/or determining the viscosity of very viscous liquids 31 



When the values of loge (-7 — 274-7) were plotted against O, the 

 curve was roughly a straight line. Hence x may be taken as unity, 

 and thus the number of constants to be found is reduced to two. 

 By the method of least squares, I obtained logf<^ = 4-375 and 

 A = 5-694, and thus 



r^ig.g = 274-7 + 79-44 e-^-''^'*". 



.(5) 



Equation (5) expresses the results of the observations when 

 Q. exceeds 0-1, but not for smaller values of Q. 



§ 6. Experiments carried out at different temperatures showed 

 that the curves representing the function 



T [MT, M\ 







are of the same character as those given in Diagram 1. Table 4 

 gives the values of 7] found for various temperatures. In these 

 experiments I was 10-0 cm. ; and, at each temperature, six different 

 loads were used, in order that I might be able to decide with 

 certainty that the values of M, used in calculating the value of 17 

 for each temperature, lay in the area to the right of the parabolic 

 boundary line of Diagram 1. The same value of k, viz. the limiting 

 value 0-48 cm. shown in Diagram 2, was used in calculating the 



Table 4. 

 Values of 7] at various temperatures. 



various values of rj. These values are not claimed to be exact. 

 In these experiments it was very difficult to keep the temperature 

 constant during each series of observations, and thus a deter- 

 mination of k for each temperature was out of the question. From 

 the curve of the function -q =f{t), shown in Diagram 4, it follows 

 that I drj/dt I rises rapidly as -q increases; this tallies with what 

 was said above. 



