An Elementary Treatise On Heat

e first of these the expansion of uncrystallized solids will be considered, while in the second the behaviour of crystals under change of temperature will be shortly described. DILATATION OF UNCRYSTALLIZED SOLIDS. 33. In some cases it is the increment of the volume of a body that we wish to estimate, while in others, as for instance when we are considering a substance, such as a bar, of which the length is the important element, it is change of length and not change of volume with which we concern ourselves. The former of these is called linear and the latter cubical dilatation or expansion. We shall commence with linear expansion : but let us first proceed to define what is meant by " the coefficient of expansion," whether linear or cubical. The coefficient of expansion of a substance is the expansion for one degree of temperature of that quantity of the substance whose length or volume (asthe case may be) was unity at a certain standard temperature, as for instance at the temperature of melting ice. Thus if the length of a brass bar be unity at 32 Fahr., at 33 it will be 1.00001: hence .00001 is the linear coefficient of expansion of brass for 1 Fahr. 34. Linear dilatation. Lavoisier's method. Several methods of finding the linear dilatation of solids have been proposed. In one of these, namely that adopted by Lavoisier and Laplace, a telescope is placed upon a horizontal axis between two pillars, as in Fig. 8. This axis carries a cross piece AB r...