106 Prof. A. W. Riicker on the Suppressed 



whicli is the absolute temperature generally accepted as equi- 

 valent to 0° 0. Heat absorbed by a gas at constant volume 

 would be at once expressed in dynamical measure by the 

 product of the change in temperature and of two abstract 

 numbers, viz. the ratio of the number of molecules to the 

 standard number, and the ratio of the increase of the total 

 energy of a molecule to that of the energy of translation. 

 Even if some such system should ultimately be adopted, our 

 knowledge of the molecular construction and dynamics of 

 solids and liquids is as yet too imperfect to warrant an attempt 

 to place thermal units on a natural and mechanical basis. 

 Until such a reform can be carried out, I think it would be 

 best to place temperature in a class of secondare/ fundamental 

 units, which, owing either to our ignorance or to our artificial 

 methods of measurement, cannot be expressed in terms of 

 length, mass, and time, and which must therefore be regarded 

 as fundamental to other derived units which depend upon 

 them. 



The thermal units could then be tabulated in a more syste- 

 matic manner than is usual, and the arbitrary character of the 

 system would be emphasized by the symbol employed to 

 represent the dimensions of temperature. If 6 be the symbol 

 chosen, if specific heat be taken as a number, and the unit of 

 heat be defined with reference to the unit mass of water, the 

 following results are obtained : — 



Quantity of heat [M6'] 



Mechanical equivalent of heat . . . [L^ T"^ ^~^] 



Specific heat 1 



Latent heat [^] 



Thermal capacity [M] 



Coefficients of expansion [^"^] 



Coefficients of abso.poion and emission [ML~^ T"-^] 



Coefficient of conductivity .... [ML-' T-i] 



Entropy [M] 



Gravitation units hardly come within the scope of the 

 present naper, but as they are important in their applications 

 to thermal quantities I may indicate a method of dealing with 

 them. 



We must distinguish between the nominal unit of mass in 

 such a system (M) and the real unit (M7), where 7 is the 

 abstract number which expresses the acceleration of gravity 

 in terms of the units of length and time. The three funda- 

 mental units in such a system are length, time, and force. 

 Mass is a derived unit subject to the condition that [L T"^] 



