Conduction of Heat in Liquids. 



47 



chance. In the case of water, there is a decided though not very 

 serions discrepancy. The difference in the mean temperature of the 

 two experiments could account for only a small part of this. v The 

 experiments on water were the earliest in which the siphon was used, 

 and the operation took slightly longer and its results were not quite 

 so uniform as in later experiments. Farther, when no siphoning 

 took place, the heat passing into the liquid at the end of the expe- 

 riment was much larger in the case of water than for the other 

 liquids, and the terms at the limits in (5) would thus be of slightly 

 greater importance for water than for the others. Also an error of 

 given amount in the experimental determination of the time of most 

 rapid heating would produce the greater effect the shorter the time, 

 and would thus modify the results for water more than for any other 

 of the liquids, except bisulphide of carbon. Thus it was only to be 

 expected that the greatest discrepancy between the results of the 

 two methods should occur in water. 



With the larger apparatus results were obtained for water and 

 methylated spirit, of the same constitution as in the experiments 

 already described, which, though not pretending to great accuracy, 

 may be of interest as independent evidence of the correctness in the 

 main of the theory. For the intervals in minutes that elapsed after 

 the application of the heat before the temperature of the wire was 

 rising fastest, the mean of several experiments gave 52J for water, 67-J 

 for the spirit. The water was left undisturbed in the dish, and no 

 accurate observations of the rate of cooling were made. It was noticed, 

 however, that the dish parted rapidly with its heat, and being only 

 slightly deeper than the dish in the small apparatus, it is pretty clear 

 that by far the greater part of the heat was given to the liquid in the 

 tub in the first few minutes. Thus the experiment would be pretty 

 much akin to the case when the water was siphoned in the smaller 

 apparatus. Though ignorant of the law of cooling, we can thus obtain 

 an inferior limit to the conductivity, of a moderately close kind, by 

 supposing the heat to have been instantaneously commuuicated. This 

 gives from expression (3), viz., h — 0'0917x 2 pc/t, for water k = 0*0730, 

 and for methylated spirit h = 0*0324, corresponding to temperatures 

 of about 18° C. These results as being essentially inferior limits, 

 agree fairly with those of the smaller apparatus. 



On the whole, the results of this series of experiments resemble 

 those obtained by Herr Weber.* The values obtained for the con- 

 ductivity of water agree fairly well with his. The smaller value 

 obtained by Weber for bisulphide of carbon, viz., 0*0250, would be 

 partly accounted for by the very considerably lower temperature of 

 his experiment. As this liquid boils at a very low temperature, the 



* ' Wiedemann, Annalen,' vol. 10, pp. 103, 304, 472 ; see specially table on 

 p. 314. 



