﻿394 Royal Society : — 



is required in order completely to reduce the temperature of half 

 a gramme of water from 100° to 0°. This source of error, which 

 has been the chief cause of the dismissal of Laplace's calorimeter 

 from among the ranks of exact physical instruments, and which 

 is in no way diminished in Herschel's improved form, is entirely 

 removed by the principle which I adopt. According to my me- 

 thod, the bodies whose loss of heat is to be measured by the 

 contraction of the melting of the ice are contained in a vessel 

 perfectly impenetrable for heat ; whilst at the same time any error 

 from transference of heat to the air is avoided, as the bodies are 

 placed in a mass of water at C C, so that the warmed water, 

 the temperature of which never rises above 4° C, always flows 

 to the lowest part of the vessel. 

 Heidelberg, April 14, 1871. 



LIII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 318.] 



Feb. 2, 1871.— General Sir Edward Sabine, K.C.B., President, in 



the Chair. 

 HTHE following communication was read : — 

 ■*■ " On the Uniform Flow of a Liquid." By Henry Moseley, 

 M.A., D.C.L., Canon of Bristol, F.R.S. 



The resistance of every molecule of a liquid at rest which a solid 

 (by moving through it) disturbs, contributes its share to the resist- 

 ance which the solid experiences ; so that the inertia of each molecule 

 so disturbed and its shear must be taken into account in the aggre- 

 gate which represents the resistance the liquid offers to the motion 

 of the solid. The motions communicated to the molecules of a 

 liquid by a solid passing through it, and the resistances opposed to 

 them, however, are so various, and so difficult to be represented ma- 

 thematically, that in the present state of our knowledge of hydrody- 

 namics the problem of the resistance of a liquid at rest to a solid 

 in motion is perhaps to be considered insoluble. As it regards the 

 opposite problem of the resistance of a solid at rest to a liquid in 

 motion (as in the case of a liquid conveyed through a pipe), there 

 are in like manner to be taken into account the disturbances created 

 by that resistance in what would otherwise have been the motion of 

 each individual molecule of the liquid so disturbed. 



This problem, however, is by no means so difficult as the other. 

 There is, indeed, a case in which it admits of solution. It is that 

 of a liquid flowing from a reservoir, in which its surface is kept 

 always at the same level, through a circular pipe which is perfectly 

 straight, and of the same diameter throughout, and of a uniform 

 smoothness or roughness of internal surface, and always full of the 

 liquid. The liquid would obviously in such a pipe arrange itself in 

 infinitely thin cylindrical films coaxial with the pipe, all the molecules 

 in the same film moving with the same velocity, but the molecules 



