Page:Supplement to the fourth, fifth, and sixth editions of the Encyclopaedia Britannica - with preliminary dissertations on the history of the sciences - illustrated by engravings (IA gri 33125011196181).pdf/27

Rh great extension and improvement of Chemical knowledge, since the period when the corresponding article in the Encyclopædia was compiled. Farther, in conformity with the plan of that work, two subordimate heads of the science, requiring a fuller explanation than they could conveniently receive in the general treatise, are here discussed in separate articles. The first relates to the great doctrine of definite proportions in chemical combinations, which is explained under the head of Atomic Theory; the other, to the analysis of chemical substances and compounds, for the purpose of discovering their constituent principles, which is treated under Decomposition, Chemical. For these elaborate articles, and several others of great practical utility, in the department of the Chemical Arts and Manufactures, the work is indebted to Dr Thomas Thomson.

Every branch of Natural History has received contributions in the present work. Under Mineralogy, there is a systematic view of that branch, founded upon an arrangement derived from the external characters of minerals, lately instituted by Professor Mohs of Freiberg; an arrangement which receives additional credit from its adoption by the distinguished Mineralogist by whom it is here illustrated—Professor Jameson. Besides Mineralogy, properly so called, this article includes a brief summary of Geology; one of the most interesting topics of geological inquiry, that which relates to Organic Remains, being, however, reserved for a separate article; also written by Professor Jameson.

Botany is treated in a very instructive article by Sir James Edward Smith; in which, referring to the Encyclopædia for the details of systematic arrangement, he takes a general view of the progress of the science; of the different modes in which it has been cultivated; of the philosophy of its methods; and of the comparative advantages of the artificial and natural systems of Classification. The study of Plants is farther elucidated, in two articles upon their structure and functions; both of them written by Mr Ellis, and possessed of every recommendation that a thorough knowledge of the subject and luminous arrangement can impart. These articles are given under the heads of Anatomy, Vegetable, and Vegetable Physiology.

As the Zoological department of the Encyclopædia is founded chiefly upon the Linnæan classification of the animal kingdom, it was intended, both to add the recent discoveries, and to introduce an arrangement more agreeable to the