186 THERMODYNAMIC ANALOGIES. 



is, a number taken from a table of numbers proportional to 

 the weights of various molecules and atoms, but having one 

 of the values, perhaps the atomic weight of hydrogen, arbi- 

 trarily made unity, the law of Boyle, Charles, and Avogadro 

 may be written in the more practical form 



pv = A'T-^, (497) 



JXL 



where A' is a constant and m the weight of gas considered. 

 It is evident that 1 K is equal to the product of the constant 

 of the law in this form and the (true) weight of an atom of 

 hydrogen, or such other atom or molecule as may be given 

 the value unity in the table of molecular weights. 



In the following chapter we shall consider the necessary 

 modifications in the theory of equilibrium, when the quantity 

 of matter contained in a system is to be regarded as variable, 

 or, if the system contains more than one kind of matter, 

 when the quantities of the several kinds of matter in the 

 system are to be regarded as independently variable. This 

 will give us yet another set of variables in the statistical 

 equation, corresponding to those of the amplified form of 

 the thennodynamic equation. 



