﻿[ 468 ] 

 LXV. Proceedings of Learned Societies, 



ROYAL SOCIETY. 

 [Continued from p. 394.] 



Jan 21, 1869. — John Peter Gassiot, Esq., Vice-President, in the 



Chair. 

 rj^HE following communication was read : — 

 A "On the Thermal Resistance of Liquids." By Frederick 

 Guthrie. 



The memoir of which the following is an abstract gives an account 

 of some experiments made by the author with the object of deter- 

 mining the laws according to which heat travels by conduction 

 through liquids. 



After pointing out the importance of the subject, and briefly re- 

 capitulating the methods previously used and the results obtained 

 by other experimenters, the " Diathermometer " is described. 



This instrument, which may be employed for the examination 

 of the thermal resistance or conducting power of solids as well as 

 liquids, has the following form. A hollow brass cone, having a pla- 

 tinum base, is screwed with its apex downwards into a tripod stand 

 which rests upon adjusting screws. The apex of the cone is tu- 

 bular, and carries a cork, through which passes a vertical glass 

 tube graduated and dipping into water. The level of the water in 

 the tube is nearly as high as the apex of the cone. By means of 

 a micrometer screw, a second cone, exactly similar and equal to 

 the first, having its apex upwards, may be brought to any required 

 distance from the lower cone. The brass cones and their platinum 

 faces are highly polished, and the latter are cleaned by washing 

 successively with hot nitric acid, caustic soda, alcohol, and water. 

 The upper surface of the lower cone is brought into an exactly hori- 

 zontal position, and the upper cone is lowered to any required dis- 

 tance from it. There is thus formed between the platinum faces 

 a cylindrical interval of known height or thickness, and diameter, 

 and having its opposite faces parallel and horizontal. This wall-less 

 chamber receives the liquid whose thermal resistance has to be mea- 

 sured. A liquid, introduced by means of a strangulated pipette of 

 known capacity (equal, say, to the interstitial space when the cone- 

 faces are 1 millim. apart) between the cones, remains there by means 

 of its adhesion and cohesion. A description is given of the method 

 used to get a constant current of water of uniform and known tem- 

 perature to pass through the upper cone. When such a current 

 passes, the platinum face of the upper cone becomes heated ; it 

 communicates its heat to the liquid in contact with it. The heat 

 passes downwards through the liquid, heats the upper surface of the 

 lower cone, expands the air therein, and depresses the level of the 

 water in the tube attached to the lower cone. 



A description is given of the most prominent sources of error of 

 this instrument, and the means which were employed to eliminate 

 them. It is concluded, from direct experiments (1st by measuring 



