;iso 



Mr. A. Mallock. Some Measure* of [Mar. HI. 





IV. " Some Measures of Young's Modulus for Crystals, &c." 

 By A. MALLOCK. Communicated by LORD RAYLEIGH, Sec. 

 R.S. Received March 9, 1891. 



The Table at the end of this communication contains the results of 

 experiments made in October, 1889 February, 1890, on the elasticity 

 of various bodies. 



The measures relating to crystalline bodies are, I believe, new. 



The method used to obtain these results was applicable to very 

 small specimens. This was a necessary condition in the case of most 

 crystals, because of the difficulty of getting large specimens without 

 flaws. 



In the experiments now to be described, I am dealing only with 

 the values of Young's modulus, but by a modification of the apparatus, 

 measures can be made of the simple rigidity, which will, I hope, 

 the subject of a future communication. 



Of course, the simple rigidity must lie between one-half and o: 

 third of the value of Young's modulus, according to the ratio be 

 longitudinal extension and lateral contraction (Poisson's con 

 for the substance. 



The apparatus used in my experiments is shown in figs. 1 and 2. 



Fig. 1 shows the general arrangement of the parts, and fig. 2 is 

 full-sized diagram of the mirrors and knife-edges. 



The lettering is the same in both figures. A, is a vertical 



FIG. 1. 



