Nipher — The Law of Contraction oj Gaseous Nebulae. 151 



and every unit mass has been multiplied by m"^. Each unit 

 mass may be supposed to lie as a piston in a fixed radial cone. 



After the piston descends, its area becomes — , of its initial 



value. The force per unit area, due to the weight of super- 

 posed layers, becomes wi* times as great, or 



P = m* P^- 



The product Pv has therefore become m times as great 

 as it was in the initial stage. Therefore by the equation 

 Pv=CT 



Eliminating m in these equations Ritter obtained equations 

 corresponding exactly to (23) (24) and (25), viz.: 



Pv^ = P^ vj ; Tv^ = T^v:' and — — ^ " 



0^0 



p~ p. 



but he did not determine the values of these constants, 

 as is done in (26). Ritter saw very clearly, however, 

 that these three equations were characteristic of a gravi- 

 tating mass in equilibrium under its own forces, as dis- 

 tinguished from the case where a few grammes of gas 

 are held in the cylinder of a heat engine. In the latter 

 case the gas may be compressed and cooled or heated 

 in any way that can be imagined. The value of n 

 in eq. (3) may be anything between + co and — oo , and the 

 range in specific heat will be as wide as that of n, as is shown 

 in the table at the beginning of this paper. He concluded 

 that his equations, last given, were the projections on the 

 three reference planes, of the path on the surface represented 

 by eq. (1), traced by a point representing the changing con- 

 dition of any unit mass in his gravitating gaskugel. Ritter 



therefore concludes that the value of >i in eq. (3) is r and 



3 



