carried by the Ions produced by Rontgen Rays. 539 



sation begins, and p the density at the temperature t ; hence 

 we have CM 



P = Pi- -£-(t-t 2 ). 



Since p is a function of t, this equation enables us to 

 determine t. If x is the ratio of the final to the initial volume 

 and t the temperature before expansion, then, since the mass 

 of unit volume of air is '00129 grm. at 0° 0. and under a 

 pressure of 760 mm. of mercury, we have 



,, -00129 273 

 M= x 



273 + *</ 



if we take the initial pressure to be 760. 

 Again, 



Pl ~x } 



where p is the density of water-vapour at the temperature t . 

 The cooling caused by the expansion is determined by the 

 equation 07Q , , 



C=-167; L = 606. 



THUS -^o_^I -00129 273 



P ~ x 606 X x 2T6 + t {t ~ t2) - 



Let us apply these equations to a special case. In one of 

 the experiments £ =16° C. and 



™>-13-5 =1 . 36; 



760-13-5-197 



, 273 + 16 , tl t _ 

 l0 ^ -273 + ^7 =' 411o « 1 ' 36 

 =Iog 1*134; 

 hence 273 + * s = 254*8, 



f2 =-18-2, 

 Po = -0000134, 



.-36 

 *273 



98-4 xlO- 7 , 



hence 



606x1-36x289 -**°* 1U ' 



/d = 98-4 x 10- 7 - 2-46 x 10~ 7 ( t + 18-2). 



