310 



ENGINEERING. 



largely disappears when the railroad takes the 

 place of the caravan ; but as a stimulant to 

 native industries it must in the course of time 

 prove highly effective. The line was formally 

 opened on the anniversary of the Czar's coro- 

 nation, May 27, 1888. 



The Eiffel Tower. This superb work was so 

 nearly complete at the end of the year that its 

 construction may be regarded as an accom- 

 plished fact. As a feature of the great Paris 

 Exposition of 1889, it is certain to attract a 

 large share of attention. The illustration is 

 from a perspective drawing made by M. Hanin, 

 of Paris, with a view to representing the tower 

 exactly as it will look when finished. Pho- 

 tographs will of course distort the propor- 

 tions even under the most favorable conditions. 

 On December 31 the structure was about 800 

 feet high. The total height is to be 984 feet. 

 It is intended merely as an ornamental observa- 

 tory, though some important scientific observa- 

 tions may be made from its summit. The 

 progress during the latter part of the work 

 averaged 36 feet a week. In comparison with 

 the Eiffel Tower, the heights of other lofty 

 structures are of interest. Washington Monu- 

 ment, 555 feet; Cologne Cathedral, 512 feet; 

 Strasburg Cathedral, 466 feet; St. Stephens, 

 Vienna, 443 feet ; St. Peter's, 433 feet ; St. 

 Paul's, 404 feet. 



The Garabit Viaduct. Among engineers M. 

 Eiffel's reputation will gain more from the via- 

 duct near Garabit, France, than from the Paris 

 tower. The central arch of the viaduct is 540 

 feet span, and rests upon two large piers, the 

 metallic part of which is 195 feet high. The 

 total weight of the arch is 2,608,540 pounds. 

 Cables were, of course, used to support the 

 two parts of the arch. M. Eiffel found by ex- 

 periment that an increase of half an inch in 

 the length of the cables increased the tension 

 2,200 pounds. By introducing a half-inch 

 wedge under the end of one of the cables, the 

 neighboring cables were decreased in tension 

 2,200 pounds, distributed over the other cables 

 as a whole. These latter, therefore, were con- 

 tracted to an extent corresponding to such 

 diminution of tension, and they consequently 

 raised the arch. The totalization of the slight 

 liftings due to the repetition of this manoeuvre 

 on each of the cables finally effected a general 

 lifting of four inches. When it was desired to 

 lower the arch, the operation was just the con- 

 trary, that is to say, the wedges were removed 

 in succession. 



After the two halves of the arch had been 

 brought so close together that there was room 

 only for the insertion of the center-piece, the 

 process of keying was begun. As the two 

 halves had, during the mounting, been held a 

 little above their final position, there was a few 

 inches more space between them than was 

 necessary for the insertion of the key, and it 

 was only necessary to remove progressively a 

 few wedges to bring the parts into contact. 



This operation was effected with such pre- 



cision that the key of the extrados was driven 

 home with a few blows of the hammer, a won- 

 derful instance of accurate calculation, consid- 

 ering the enormous size of the parts. 



In April, before the viaduct was opened for 

 travel, two tests were made, one with a sta- 



FIG. 12. HANDHOLE DISTRIBI'TION, BROADWAY, NEAR 

 EXCHANGE PLACE. 



Showing trench, manhole, handholes, distributing duct, and service-pipe. 



tionary load of 405 tons, and the same load 

 moving. The deflection in the first instance 

 was - 27 inch, and in the second 0'46 inch. 



Subways for Electric Wires. The multiplication 

 of overhead electric wires in the streets is so 



FIG. 13. MANHOLE. METHOD OF HANDLING CABLES. 



objectionable that measures have been taken 

 in most of the world's great cities to place 



