THE LAWS OF ELAST I CO-VISCOUS FLOW 21 



Table I shows the very great increase in importance of the 

 elastico-viscous term for large stresses. The same is also true for 

 the purely viscous term. 



TABLE I 



P = S/P 



o I 



1 1.2 



10 7 . 



50 20,000 . 



Table II gives the ratio — for twenty-two materials, showing 



that there are certainly two elasticities, one of which is not accom- 

 panied by viscosity and the second is thus affected. In every 

 case excepting that of sealing wax, where the ratio is unity, the 

 second elasticity is much greater than the first, and in some cases 

 enormously greater. 



TABLE II 



fll 111 



Tin 60 Slate 150 



Zinc 70 Shale 50 



Marble 45 Soapstone 35 



Limestone 30 Lead 40 



Ebonite 8 Cadmium 65 



Iron 2,200 Gold 150 



Steel 12,000 Magnesium 250 



Copper 8 Bapelite 7 



Aluminum 4,400 Ivory 50 



Talc 200 Silver 80 



Glass 100 Sealing wax i 



The introduction oi \/t instead of t itself is a step so radical 

 that it may be well to give an illustration in its justification. For 

 this purpose it is desirable to choose a material in which the elastico- 

 viscous effect is well marked. This is notably the case for vul- 

 canite, which has the added advantage of the relatively small 

 importance of the third or purely viscous term. This illustration 

 is perhaps the most striking in showing the appropriateness of Vt 

 instead of t; but all the materials investigated give similar results. 



