February 20, 1885.] 



SCIENCE. 



149 



corrected. The area of the foundation was 

 increased 150 °/ 0l or from 6,400 square feet to 

 16,000 square feet, and was carried down to 

 21.5 feet below the original surface of the 

 ground. Careful levels showed, that, during 

 the process of underpinning, the base of the 

 monument settled two inches. 



The foundation was further strengthened, 

 and the pressure distributed over the whole of 

 the new base, by placing a continuous buttress 

 of concrete around the base, from the top of 

 the old foundation halfwa} r out on the concrete 

 base ; a portion of the foundation masonry be- 

 ing cut awa}^, as shown in the sketch, to give 

 a good bearing. A terrace of earth was after- 

 wards added, to cover the rough masonry, and 

 to still further increase the depth to which the 

 foundation was carried, and thus to increase 

 the resisting-power of the ground against lat- 

 eral displacement. 



The new foundation was completed in Ma} r , 

 1880 ; and on Aug. 7 President Hayes as- 

 sisted in laying the first new stone on the shaft. 

 On the new portion the space inside was en- 

 larged from 25 feet square to 31.5 feet square, 

 to diminish the weight by lessening the thick- 

 ness of the walls ; and solid granite backing, 

 in two-feet courses to correspond with the out- 

 side marble courses, was substituted for the 

 irregular rubble- work. When the wall grew 

 considerably thinner, marble was used through- 

 out. The thickness at 500 feet is 18 inches. 

 The monument rose 26 feet in 1880, 74 feet in 

 1881, 90 feet in 1882, 70 feet in 1883, and 90 

 feet, to which was added the apex of 55 feet, 

 in 1884. 



Eight iron columns rise in the interior, shown 

 by small circles on the plan of the top. Four 

 of them are far enough from the wall to sup- 

 port the iron platforms and stairways by which 

 the monument may be ascended : the other 

 four act as guides for an elevator. These 

 columns have been connected with the water- 

 bearing stratum below the monument, and with 

 the metallic point on the apex. 



Several ways of capping the monument, or of 

 constructing the apex to suit its exposed posi- 

 tion, and secure permanence, were discussed. 

 The adopted design was by Bernard R. Green, 

 civil engineer. Three stone corbels, one foot 

 thick at the edge, begin to grow out from each 

 side of the well within the monument, at a 

 point thirty feet below the top of the wall. 

 They increase in width as they ascend, until 

 at the top of the wall the middle one projects 

 six feet, and the side ones four feet and one- 

 half each. From them spring stone arched 

 ribs, which in turn support the roof-covering 



of stone slabs seven inches thick. The middle 

 ribs rise thirty feet, and intersect on a cross- 

 shaped keystone ; the side ribs abut against 

 one another, and a square stone frame some 

 seven feet lower down. The apex is termi- 

 nated by an aluminium point. 



After the main walls had reached their ulti- 

 mate height, a frame carrying a derrick mast, 

 which reached to a height of 75 feet, was 

 erected on the tops of the iron columns. An 

 opening was left in the lower roof- course at 

 one side ; the stone for the roof run out on a 

 small balcony supported by projecting beams, 

 and then raised to place. When all but three 

 roof-courses were set (in all, some 14 feet in 

 height) , a platform was built around the top, 

 supported on brackets resting on the slanting 

 sides of the roof, and carried, in turn, on 

 beams projecting through the apertures for 

 observation left in the lower part of the roof, 

 two on each side ; and the nine remaining 

 stones were distributed on this platform. The 

 central derrick was then removed, and a small 

 quadruped derrick erected on the platform and 

 over the point of the roof. Thus these stones, 

 including a cap-stone weighing 3,300 pounds, 

 were readily set, and the apex completed Dec. 

 6, 1884. A small opening near the top, after- 

 wards closed by a stone slab, permitted the 

 retreat of the workmen who removed the scaf- 

 folding. 



Since the completion of the foundation, and 

 the resumption of building the shaft, some 

 slight settlement has taken place, increasing 

 regularly and uniformly with each addition of 

 a few courses of stone. After a few weeks 

 from any suspension of building, settlement 

 has always ceased ; and hardly a perceptible 

 movement again occurred until after some 200 

 tons' weight had been added, when the same 

 process of settling was repeated. Altogether, 

 in the addition of 400 feet in height, and about 

 34,000 gross tons, 12,000 tons of which are 

 in the earth terrace over the foundation, the 

 settlement was two inches. The entire settle- 

 ment, due to underpinning the foundation and 

 completing the superstructure, is about four 

 inches. The movements of the plumb-lines, 

 of which there were two, — one from the height 

 of 148 feet, and the other from 259 feet, — were 

 but trifling. Changes in them were infrequent, 

 and probably not alwa} 7 s, if often, due to actual 

 leaning of the shaft. 



The workmen were protected against injury 

 from falling b} 7 a strong net suspended around 

 the outside of the shaft ; and, since the resump- 

 tion of construction by the United States, the 

 onl}- accident has been the breaking of the 



