i88i.1 
Latent Heat. 
585 
and some writers deny that the force condition which it indi- 
cates is in any proper sense allied to Heat, and claim that 
it should be expressed by some distinctive word. 
Yet these writers have given no satisfactory hypothesis to 
the contrary, and it remains probable that Latent Heat is 
but a special modification of heat energy. I have already 
briefly given my views concerning it, in the April number of 
the Journal, but will here partly repeat them in order to 
deduce certain important and interesting consequences of 
the principle of Latent Heat. 
Latent Heat, in its usual signification, is the heat which 
disappears when the solid is converted into the liquid, and 
the liquid into the gaseous form of matter, and which re- 
appears in the reverse process. Yet it has a much wider 
significance than this, since these radical changes in the 
condition of matter are by no means necessary to its exist- 
ence. Every apparent loss of heat in change of material 
condition is a conversion of sensible into latent heat. Thus 
as solids and liquids grew hotter their Specific Heat is said 
to increase. By this we mean that it takes more heat to 
produce a certain temperature effect at high than at low 
degrees of temperature. Part of the heat disappears, or 
becomes latent ; or, in other words, it needs different volumes 
of heat motion to produce unit effects of temperature when 
matter is in different states, or in different temperatures of 
the same state. But this gives us no just reason to conclude 
either that motion has gone out of or come into existence, 
has changed into something that is not motion, or has lost 
its centrifugal and assumed centripetal relations. It may 
continue to exist as centrifugal motive energy, and fail to 
make its existence felt as vigorously in high as in low tem- 
peratures for some sufficient reason. 
This reason, as considered in my article above referred to. 
maybe a mere difference of resisting energy in the molecules 
of matter. The effedt of a blow does not depend solely on 
the weight of the stick, but partly on the energy of the 
muscles which wield the stick. So a molecule which is 
strongly bound by attraction to other molecules, or vigorously 
wielded, as we may say, by other molecules, strikes a heavier 
blow than one which is weakly bound or feebly wielded. 
The first represents a moving stick with a strong arm behind 
it ; the second, the same stick with a weak arm. The blow 
of the first receives much more exterior aid than that of the 
second, and is therefore more effective. To produce equal 
effects the stick wielded by the weak arm must have greater 
weight, or must have a more vigorous original motion of its 
VOL. III. (THIRD SERIES). 2 Q 
