SPECIFIC HEAT. By the specific heat of a body is meant the time it takes to cool from a certain given temperature to another given temperature, when placed in vacuo in a polished silver vessel. By some writers the specific heat of a body is supposed to be its " capacity for heat," as if heat, which is the undulation of an ethereal medium, could be stowed away among the particles of a body. Surely the notion of " capacity for heat" is absurd. That different bodies should require different times to pass from one temperature to another involves no difficulty of comprehension, and specific heat is simply the measure of the time required.
Dr. Graham says, " Of all liquid or solid bodies wat,er has much the greatest capacity for heat ; hence the sea, which covers so large a proportion of the globe, is a great magazine of heat, and has a beneficial influence iu equalizing atmospheric temperatiu.e. Mercury has a small specc heat, so that it is quickly heated or cooled ; another property which recommends it as a liquid for the ther mometer, imparting as it does great sensibility to the instrument." The reader may amuse himself by trying to state in a different form, and on the assumption of the undulatory theory of heat, the facts implied in the above sentence.
The time which a body takes either to become colder or hotter depends in great measure on the condition of its surface. If the surface be smooth, polished, and white, the time is increased ; if rough and black, the time is diminished. When an ethereal undula tion strikes the surface of a body, it depends upon the condition of the surface whether the undulation be continued among the particles of ether within the body, or whether it be reflected among those which are external to the body ; and conversely, when a body is contracting, and therefore radiating heat, it depends upon the con dition of its surface, whether the undulations of the ether within the body be communicated to the ether without it, or returned by internal reflexion among the ether within it. A smooth polished surface is favourable to the reflexion of undulations, and unfavourable to their direct propagation. Colour is no doubt owing to a pecu liarity of surface. See " Latent Heat."