And how do you ascertain the degrees of contraction of Wedgwood’s pyrometer?
MRS. B.
The dimensions of a piece of clay are measured by a scale graduated on the side of a tapered groove, formed in a brass ruler; the more the clay is contracted by the heat, the further it will descend into the narrow part of the tube.
Before we quit the subject of expansion, I must observe to you that, as liquids expand more readily than solids, so elastic fluids, whether air or vapour, are the most expansible of all bodies.
It may appear extraordinary that all elastic fluids whatever, undergo the same degree of expansion from equal augmentations of temperature.
EMILY.
I suppose, then, that all elastic fluids are of the same density?
MRS. B.
Very far from it; they vary in density, more than either liquids or solids. The uniformity of their expansibility, which at first may appear singular, is, however, readily accounted for. For if the different susceptibilities of expansion of bodies arise from their various degrees of attraction of cohesion, no such difference can be expected in elastic fluids, since in these the attraction of cohesion does not exist, their particles being on the contrary possessed of an elastic or repulsive power; they will therefore all be equally expanded by equal degrees of caloric.
EMILY.