890 



A Determination of Poissons Ratio. 



method, and the longitudinal and transverse deflexions were 

 of the same order of magnitude. 



The lengths a and b were measured with a travelling 

 microscope. 



The results o£ experiments made by the second method are 

 given in the following table. 



Results. 







Deflexion 



Scale 















per kgrm. 



Distance. 







Distance 



of Load 



from 















L 



->ad. Long. 



Trans. 



Long. 



Trans. 



a 



b 



Knife- 



R 



Expt. 



kg 



rms. Scale. 



Scale. 



S. 



S x . 



cm. 



cm. 



edge. 



ff -E L . 







mm. 



mm. 



cm. 



cm. 







cm. 





1 







-3 972 



11-87 



68-1 



1264 



1970 



1-087 



200 



•2924 



o 





1210 



14-82 











25-0 



•2932 



3 





14-75 



17-97 



68-0 



126-4 



19-78 



1-090 



30 



•2909 



4 





14-75 



18-10 











30-0 



•2930 



5 





11-75 



11-85 



82-2 



126-4 







200 



•2910 



6 





11-70 



11-85 











20-0 



•2923 i 



7 





14-67 



14-87 









... 



25-0 



•2925 



8 





14-67 



14-87 









... 



25-0 



•2925 



L = 401 cm. B = 2-49 cm. 

 Mean Value of a = '292. 



The bulk modulus k of an isotropic solid may be calcu- 

 lated from either of the two well-known equations 



where 



k = 



E 



3(3ai-E)' 

 E 



3(1 -2er)' 

 E = Young's Modulus, 

 n = coefficient of rigidity, 

 a — Poisson's Ratio. 



An accurate knowledge of a would enable us to calculate 

 k from each of the above equations and determine from the 

 degree of agreement in the results how far we were justified 

 in using either of the equations to determine k. 



