1894.] Specific Heat of Water in Electric Units. 31 



We now turn to an investigation of Miculescu ('Annales de Chimie 

 et de Physique,' vol. 27, 1892), in which the mechanical equivalent 

 of heat is measured directly by what seems a very excellently 

 devised series of experiments. Its result is 4'1857 X 10 7 . He does 

 not state the exact temperature to which this applies, but all his 

 experiments seem to have been made between 10 and 13, so 

 that we may assume 11'5 to be the mean temperature of his experi- 

 ments. Rowland's value at that temperature is 41999 X 10 7 . We 

 must draw attention to one point in Miculescu's work which requires 

 clearing up before we can give to it any decisive value. Everything 

 in the experiments depends on the measurement of a couple, the arm 

 of the couple being the distance between two knife-edges ; one of 

 them had to support a weight of more than 43 kilograms. The dis- 

 tance between these knife-edges is said to have been 28 cms. in all 

 experiments. Very insufficient information is given, however, as to 

 how that distance was measured, and it would almost seem as if the 

 author had trusted to the maker in adjusting the central knife-edge 

 to the zero point of that scale. If the apparatus is still in existence> 

 it might be well to make sure that no error has been introduced 

 through a wrong estimate of the distance of the lever arm. 



In order to compare Miculescu's value with that of others, we must 

 apply a temperature correction which is somewhat doubtful ; but 

 taking the mean of Rowland's and Griffiths' values as the most pro- 

 bable at present, we obtain at 15 the following table: 



Table IV. Equivalent in foot-pounds at Greenwich at 15 

 referred to the " Paris " Nitrogen Thermometer. 



Schuster and 

 Joule. Kowland. Miculescu. Griffiths. Gannon. 



775 778-3 776-6 780-2 779'7 



If we remember that Rowland's nnmber referred to the " Paris " 

 nitrogen thermometer would probably be smaller by one unit, we 

 are strnck with the fair agreement there is, on the one hand, between 

 the results of Joule, Rowland, and Miculescu, and on the other hand 

 between Griffiths and ourselves. 



As far as, we can draw any conclusions from the comparison, it 

 seems to point to a difference in the value obtained by the electrical 

 and direct methods. Whether this difference is due to some remain- 

 ing error in the electrical units, or to some undiscovered flaw in the 

 method adopted by Mr. Griffiths and ourselves, remains to be 

 decided by farther investigation. 



