TRANSACTIONS OF THE SECTIONS. 539 



and supplied it in some others from my own experiments ; 

 reckoning the modulus in lbs., and for a base of an inch square. 



Cast iron ; 18,400,000 lbs. Tredgold. 



White marble 2,520,000 



Elm 1,340,000 



Lead, cast 720,000 



Best double shear steel*, not hardened... 31,165,000 

 Bell metal f, same as in our experiments 11,380,000 

 Soft brass J, same as in our experiments 10,440,000 



Glass, from window-glass 8,580,000 



Ivory 1,630,000 



Cork 2,369 



Suppose it were required to find the elasticity of glass struck 

 against brass. 



The modulus of a glass being 8,580,000, and that of brass 

 10,M0,000, their relative hardness is as 86 to 105 nearly; and 

 the elasticity of glass is -94 and of brass -41 (Expts. 24, 22.) : 

 hence in the formula, for the elasticity above, we have a = 86, 

 a' = -94, h = 105, V = -41, 



. ah< + ba! _ 86 x '41 + 105 x -94 _ ^r. ,. , 



a + b 86 + 105 -^"^theeias- 



ticity required (being J^- th less than that given by Exp. 34.). 

 In impacts between other bodies we have as follows : 



Names ofBodies, with their Elasticities, ^^to. Elas^fcfties. Errors. 



Glass (-94) against lead (-20) -257 -25 ^ 



Glass (-94) against bell-metal (-67)... 82 -87 — -p>- 



Ivory (-81) against cork (-65) -64 -60 ji 



* A bar of best double shear steel, not hardened, -99 inch deep, -96 inch 

 broad, and 6 feet 8 inches long, weighing 22§ lbs. was laid on props 6 feet 

 asunder, and 196 lbs. suspended from the middle bent it -63 inch without in- 

 juring its elasticity: other weights, as 252, 308, 364, 420, bent it -81, 1-00, 

 1-17, 1*35. The experiment was made with great care, and a long wedge of 

 wood was employed to measure the deflections. 



t A bar 2 feet between the supports, -51 inch deep and 1-03 inch broad, bent 

 •27 inch with 121 J lbs. without injuring its elasticity : 304 lbs. bent it -62, and 

 318 broke it. 



X A bar 2 feet between the supports, -52 inch deep, and 1-04 inch broad 

 bent -15 inch by 66^ lbs. without injuring the elasticity: other weights, as 

 94^, 150i, 1711, 219i,bent it -22, -48, -70, 2-87, showing its great softness and 

 flexibility. Its modulus calculated for double the weight necessary to destroy 

 its elasticity was only 5,270,000 lbs., half that given above. 



The modulus for glass was obtained from the mean between three experi- 

 ments made by bendingslips of window-glass,giving 9,600,000lbs., 8,505,000lbs.. 

 and 7,634,000 lbs. 



The modulus for ivory was obtained by bending two slips of ivory ; and for 

 cork by compressing a rectangular piece 16 inches long and 2-05 inches sec- 

 tion ; the decrement with 127 J lbs, being -42 inch. 



