PLEASURES OF SCIENCE. 17 



Natural Philosophy, but more properly Mechanical Philosophy,} in- 

 vestigates the sensible motions of all bodies. The second investigates 

 the constitution and qualities of all bodies, and has various names, 

 according to its different objects. It is called Chemistry, if it teaches 

 the properties of bodies with respect to heat, mixture together, weight, 

 taste, appearance, and so forth : Anatomy and Animal Physiology, if 

 it teaches the structure and functions of living bodies, especially the 

 human, for when it shows those of other animals, we term it Compara- 

 tive Anatomy : Medicine, if it teaches the nature of diseases, and the 

 means of preventing them and of restoring health : Zoology, (from the 

 Greek words signifying to speak of animals,) if it teaches the arrange- 

 ment or classification and the habits of the different lower animals : 

 Botany, if it teaches the arrangement or classification and habits of 

 plants : Geology, (from the Greek words meaning to speak of the earth,) 

 including Mineralogy, if it teaches the arrangement of minerals, the 

 structure of the masses in which they are found, and of the earth com- 

 posed of those masses. The term Xatural History is given to the 

 three last branches taken together, but chiefly as far as relates to the 

 classification of different things, or the observation of the resemblances 

 and differences of the various animals, plants, and inanimate and 

 ungrowing substances in nature. 



But here we may make two general observations. Thejirst is, that 

 every such distribution of the sciences is necessarily imperfect ; for one 

 runs unavoidably into another. Thus, Chemistry shows the qualities 

 of plants with relation to other substances, and to each other ; and 

 Botany does not overlook those same qualities, though its chief object 

 be arrangement. So Mineralogy, though principally conversant with 

 classifying metals and earths, yet regards also their qualities in respect 

 of heat and mixture. So, too, Zoology, beside arranging animals, 

 describes their structures, like Comparative Anatomy. In truth, all 

 arrangement and classifying depends upon noting the things in which 

 the objects agree and differ ; and among those things, in which ani- 

 mals, plants, and minerals agree, must be considered the anatomical 

 qualities of the one and the chemical qualities of the other. From 

 hence, in a great measure, follows the second observation, namely, that 

 the sciences mutually assist each other. We have seen how Arithmetic 

 and Algebra aid Geometry, and how both the purely Mathematical 

 Sciences aid Mechanical Philosophy. Mechanical Philosophy, in like 

 manner, assists, though, in the present state of our knowledge, not very 

 considerably, both Chemistry and Anatomy, especially the latter ; and 

 Chemistry very greatly assists both Physiology, Medicine, and all the 

 branches of Natural History. 



The first great head, then, of Xatural Science, is Mechanical Philo- 

 sophy ; and it consists of various subdivisions, each forming a science 

 of great importance. The most essential of these, and which is indeed 

 fundamental, and applicable to all the rest, is called Dynamics, from 

 the Greek word signifying power or force, and it teaches the laws of 

 motion in all its varieties. The case of the stone thrown forward, 

 which we have already mentioned more than once, is an example. 

 Another, of a more general nature, but more difficult to trace, and far 

 more important in its consequences, and of which, indeed, the former 



B 



