Stress and Strain on the Properties of Matter. 107 



Table IV. 



Metal. 



Condition. 



Modulus of 



torsional 

 elasticity in 

 grams per 

 square centi- 

 metre obtained 

 by the statical 

 metbod. 

 *■«« 



Ditto obtained 

 by the kinetical 

 method. 



ft 





Annealed 



751-5 xlO r> 



766-5 xl0 6 



1-020 



Platinum . . . 



TJnannealed 



662-2 



663 -5 



1-002 







275 5 



278-0 



1-009 



Aluminium . . 



» 



267 7 



266-9 



0-997 



The values of rk given in Table IV were obtained from the 

 formula — 



_ 2LM7T* 



n ~ 981-4*V 2 ' 



where L is the length of the wire, t the time of vibration, s the 

 section, M the moment of inertia, and 981 '4 is the value of g at the 

 place, the units being throughout C.G.S. 



It will be seen that for the hard-drawn metals the values of r s and 

 rk agree with each other within the limits of errors of observation, and 

 that for these metals the mean value of r s jrk is ]*0043. It is impos- 

 sible in this case to make an exact comparison of the values of r s and 

 rk, when for the former allowance is made for the effects of loss and 

 gain of heat, since the times of vibration in the kinetical method 

 were too long* to avoid gain and loss of heat in using the method, 

 but if the correction could be accurately applied, it would evidently 

 on the whole bring stili greater accordance between the values of sri 

 and r s . 



For the annealed iron the value of r s exceeds that of n by an 

 amount which is greater than can be attributed either to heating and 

 cooling effects or to errors of observation. 



Summary. 



1. The value of the modulus of longitudinal elasticity for hard- 

 drawn metals, as determined by the statical method of loading, accords 

 with the value obtained by the method of longitudinal vibrations, pro- 

 vided the deformations produced in using the former method are suffi- 

 ciently small. 



* The times of vibration varied from 6 to 9 seconds. 



