THE LAWS OF ELASTICO-VISCOUS FLOW. 11^ 



A. A. MICHELSON 



University of Chicago 



In a paper of Harold Jeffreys entitled "The Viscosity of the 

 Earth "^ the author makes use of a formula which combines the 

 laws of Larmor and of Maxwell. 



The integral implies a permanent set which, as the author indicates, 

 would be inconsistent with the "accepted theories of tidal friction 

 and variation of latitude. Hence ti must be practically infinite." 



ds 

 The formula is thus reduced to the expression F^n^ 5+r2-^. 



Experiments made on a great variety of materials show, how- 

 ever, that this expression must be seriously modified to represent 

 the facts. 



Thus it has been shown^ that the displacement produced by a 

 stress P is given by the expression S = C,Pe^'^ -^-C^Pe'^^ii -e-'^V't) + 

 C^PeH''.'^ The last term produces permanent set, so that for the 



I II- 



present it may be omitted. Putting Ci = — and C2 = — ,a = -,0 = 1/ / , 



this becomes 



S^P\. .n.A. 





whence 



' "The Laws of Elastico- Viscous Flow. I" appeared in Jour. Geol., XXV (1917), 

 pp. 405-10- 



^ Monthly Notices of the Royal Astronomical Society, LXXVII, No. 5. 



3 "The Laws of Elastico-Viscous Flow," Jour. Geol., XXV (191 7). 



1 The strains in these experiments were torsional, thus involving only the rigidity 

 constant n. In the formula as given in the paper referred to the coefficients C and the 

 exponents h are functions of the temperature. The stress P is constant and p is 

 approximately one-half. 



