Conduction of Heat in Liquids. 13 



while Weber has 



<f = 4-778. 



Lorberg's work, with the arithmetical coefficients of which I 

 do not entirely agree, would indicate that the term in h, itself 

 supposed to be a very small quantity, is negligible without 

 sensible error. Thus, Lorberg's more exact treatment would 

 alter Weber's values for the conductivity by less than \ per 

 cent., which is far less than the probable experimental error. 

 In my opinion Lorberg, in not a few cases, uses more figures 

 after his decimal point than circumstances warrant. He is 

 also entirely dependent on Weber's measurements of the 

 apparatus, which are hardly likely to possess the extreme 

 accuracy he supposes. It would, for instance, be difficult to 

 determine the distance between the copper plates exact to 

 one-hundredth of a millimetre ; but an error of this amount 

 would produce as great an effect in the value of the con- 

 ductivity as Lorberg's corrections do. 



I shall now examine somewhat closely Weber's and Lor- 

 berg's numerical deductions from the former's experiments. 

 When dealing with water at a low temperature, Weber took 

 observations every ten seconds. He denotes by x n the 

 (n+l)th galvanometer-reading; thus x n and x n+ e denote 

 readings at an interval of one minute. A fall of 1° in the 

 hot junction corresponds to a decrease of about 17 divisions 

 in the galvanometer-reading. The Table on p. 14 is part 

 of a table given by Weber*, along with an extension by 

 Lorberg f. 



The first reading corresponds to a temperature 15°*59 in 

 the hot junction, and the last to 3°'56. 



The application of this table follows very simply from the 

 formula „. 



u = Ae~^\ 



Thus, assuming u a #, and counting t in minutes, we get 

 M/* 2 =log 10 — and also =log 10 * n ~*» +6 , 



where M = log 10 e= '43429 .... 



If, then, the mathematical theory were in all respects satis- 

 factory, the mean values in the third and fourth columns 

 should agree. The fourth column is due to Lorberg, and did 

 not come under Weber's attention. The latter, however, 

 points out that in the third column there is, on the whole, a 



* Wied. Ann. x. p. 308. f Wied. Ann. xiv. p. 442. 



