view of Paris at night, with its seemingly interminable boulevards brilliantly lighted, is marvelous, and such as aeronauts only have experienced. The feeling of distance and height will not be lessened by intervening lower slopes, as in most mountain views.

It is proposed to put upon the tower a number of electric lamps, powerful enough to light the city. The advantage of such a system had been long thought of, but it was a very difficult project to carry out, owing to the great intensity necessary. It has been decided, however, that the Exposition buildings and grounds are to be lighted in a manner never before equaled. In 1881, M. Sebillot proposed to place electric lights at an elevation of 1000 feet, but the idea involved difficulties of construction and a waste of illumination that made it impracticable. It has been found that to make printed matter sufficiently legible in the park and gardens of the Exposition, not less than three concentric zones, numbering 48 lamps, would be required at so great a height. With special reflecting mirrors concentrating the light within prescribed limits, it is believed that the effect would be better than anything before accomplished so far as known.

Many eminent men promptly admit the value of the tower for scientific purposes. M. Hervé - Mangon, of the Meteorological Society of France, points out the importance of observations made at different distances from the earth’s surface under these conditions, and that experiments of the greatest interest are possible. The law of the decrease of the temperature with the height would be demonstrated better than from high points of land or from vast structures of masonry, which retain much heat, causing currents of air that interfere with observations or make them inexact. The variability of rainfall could be well observed, also the average height to which fogs reach above the earth’s surface near Paris. A relatively complete knowledge might be gained of the volume of water held in a globular condition in different air strata. This would make clear the reason why clouds light in volume sometimes precipitate so much water. As the condition of the air varies with the height, the advantage of having instruments far enough apart, one above the other, is obvious. On calm days, the general direction of the wind would be free from the effect of local heat accumulation due to the influence of neighboring buildings. All these phenomena could be carefully observed at a height to which only balloons ascend for an appreciable length of time. At this distance from the ground, the atmospheric conditions, freed from the surroundings of a mountainous or hilly region, are not precisely known.

A position above the fogs that very often obscure the horizon of Paris will facilitate astronomical observations impossible in ordinary weather. The vibration of the tower will doubtless exclude it from use in obtaining the precise positions of the stars, as pointed out by some astronomers, but it will leave the field free to researches regarding the chemical constituents of the stellar universe. Observations intended to establish the proper motions of stars by the displacement of lines in the spectrum would be more exact at a height of 1000 feet than at that of the observatories. Photographic apparatus at the summit of the tower would be more efficient in case of an eclipse near the horizon, but work upon stars or nebulæ, requiring steadiness of position, ought to be reserved for calm nights. In every case the moon and the planets could be studied and drawn under more favorable conditions. The known temperature of the air at different heights is also of great importance in astronomical observations, because the resulting variation in refraction is so often a matter of conjecture.

In addition to the above experiments in meteorology, electrical science, and astronomy, there remain to be considered further questions of vegetable chemistry, peculiarities of growth under various conditions, and more exact data respecting the material constituents floating in the air. Further and finer investigations can be made, showing with additional interest the value of Foucault’s well-known pendulum experiment demonstrating the rotation of the earth. The distinction between magnetic attraction and gravitation, which Faraday investigated with a falling body, might be carried further with advantage.

The instantaneous transmission of time signals for the benefit of all Paris, the more exact measurement of the velocity of sound under various atmospheric conditions, the estimated resistance of the air as a body falls at given rates of speed, the law of metallic elasticity in the contraction and expansion of the iron-work of the structure, the study of compressed gases and vapors with such extensive vertical possibilities, — these are some of the objects to be attained by this tower, destined to be one of the landmarks of scientific advancement. It may be of use as an army signal station in case of war, as a position from which to observe the movement of an enemy. At a time of siege or of interruption to telegraphic communication, the tower could be used as a centre for optical military signaling for long distances, such as the 70 miles from Paris to Rouen. In such instances an answering signal might be sent from a high hill near at hand.

The immense outlay of work in this great structure cost only 6,500,000 francs, $1,300,000. There are 27 iron panels, each of which required a separate diagram, that in turn formed the basis of a series of geometrical designs calculated by means of tables of logarithms. The metallic pieces number about 12,000, and the position of each and the places for its rivets had to be decided without error. In the iron plates were drilled 7,000,000 holes, which if placed end to end would form a tube 43 miles long. There were 500 engineers’ designs and 2500 leaves of working drawings. It was necessary to employ 40 designers and calculators for a period of about two years. It is thus seen that the iron forms a vast complicated network, not easily realized when contemplating the gracefulness of the completed tower. The large halls at Levallois-Perret had almost the appearance of a government administration.

M. Eiffel did not employ workmen of special skill, accustomed to very high scaffolding. It was feared that few could be found not subject to vertigo. But in the tower they did not work high in the air, with an open and dangerous footing. They were on platforms 41 feet wide, and as calm as on the ground. It is proper that two great republics should, regardless of nationality, recognize the constructive genius of M. Eiffel, as they have already done in the instance of M. Bartholdi, designer and constructor of the wonderful statue of Liberty Enlightening the World. Mr. Roebling’s great work, the Brooklyn Bridge, thus seems extended into new conditions. The idea of a tower 1000 feet high first assumed definite form, it will be remembered, in the United States, and it remained for a man of constructive genius in another and newer republic to crystallize it into an accomplished fact.³ The power of thought over the refractory materials of the earth, as shown by the ingenuity of Thomas A. Edison, a power which Emerson illustrated in various ways, is thus emphasized anew. The limits of scientific achievement slowly recede.

William A. Eddy.