332 REPORT ON NATIONAL MUSEUM, 1886. 



a sunny day, so that a pendulum suspended from the center of the top 

 describes an irregular ellipse nearly half an inch in greatest diameter.* 



Under such circumstances as these it is not at all strange that many 

 stones show a decided weakening and tendency to disintegration after 

 long exposure, and particularly on those sides of buildings exposed 

 lougest to the sun, and which are, therefore, subject to the full range of 

 temperature variations. Professor Julieu has called attention to the 

 marked decay thus produced on the western face of the tombstones in 

 Trinity church-yard and elsewhere. It is stated further that the ashlar 

 base of the steeple of the church at Thirty seventh street and , Fifth 

 avenue, New York City, is beginning to exfoliate from this cause on 

 the south side (where the sun shines the longest) but not on the north 

 and east. Other examples are seen on the stone stoops of the east and 

 west streets, where the western face of the dark-brown sandstone is 

 badly disintegrated and exfoliated, while the eastern face remains much 

 longer in a perfect condition. The author has observed similar effects, 

 but in a less marked degree, on the Smithsonian building, at Washing- 

 ton, D. C. The south and west sides frequently show exfoliation, while 

 the north and east, upon which the sun shines but a small portion of 

 the day, are almost untouched. 



This same expansion and contraction of stone sometimes produces 

 disastrous effects other than those of disintegration within its own mass. 



The difficulty of obtaining permanently tight joints even with the 

 strongest cements led Colonel Totten to institute a series of experi- 

 ments with a view to ascertain the actual expansion and contraction of 

 granite, sandstone, and marble when subjected to ordinary tempera- 

 tures. Upwards of thirty experiments on each of these varieties of 

 stone showed the rate of expansion and contraction, which seemed to 

 be uniform throughout the range of temperatures employed, to be for 

 granite .000004825 inch per foot each degree Fahrenheit : for marble 

 .000005GG8 inch, and for sandstone, .000000532 inch.t 



Supposing, then, two coping stones each 5 feet long be laid in midsum- 

 mer at a temperature of 90° Fahr. In winter the temperature falls to 

 zero, a change of 96°. If the stones contract toward their centers, the 

 whole length of stone put in motion will be 5 feet. In the case of gran- 

 ite, then, the shrinkage amounts to .027792 inch, in marble .032G4 inch, 

 and in sandstone to .054914 inch. This shrinkage, small as it seems, 

 from necessity gives rise to cracks at the joints, which admit the pas- 

 sage of water; continual shrinkage and expansion must in time crum- 

 ble the cement and leave the joint permanently open.J 



The effects of moderate temperatures upon stone of ordinary dryness 

 are, however, slight when compared with the destructive energies of 



* Dana, Manual of Geology p. 720. 



t Adie found the rate of expansion for granite to bo .00000438 inch, and for white 

 marble, .00000613 in.— Trans. Roy. Soc. Ediu., xni. p. :\W. 



fW. IT. C. Bartlett on Contraction and Expansion of Building Stone. Am. Jour. 

 Sci.,Vol. xn, 1832, p. 13G. 



