for determining the viscosity of very viscous liquids 29 



If the value of h^ corresponding to M^ is read off from the 

 curve of Diagram 2, the viscosity 17 can be calculated by equa- 

 tion (3). The values of k found from Diagram 2 have been used 

 in forming Table 3. 



Table 3. 



Values of M^T/il + k^). 



From Table 3 it appears that the area in Diagram 1 in which 

 equation (3) holds good is restricted to that part of the diagram 

 to which the parabolic boundary curve is convex. From the values 

 of MT derived from Table 1 and plotted in Diagram 1, the equation 

 of the parabola is found to be M'^ = 11-26 {MT). I have not been 

 able to give the parabola any definite physical interpretation, and 

 it ought to be regarded as representing a diffuse limit region. But 

 it is only when we pay regard to this, that we obtain values of 7) 

 differing from each other by amounts lying within the limits of 

 experimental error*. To make a comparison with the values of 

 M and I which Dr Searle has used, I have, in Diagram 1, plotted 

 (the broken hne) his values of i/Tf (strictly speaking, MTjC, 

 which are comparable in magnitude with my values of MT) 

 against M. 



Dr Searle has pointed out to me that the effect shown in 

 Diagram 1 might conceivably be due to pivot friction. I have 

 carefully considered this possibility. Before the liquid was put 

 into the apparatus, I adjusted the pivots so that the rotation due 



* Compare G. F. C. Searle, loc. cit., Table II, p. 606. 



I Calculated from Table 1, G. F. C. Searle, loc. cit., p. 605. 



