86 



actly of the bigness of the originals. If any of them are new to you, and 

 are worth your notice, it will give me much pleasure. . . yr^ &c., 



(Signed) James Simon-. 



' P. S. — IsTo. 1 was found in the lands of Mr. James Commins, about 

 4 foot deep, in making a ditch near a place called Key's hole, in the west 

 part of the county of Clare. 



'"I have drawn these, that the Society may have a conception of 

 them, over leafe.' " 



The Eev. Samuel Hatjghton read the following paper : — 



On the DrNAMiCAL Coefficients of Elasticity of Steel, Ieon-, Beass, 



Oak, and Teak. 



All works on mechanics, with which I am acquainted, in solving the 

 problem of the collision of bodies, assume that the momentum is pre- 

 served during the shock, and the vis viva lost, in such manner as to re- 

 tain the constancy of the Coefficient of Elasticity, which is defined to be 

 the ratio which the velocity of separation of two bodies after the shock 

 bears to the velocity of approach before the shock. Some time ago, in 

 making some calculations respecting armour-plated frigates, I found it 

 necessary to use the Dynamical Coefficients of Elasticity of steel, iron, 

 oak, and other substances, and made some experiments for the purpose 

 of determining them. These experiments were made at the Kingstown 

 Eailway works, and consisted in dropping spherical balls (2^ in. diam.) 

 of steel, iron, and brass upon levelled surfaces of steel, iron, oak, teak, 

 &c., and measuring the height of the rebound. I hope at some future 

 time to lay the results of these experiments in detail before the Academy ; 

 but at present I shall content myself with publishing the following Table, 

 which contains the means of many experiments. 



Erom this Table the remarkable fact appears, that the Dynamical 

 Coefficient of Elasticity is not constant, but diminishes, according to some 

 unknown law, as the velocity of the collision increases. 



