I will not weary my readers with the enumeration of all the experiments to be made on the tower, of which a programme has been already drawn up by our scientific men, and which include the study of the fall of bodies through the air the resistance of the air to varying velocities, certain laws of elasticity, the study of the compression of gases of vapors under the pressure of an immense manometer of 400 atmos pheres, a new realization on a great scale of Foucault's pendulum demonstrating the rotation of the earth, the deviation toward the East of a falling body, etc., etc.; lastly, a series of physiological experiments of the deepest interest. I may even go so far as to say that there are few scientific men who do not hope at this moment to carry out, by the help of the tower, some experiment connected more especially with their own investigations. Thus it will be an observatory and laboratory such as was never until now at the disposal of science; and from the first all our scientific men have encouraged me with their warmest sympathy. On my side, and in order to express in a striking manner that the monument which I have raised is dedicated to science, I decided to inscribe in letters of gold on the great frieze of the irst platform, and in the place of honor, the names of the greatest men of science who have honored France, from 1789, down to our own day. Besides all these uses, which I might have explained in greater detail, but which, even in this rapid summary, will serve to show that we have not erected an object of barren wonder, the tower possesses in my eyes a usefulness of a totally different order, which is the true source of the ardor which has inspired me in my work. The public at large understood this, and it is also the reason of the very general and warm sympathy which has been displayed toward me. My object was to show to the whole world that France is a great country, and that she is still capable of success where others have failed. The Scientific American said, in 1874, with reference to the tower of Philadelphia, destined to celebrate the centenary of the national independence: "The character of the project is closely connected with the purpose of its erection; the hundredth anniversary of our national existence ought not to be allowed to pass without a permanent memorial, which an exhibition lasting a few months cannot furnish. It is evident that in the space of two years no monument of imposing aspect and original in conception can be constructed with other material than iron; from every point of view we could not choose a more national construction. We will celebrate our centenary by the most colossal iron construction that the world has seen." Can we not apply to ourselves these words which, remaining a dead letter in America in 1874, have become for us in France a living reality! May I be allowed to recall here a few words which I pronounced in inaugurating the first stage of the tower, and which sum up my ideas on the subject: "The beginning was difficult, and criticism as passionate as it was premature was addressed to me. I faced the storm as best I could, thanks to the constant support of M. Lokroy, then Minister of Commerce and Industry, and I strove by the steady progress of the work to conciliate, if not the opinion of artists, at least that of engineers and scientific men. I desired to show, in spite of my personal insignificance, that France continued to hold a foremost place in the art of iron construction, in which from the earliest days her engineers have been more particularly distinguished, and by means of which they have cov ered Europe with the creations of their talent. Doubtless you are not ignorant that almost all the great engineering works of this nature, in Austria, Russia, Italy, Spain, and Portugal, are due to French engineers, and the traveller discovers with pride, as he passes through foreign countries, the traces of their activity and their science. "The tower, 1,000 feet high, is before everything a striking manifestation of our national genius in one of its most modern developments; and this is one of the principal reasons for its existence. If I may judge by the interest which it inspires, abroad as well as at home, I have reason to believe that my efforts have not been unavailing, and that we may make known to the world that France continues to lead the world, that she is the first of the nations to realize an enterprise often attempted or dreamed of: for man has always sought to build high towers to manifest his power, but he soon recognized that the laws of gravity hampered him seriously, and that his means were very limited. It is owing to the progress of science, of the engineer's art, and of the iron industry, that we are enabled to surpass in this line the generations which have gone before us by the construction of this tower, which will be one of the characteristic feats of modern industry." So it is that I have wished to raise to the glory of modern science, and for the more especial honor of French industry, a triumphal arch as striking as those which earlier generations have raised to honor conquerors. THE EIFFEL TOWER.* By WILLIAM A. EDDY. A tower about 1,000 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 be yond 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 trestlework 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 construction 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 cen timeter 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: 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 *From the Atlantic Monthly, June, 1889; vol. LXIII, pp. 721-727. 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 demo. lition, part of the base was re-constructed 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 original 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 top. most 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 stone work to a height of 1,000 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 450 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 Bastile one hunH. Mis. 224-47 dred 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, and are connected 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 centimeter 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 9 pounds for each square centimeter, 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 lattice-work. 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 |