



THE PROGRESS OF SCIENCE 105 



have been forced to assume the liquid, and even 

 the solid, forms by the combination 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 intermediation of a 

 condition in which it is neither truly solid nor 

 truly liquid. 



Theoretical and experimental investigations 

 have concurred in the establishment of the view 

 that a gas is a body, the particles of which are in 

 incessant rectilinear motion at high velocities, col- 

 liding with one another and bounding back when 

 they strike the walls of the containing vessel ; and, 

 on this theory, the already ascertained relations of 

 gaseous bodies to heat and pressure have been 

 shown to be deducible from mechanical principles. 

 Immense improvements have been effected in the 

 means of exhausting a given space of its gaseous 

 contents ; and experimentation on the phenomena 

 which attend the electric discharge and the action 

 of radiant heat, within the extremely rarefied media 

 thus produced, has yielded a great number of re- 

 markable results, some of which have been made 

 familiar to the public by the Gieseler tubes and 

 the radiometer. Already, these investigations have 

 afforded an unexpected insight into the constitu- 

 tion of matter and its relations with thermal and 



