T>(S Messrs. K. Honda and T. Terada on the Chamje of 



(b) Measurement of the Coefficient of Elasticity. 

 Since it was necessary, in the calculation of ^ , to know 



the coefficient of elasticity in no field, a special arrangement 

 was devised for this purpose. 



Referring to fig. 2, m is the specimen, at the ends of which 

 brass rods of moderate diameter are brazed. The upper rod 



Fig. 2. 



M' 



M 



M 



d4*k] 



i 



M 



W 



is clamped to the tripod A resting on a rigid wooden frame. 

 To the lower rod is attached a flexible cord, which, passing 

 through the interspace between the grooves of two friction- 

 wheels P fixed to a stand, carries the scale-pan for the 

 weight W. Near the upper and lower ends the specimen 

 touches the horizontal axes, carrying two mirrors M and M' 

 respectively. The axes are so pivoted at their ends that they 

 rotate with almost no friction. S is a vertical glass scale 

 illuminated from behind; its image formed by successive 

 reflexions in M and M - ' is observed by a telescope T. If the 

 load on the pan causes the elongations SV and SI respectively 

 at M' and M. the rotations of the axes are given by 



<f>'= - and <f> = 



r 



where r is the common thickness of the two axes. 



if n and n be the deflexions of the scale due to separate 



rotations cj> f and <p respectively, we have 



Again, 



