2 Mr. C. Chree on the 



scarcely fitted to supply accurate numerical results, the in- 

 terest attaching to his observations is chiefly historical. 



A slight modification of Despretz's method was applied by 

 Herr Paalzow *, who sought to determine whether there was 

 any connexion between the conductivities for heat and for 

 electricity possessed by various liquids. He observed the 

 stationary temperatures finally indicated by four thermometers 

 at different depths below the surface of the liquids, where the 

 heat was applied. The formulae he employed do not seem 

 likely to give anything directly proportional to the conduc- 

 tivity, but his observations were sufficient to prove that no 

 relation exists between the conductivities for heat and for 

 electricity. For instance, water and sulphuric acid conducted 

 heat very similarly, the former being, according to Paalzow, 

 slightly the better conductor. 



In the article on Heat, in the Encyclopaedia Britannica, Sir 

 W. Thomson quotes with approval the value obtained by 

 Mr. J. T. Bottomley for the conductivity of water. The 

 method employed was a slight modification of Despretz's, hot 

 water being cautiously poured on the top of a board, of dia- 

 meter slightly less than that of a vertical wooden cylinder 

 containing water on which the board floated. The method 

 seems open to the same objections as Despretz's, and the com- 

 parison of other fluids with water would involve considerable 

 difficulties. Bottomley found for the absolute conductivity of 

 water in the C.G.S. system *002 ; but, as will be seen, this 

 differs somewhat widely from subsequent and more reliable 

 results. 



In the ' Philosophical Transactions ' for 1869, p. 637, is a 

 paper on our subject by the late Prof. Guthrie. As the 

 memoir is readily accessible, it is sufficient to say that his 

 apparatus consisted of two equal hollow metal cones, which 

 could be placed with their bases horizontal at small determi- 

 nate distances apart. The liquid to be examined was intro- 

 duced between the bases, where it was maintained by the 

 capillary forces at its surface. A current of hot water was 

 circulated through the upper cone, and the temperature of the 

 air in the lower cone was determined by the height of a column 

 of coloured fluid in a tube communicating with the interior 

 of the cone. 



The deductions made by Prof. Guthrie from his experi- 

 ments are of an extremely fallacious nature, and as they are 

 not infrequently quoted it seems desirable to examine them 

 briefly. 



In his first series of experiments a hot current was suddenly 

 * Pogg. Ann. cxxxiv. 18G8, p. 618. 



