738 THE EIFFEL TOWER. 



dred years ago, July 14 aud 15, 1789, that memorable event of the 

 French Kevolution. It is intended to show the great advances in sci- 

 ence, 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 com- 

 pact bed of plastic clay, 53 feet in thickness, surmounted by a bank of 

 sand aud gravel, aud 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 whicb made their way downward into the soil partly by their own 

 weight and partly hy 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 founda- 

 tion. At each corner of the tower, which is square at the base and 

 abput 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, aud so any defect or strain 

 due to contraction or expansion can be regulated. The relative light- 

 ness and strength ef 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 u]ion 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 aud expansions. The horizon- 

 tal vibration is considerable under a high wind, at such a distance 



