Processes or laws cannot, however, be satisfactorily demonstrated in a museum; therefore such branches of knowledge as deal chiefly with these, as Astronomy, Geology (in the stricter sense of the word), and the experimental sciences, as Physics, Chemistry and Physiology, though essentially belonging to the domain of Natural History, have not found a place in the Natural History Museum. It is only the results of the working of these processes or laws, as shown in the modifications of the arrangement of the elementary substances of which the material of the Universe is composed, which can be fully illustrated by specimens admitting of being readily preserved and permanently exhibited in a museum. A Natural History Museum, therefore, in the sense in which the term is now usually understood, is a collection of the various objects, animate and inanimate, found in a state of nature. It will be readily understood that as the study of such objects is one of the principal means by which the laws leading to their formation or arrangement may be traced out, it is of the utmost importance for the progress of those departments of knowledge which the Museum is designed to cultivate, to bring together as full an illustrative series of these objects as possible. [Sidenote: Division into Mineral, Vegetable, and Animal.] Although the validity of the division of natural objects into _inorganic_ and _organic_ or _living_ has been the subject of some discussion, and although the separation of the latter into _vegetable_ and _animal_ is less absolute than was once supposed, yet for practical purposes, MINERAL, VEGETABLE, and ANIMAL remain the three great divisions or “kingdoms” into which natural bodies are grouped, and this classification has formed the basis of the arrangement of the collections in the Museum. [Sidenote: Mineral Department.] I. Inorganic substances occur in nature in a gaseous, liquid, or solid form. With few exceptions, it is only in the latter state that they can be conveniently preserved and exhibited in a museum, and it is to such that the term “mineral” is commonly limited. The collection, classification, and exhibition of specimens of this kind is the office of the Mineral Department of the Museum, to which is devoted the large gallery on the first floor of the east wing of the building. [Sidenote: Botanical Department.] II. The study of the vegetable kingdom, so far as it can be illustrated by preserved specimens, is the province of the Department of Botany, which occupies the upper floor of the east wing. [Sidenote: Zoological Department.] [Sidenote: Entomological Department.] III. In the same way the animal kingdom belongs to the Department of Zoology, from which it has been found necessary to separate an Entomological Department. To these two is assigned the whole of the western wing of the building. [Sidenote: Geological Department.]