1894.J Water as determined by the Microrheometer. 



261 



and 4 contain the calculated values for the first and second parts of 

 the formula respectively, and in Column 5 are the values for the 

 viscosity obtained by subtracting the figures in Column 4 from those 

 corresponding to them in Column 3. 



On comparing these results with the values given by Poiseuille, 

 Slotte, Sprung, and Thorpe and Rodger as tabulated below (IT), it 

 will be seen that Mr. Hannay's observations yield discordant, and, 

 indeed, utterly absurd, values for the viscosity of water. At 0, for 

 example, the viscosity would appear to be below that of any known 

 liquid, and at 6 it becomes nil. 



Table II. Water. 

 Viscosity Coefficients in Dynes per sq. cm. between and 100. 



As a matter of fact, it is physically impossible to pass a volume of 

 water such as Mr. Hannay employs under a pressure of 1 m. of 

 water through a capillary of the dimensions given in the time re- 

 corded. At 20, for instance, the time of flow required under these 

 conditions would be about 4600 seconds instead of 131 '3 seconds as 

 stated. 



I have carefully examined Mr. Hannay's data with the object of 

 discovering any slip or misprint which might satisfactorily account 

 for the discrepancy. Thus, I have tried the effect of substituting 

 "centimetre" for "millimetre," and "radius" for "diameter" in 

 the dimensions given, but no alteration of the kind could be made to 

 yield values for 17 agreeing with those of other observers. 



In the light of these results, it would seem to be premature to 

 discuss Mr. Hannay's observations on saline solutions, or to criticise 

 the generalisations he deduces from them. 



