Hence what is called _Warmth_ in Wool, and its Preference
on that Account to Linen; Wool not being so good a Conductor. And
hence all the natural Coverings of Animals to keep them warm, are
such, as retain and confine the natural Heat in the Body, by being
bad Conductors; such as Wool, Hair, Feathers, and the Silk by which
the Silk-worm in its tender embrio State is first cloathed.
Cloathing, thus considered, does not make a Man warm, by _giving_
Warmth, but by preventing the too quick Dissipation of the Heat
produc'd in his Body, and so occasioning an Accumulation.
There is another curious Question I will just venture to touch
upon, viz. Whence arises the sudden extraordinary Degree of Cold,
perceptible on mixing some Chymical Liquors, and even on mixing Salt
and Snow, where the Composition appears colder than the coldest of
the Ingredients? I have never seen the chymical Mixtures made, but
Salt and Snow I have often mixed myself, and am fully satisfied that
the Composition feels much colder to the Touch, and lowers the
Mercury in the Thermometer more than either Ingredient would do
separately. I suppose with others, that Cold is nothing more than an
Absence of Heat or Fire. Now if the Quantity of Fire before
contain'd or diffus'd in the Snow and Salt, was expell'd in the
Uniting of the two Matters, it must be driven away either thro' the
Air or the Vessel containing them.
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