On the Continuity of Isothermal Transformation. 231 



It will be found that these results together with equation 

 (18) give the actual medium described above. 



It is possible that a torsion other than the simplest (from a 

 strain point of view) would give simpler electromagnetic 

 results. The above torsion is the only one I have examined. 



Instructive results are obtained by considering the wave- 

 surface and the ray in the p space and their associated wave- 

 surface and ray in the actual p' space. If a disturbance 

 emanate from a point on the axis of the medium, its wave- 

 surface is a sphere both in the standard and actual positions 

 of matter, but the ray, while straight in the standard position, 

 is a diverging spiral in the actual position that circulates 

 round the axis, one complete revolution taking place while 

 the ray moves a distance 27rA in the direction of the axis. 



University of Tasmania, Hobart, 

 May 30, 1896. 



XXIII. On the Continuity of Isothermal Transformation from 

 the Liquid to the Gaseous State. By Thomas Preston, 

 M.A., F.R.U.L* 



WHEN any substance passes from the liquid to the 

 gaseous state by isothermal transformation, the 

 relation between pressure and volume is represented diagram- 

 matically by a curve such as that shown in fig. 1. In this 



Fig. 1. 



V 



curve, the part AB refers to the condition of the substance 

 in which it is altogether liquid, and along this part the volume 



* From the Trans. Roy. Dub. Soc. n. s. vol. vi. part iv. Ooumnuii- 

 cated by the Author. 



