IN THE LAST HALF-CENTURY. 101 



on the one hand, and degrees of pressure 

 and of heat on the other. Almost all, 

 even the most refractory, solids have been 

 vaporised by the intense heat of the elec- 

 tric arc ; and the most refractory gases 

 have been forced to assume the liquid, 

 and even the solid, forms by the combina- 

 tion of high pressure with intense cold. 

 It has further been shown that there is no 

 discontinuity between these states — that a 

 gas passes into the liquid state through a 

 condition which is neither one nor the 

 other, and that a liquid body becomes 

 solid, or a solid liquid, by the intermedia- 

 tion of a condition in which it is neither 

 truly solid nor truly liquid. 



Theoretical and experimental investi- 

 gations have concurred in the establish- 

 ment of the view that a gas is a body, the 

 particles of which are in incessant recti- 

 linear motion at high velocities, colliding 

 with one another and bounding back when 

 they strike the walls of the containing 



