Lieut.-Col. A. R. Clarke on the Elasticity of Brass. 131 



mical combustion of the iron and troilite contained in the me- 

 teorite. The last point has been already considered ; on the 

 other I have only to observe that, were the hollowing-out of a 

 meteorite due to such little whirlwinds on its surface, we should 

 find traces of the rotatory action in a whorl-like distribution or 

 marking of the crust. We do not find this, whereas we do 

 find very often distinctly marked traces of the orientation of 

 the meteorite at a given period in its course, indicated by 

 the backward flow of the then molten crust, which, like some 

 old lava stream in petto, still presents lines following the course 

 of that flow on the surface, and a denser incrustation in the 

 rear than on the front, from which the backward-streaming 

 lines take their course. 



The subject here discussed, however, is bound up with ques- 

 tions as to the original form in which meteorites enter our 

 atmosphere, questions that have recently been discussed from 

 two very opposite points of view by F. Mohr in Liebig's An- 

 nalen (vol. clxxix. pp. 257-282), and by Professor Tschermak, 

 in the June Supplementary Number of the Philosophical Maga- 

 zine for this year. I will take a nearly opportunity of asking 

 you to record my views on both of them. 

 I am, yours &c, 



N. Story Maskelyne. 

 112 Gloucester Terrace, W., 

 July 17, 1876. 



XVIII. On the Elasticity of Brass. 

 By Lieut.-Col. A. R. Clarke, C.B., R.E., F.R.S., $e* 



IN the course of a recent measurement of the distance be- 

 tween the knife-edges of Kater's Pendulum, it became 

 necessary to consider the question of the change of length 

 which takes place when the position of the pendulum is changed 

 from vertical to horizontal, and also the alteration in length 

 caused by interchanging the knife-edges in swinging. The 

 values of the modulus of elasticity which are found in the ordi- 

 nary books of reference are given, so far as I have seen, with- 

 out any statement of the authority on which they rest ; and it 

 does not appear that any precise experiments have been made 

 in this country on the elasticity of brass, though those of iron 

 and steel are well determined. Some circumstances having 

 led me to doubt the accuracy of the value taken from the Table. 

 a simple experiment on the flexure of a brass scale was made, 

 which gave a very different value. 



In order to get some precise results, I obtained four speci- 



* Communicated by the Author. 

 K2 



