Dr. Hare on the Cause of Heat. 143 
views which I shall here quote from his elements in order 
to introduce the subject more intelligibly. 
‘It seems possible” says the illustrious author “ to ac- 
count 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 
liquids 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 quick- 
ness; and that in ethereal substances, the particles move 
round their own axes, and separating from each other, pene- 
trate 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 great- 
er space ; and the dimunition 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 revolution of particles round their axes, at the mo- 
ment when the body becomes liquid or aeriform ; or from 
the loss of rapidity of vibration, in consequence of the mo- 
tion of the particles through greater space. 
“Ifa specific fluid of heat be admitted, it must be sup- 
posed liable to most of the affections which the particles of 
common matter are assumed to possess, to account for the 
phenomena; such as losing its motion when combining with 
bodies, producing motion when transmitted from one body 
to another, and gaining projectile notion when passing into 
free space ; so that many hypotheses must be adopted to 
account for its agency, which renders this view of the sub- 
ject less simple than the other. Very delicate experiments 
have been made, which show that bodies, when heated, do 
not increase in weight. This, as far as it goes, is an evi- 
dence against a subtile elastic fluid, producing the calorific 
expansion ; but it cannot be considered as decisive on ac- 
count of the imperfection of our instruments. A cubical 
inch of inflammable air requires a good balance to ascertain 
that it has any sensible weight, and a substance bearing the 
same relation to this, that this bears to platinum, could not 
perhaps be weighed by any method in our possession,” 
