_Eub_.--I am glad that our opposition has led you to so complete a vindication of your favourite science. I want no further proof of its utility. I regret that I have not before made it a particular object of study. _Phil_.--As our friend has so fully convinced us of the importance of chemistry, I hope he will descend to some particulars as to its real nature, its objects, its instruments. I would willingly have a definition of chemistry and some idea of the qualifications necessary to become a chemist, and of the apparatus essential for understanding what has been already done in the science, and for pursuing new inquiries. _The Unknown_.--There is nothing more difficult than a good definition, for it is scarcely possible to express in a few words the abstracted view of an infinite variety of facts. Dr. Black has defined chemistry to be that science which treats of the changes produced in bodies by motions of their ultimate particles or atoms, but this definition is hypothetical, for the ultimate particles or atoms are mere creations of the imagination. I will give you a definition, which will have the merit of novelty and which is probably general in its application. Chemistry relates to those operations by which the intimate nature of bodies is changed, or by which they acquire new properties. This definition will not only apply to the effects of mixture, but to the phenomena of electricity, and, in short, to all the changes which do not merely depend upon the motion or division of masses of matter. However difficult it may have been to have given you a definition of chemistry, it is still more difficult to give you a detail of all the qualities necessary for a chemical philosopher. I will not name as many as Athenaeus has named for a cook, who, he says, ought to be a mathematician, a theoretical musician, a natural philosopher, a natural historian, &c., though you had a disposition just now to make chemistry merely subservient to the uses of the kitchen. But I will seriously mention some of the studies fundamental to the higher departments of this science; a man may be a good practical chemist perhaps without possessing them, but he never can become a great chemical philosopher. The person who wishes to understand the higher departments of chemistry, or to pursue them in their most interesting relations to the economy of Nature, ought to be well-grounded in elementary mathematics; he will oftener have to refer to arithmetic than algebra, and to algebra than to geometry. But all these sciences lend their aid to chemistry; arithmetic, in determining the proportions of analytical results and the relative weights of the elements of bodies; algebra, in ascertaining the laws of the pressure of elastic fluids, the force of vapour as dependent upon temperature, and the effects of masses and surfaces on the communication and radiation of heat; the applications of geometry are principally limited to the determination of the