24 A. A. MICHELSON 



The expression for the viscous term should be S^, = {Ft)^ if the 

 stress (P) is constant. If P is a function of time 



S, = {lFdt)^. 



Thus if P be given a constant value for a time ^o and then 

 changed to Pj the corresponding value of the viscous term would be 



S, = {F,io-F,tf . 



If the first stress be considerable and act for a long time the 

 effect of the second stress is negHgible. 



Table IV is a provisional table of the constants which appear 

 in the formula for the torsional strain at room temperature. 



in which A=CPe''^. P is the weight acting on a pulley of radius 

 5 cm., the unit of weight being loo gms. and the unit of time one 

 minute. The specimen is a cyhndrical rod 7 . 5 cm. long and 4 mm. 

 in diameter. 



The term A^, which may be termed the "lost motion," should 

 probably be considered as a part of the viscous term, but with a 

 very small exponent r, so that the whole viscous term may be 

 represented by 



