1901.] on Gases at the Beginning and End of the Century. 731 



would doubtless lose their elasticity for want of a sufficient tempera- 

 ture to retain them in that state ; they would return to the fluid st;ite 

 of existence, and new liquids would be formed of whose properties 

 we canuot at present form the most distant idea." 



Dalton, in his paper ' On the force of steam or vapour from water 

 and various other liquids both in a vacuum and in air,' published in 

 1802, arrived at the conclusion that, " there can scarcely be a doubt 

 entertained respecting the reducibility of all elastic fluids of what- 

 ever kind into liquids ; and we ought not to despair of effecting it in 

 low temperature and by strong pressure exerted upon the unmixed 

 gases." Here we notice Dalton introduces the novelty of suggesting 

 the application of combining high pressure and low temperature on 

 the pure gases, which led in 1823 to the successful experiments of 

 Northmore, and then of Faraday and Davy. Thomas Young, in the 

 lectures he delivered in this Institution early in the last century, and 

 subsequently published, in 1807, under the title ' A Course of Lectures 

 on Natural Philosophy and the Mechanical Arts,' after a careful 

 analysis of all the existing experimental data, strongly supported the 

 view that heat was a quality of the particles of bodies, and that that 

 quality could only be motion. In explanation of the action of heat 

 he says, " The effects of heat on the cohesive and repulsive powers of 

 bodies have sometimes been referred to the centrifugal forces and 

 mutual collisions of the revolving and vibrating particles ; and the 

 increase of the elasticity of aeriform fluids has been very minutely 

 compared with the force which would be derived from an acceleration 

 of these internal motions." (Young, 1807.) In the 'Elements of 

 Chemical Philosophy,' published in 1812, Davy, in order to guard 

 against the supposition that the doctrine of a specific fluid of heat 

 was a necessary part of the principles of philosophical chemistry, 

 threw out the following suggestions as the basis of a rational theory 

 of the causes inducing change of state in matter ; following the dictum, 

 that the immediate cause of the phenomenon of heat is motion. Thus 

 he says, " It seems possible to account for all the phenomena of heat 

 if it be supposed that in solids the particles are in a constant state of 

 vibratory motion, the particles of the hottest bodies moving with the 

 greatest velocity and through the greatest space ; that in fluids and 

 elastic fluids, besides the vibratory motion, which must be conceived 

 greatest in the last, the particles have a motion round their own axes 

 with different velocities, the particles of elastic fluids moving with 

 the greatest quickness ; and that in ethereal substances the particles 

 move round their own axes, and separate from each other, penetrating 

 in right lines through space. Temperature may be conceived to 

 depend upon the velocities of the vibrations ; increase of capacity on 

 the motion being performed in greater space, and the diminution of 

 temperature during the conversion of solids into fluids or gases, may 

 be explained on the idea of the loss of vibratory motion in conse- 

 quence of the revolution of particles round their axes at the moment 

 when the body becomes fluid or aeriform, or from loss of rapidity of 

 vibration in consequence of the motion of the particles through greater 



