These electricities seem to me to be a kind of chemical spirit, which animates the particles of bodies, and draws them together. EMILY. If it is known, then, with which of the electricities bodies are united, it can be inferred which will, and which will not, combine together? MRS. B. Certainly. --I should not omit to mention, that some doubts have been entertained whether electricity be really a material agent, or whether it might not be a power inherent in bodies, similar to, or, perhaps identical with, attraction. EMILY. But what then would be the electric spark which is visible, and must therefore be really material? MRS. B. What we call the electric spark, may, Sir H. Davy says, be merely the heat and light, or fire produced by the chemical combinations with which these phenomena are always connected. We will not, however, enter more fully on this important subject at present, but reserve the principal facts which relate to it to a future conversation. Before we part, however, I must recommend you to fix in your memory the names of the simple bodies, against our next interview. CONVERSATION II. ON LIGHT AND HEAT OR CALORIC. CAROLINE. We have learned by heart the names of all the simple bodies which you have enumerated, and we are now ready to enter on the examination of each of them successively. You will begin, I suppose, with LIGHT? MRS. B. Respecting the nature of light we have little more than conjectures. It is considered by most philosophers as a real substance, immediately emanating from the sun, and from all luminous bodies, from which it is projected in right lines with prodigious velocity. Light, however, being imponderable, it cannot be confined and examined by itself; and therefore it is to the effects it produces on other bodies, rather than to its immediate nature, that we must direct our attention. The connection between light and heat is very obvious; indeed, it is such, that it is extremely difficult to examine the one independently of the other. EMILY. But, is it possible to separate light from heat; I thought they were only different degrees of the same thing, fire? MRS. B. I told you that fire was not now considered as a simple element. Whether light and heat be altogether different agents, or not, I cannot pretend to decide; but, in many cases, light may be separated from heat. The first discovery of this was made by a celebrated Swedish chemist, Scheele. Another very striking illustration of the separation of heat and light was long after pointed out by Dr. Herschell. This philosopher discovered that these two agents were emitted in the rays of the sun, and that heat was less refrangible than light; for, in separating the different coloured rays of light by a prism (as we did some time ago), he found that the greatest heat was beyond the spectrum, at a little distance from the red rays, which, you may recollect, are the least refrangible. EMILY. I should like to try that experiment.