1833.] Attraction and Repulsion. 459 
philosopher* has extended the views of Bacon, and has endeavoured to 
explain all the phenomena of repulsion by a vibratory and rotatory mo- 
tion in the particles of bodies. This great and meritorious author writes 
in these words :—‘‘ When any body iscooled, it occupies asmaller volume 
than before, it is evident, therefore, that its parts must have approached 
towards each other ; when the body is expanded by heat, it is equally 
evident, that its parts must have separated from each other. The im- 
mediate cause of the phenomena of heat then is motion, and the laws 
of its communication are precisely the same, as the laws of the commu- 
nication of motion.” Since all matter may be made to fill a smaller 
volume by cooling, it is evident that the particles of matter must have 
space between them, and since every body can communicate the power 
of expansion to a body of a lower temperature; that is, can give an ex- 
pansive motion to its particles, it is a probable inference, that its own 
particles are possessed of motion: but as there is no change in the posi- 
tion of its parts, as long as its temperature is uniform, the motion, if it 
exist, must be a vibratory or undulatory motion, or a motion of the par- 
ticles round their axes, or a motion of particles round each other.” 
And, he continues, ‘‘ It seems possible, to account for all the pheno- 
mena 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 consequence of the revo- 
lution of particles round their axes, at the moment when the body be- 
comes fluid or aériform, or from the loss of the rapidity of vibration, 
in consequence of the motion of the particles through greater space.” 
It is under the deepest impression of respect for the author that I 
allow myself to make my observations on the doctrine supported in the 
above quotation, which observations are only stated from a persuasion 
of the importarce of one decided and general opinion as to the nature 
of heat in forming the science of chemical philosophy. 
* Sir H. Davy’s Elements of Chemical Philosophy. 
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