588 
Latent Heat. 
[Odtobe 
resistance to impadt decreases in energy, through molecules 
being more and more obliged to depend on their individual 
motive powers, and less on assistance from their neighbours. 
But latent heat presents other phenomena, which it is 
necessary now to consider. Thus we find the specific heats 
of solids and gases are closely similar, while the specific heat 
of liquids is considerably greater than that of either solid or 
gas. How is this to be explained ? Must we consider that 
liquids decrease more rapidly in rigidity with increased heat, 
or can we conceive of any other cause ? The first explana- 
tion is hardly probable, and it may not be difficult to deduce 
a better one. It seems more probable that this behaviour 
towards specific heat of the three forms of matter points to 
a certain similarity in motive condition between solids and 
gases, and a diversity in liquids. That the conditions of 
heat impadt in solids and gases have a strong similarity we 
are well assured. In both cases it is diredt impadt of mole- 
cule upon molecule, these being free moving molecules in the 
gas and vibrating molecules in the solid. But it is very 
doubtful if this condition of diredt impadt exists in the liquid. 
If, as the writer is disposed to consider, the liquid state of 
matter consists in rotation around a centre of attraction, 
instead of a vibration between local attractions as in the 
solid, its motive energy becomes to some degree centripetal. 
Rotating particles could not meet the impact energy of solid 
and gaseous particles by a reverse impadt, and their resist- 
ance must partake of the nature of elasticity. They must 
retain their curves of rotation with a degree of inertia, whose 
vigour depends on the energy of central attraction, and must 
thus oppose an elastic resistance to the impact energy of 
exterior molecules. But the rate of decrease or increase 
with temperature of an energy of this kind might be very 
different from that of impact energy, and thus the specific 
heat be very different. In the illustration already given of a 
molecule attached to the centre of an elastic band, we would 
have, in the molecule of the solid, the double resistance of , 
the elasticity of the band and of its own moving energy ; in 
the liquid molecule the elasticity of the band only, since here 1 
the moving energy virtually converts the molecule into such 
a band. Possibly, then, the resistance of the molecules of 1 
the liquid would decrease more rapidly than that of the 
molecules of the solid and the gas, and its specific heat 
would be greater in consequence. The heat energy, which j 
is a centrifugal motion in the solid and the gas, may become 
partly or wholly a centripetal motion in the liquid. 
But our review of latent heat by no means stops here* 
