Because all bodies contain _latent heat_, that is, heat that lies hid in their substance, and the rubbings of two bodies against each other _draws the latent heat to the excited surfaces_.
322. _Why does the rubbing of two surfaces together attract latent heat to those surfaces?_
Because it is a law of nature that _heat_ shall always attend _motion_; and it is generally found that the _intensity of heat_ bears a specific relation to the _velocity of motion_.
The _rays_ of the _sun_, the _currents_ of _electricity_, the _action_ of _chemicals_, and the _motion_ of _substances_.
Because its latent heat is partly _drawn off_ by the surrounding air.
Because the heat, once latent in the water, but drawn off by the air, _has returned_ to it, and restored the water to its former condition.
[Verse: "So teach us to number our days, that we may apply our hearts unto wisdom." PSALM XC.]
Because a larger amount of heat has entered into it than can remain latent in water. The water therefore expands and rises in the form of vapour, or _water attenuated by heat_.
327. _How many degrees of heat are latent, or hidden, in the different states of water?_
In thawing _ice_, 140 deg. of caloric become latent; and in converting the water into steam, 1,000 deg. more of caloric are be taken up. Therefore, _ice_ requires to take up 1,140 deg. of latent caloric before it becomes steam.
328. _What is the most modern theory of heat?_
It is this--that caloric, which produces heat, is an extremely _subtile fluid_, of so refined a nature that it possesses no weight, yet is capable of diffusing itself among the particles of the most solid bodies.
It is also believed that--all bodies are subject to the action of two opposing forces: one, the _mutual attraction_ of their _particles_; the other, the _repulsive force_ of _caloric_--and that bodies exist in the _æriform_, _fluid_, or _solid state_, _according to the predominance of either the one or the other of these opposing forces_.
329. _How do we measure the quantity of caloric in any substance?_
It is impossible to determine the amount of caloric which any body contains. Our _sensations_ would obviously be deceptive, since, if we dipped the right hand in snow, and held the left hand before the fire, and then immersed both hands in cold water, the water would feel _warm_ to the _right hand_ and _cold_ to the _left hand_.