182 Mr. T. H. Blakesley on some Facts connected with 



acceleration, energy, and E.M.F., 900 ; and power, 27,000 

 times of the practical units ; while capacity sinks to -q\-q of a 

 farad. 



This would, however, leave the connexion between the unit 

 of power and 1 horse-power bad, for 1 unit would be about 

 36-2 H.R 



The correlation of temperature with other units would be, 

 I imagine, best effected by the definition that a unit-of- 

 teraperature change shall be that through which a unit of 

 energy in the form of heat would raise a unit of matter pos- 

 sessing unit specific heat ; in other words, the equation 



'niPt~'^=^3'mc6 

 should be satisfied by J = l. 



Since heat is recognized as energy, J must be numerical, 

 notwithstanding arguments have been adduced against this 

 view. It is sometimes said that J cannot be numerical 

 because it changes with a change of units. This only arises 

 from the fact that heat in the form mcd is not properly corre- 

 lated, because (c6) is not so. Those who use this argument 

 should apply it in some other case, when the fallacy would be 

 apparent ; e. g. 



Power in watts = 746 horse-powers, 



Power in ergs per sec. = 10^ x 746 horse-powers. 

 Here the factor has changed with a change of units, but no 

 one would deny its being numerical, or the relation of one 

 magnitude to another of the same nature. 



If therefore J is reduced to unity by the above definition, 

 we have (c9) = Pt~^ for the dimensions of temperature x 

 specific heat ; and if c is taken as numerical, these become the 

 dimensions of 0. 



As regards the relation between a degree so obtained and a 

 thermometer-degree, we have the following facts to go upon: — 

 4'2 X 10^ ergs raise 1 gram of water 1° C, 



.*. 1 erg raises 1 gram of water through ( j;^^ — r-^) C. 



.-. 1° C. = 4-2 X 10^ degrees C.G.S. (water). 

 1°F. = 2-3x10^ „ „ „ 



1°R. = 5-25x10^ „ „ 

 These degrees therefore do not fit in decimally with the 

 arbitrary scales in use. 



But the number 4*2 may be written ,., ,. . If therefore 

 •^ •23«1 



we use as the standard of specific heat a substance which, 



