262 FRAGMENTS OF SCIENCE. 



its position in a series to which uniform experience assures 

 him it must belong. He regards all that he witnesses in 

 the present as the efflux and sequence of something that 

 lias gone before, and as the source of a system of events 

 which is to follow. The notion of spontaneity, by which 

 in his ruder state he accounted for natural events, is 

 abandoned; the idea that Nature is an aggregate of in- 

 dependent parts also disappears, as the connection and 

 mutual dependence of physical powers become more and 

 more manifest: until he is finally led to regard Nature as 

 an organic whole as a body each of whose members sym- 

 pathizes with the rest, changing, it is true, from age to 

 age, but changing without break of continuity in the rela- 

 tion of cause and effect. 



The system of things which we call Nature is, however, 

 too vast and various to be studied first-hand by any single 

 mind. As knowledge extends there is always a tendency 

 to subdivide the field of investigation. Its various parts 

 are taken up by different minds, and thus receive a greater 

 amount of attention than could possibly be bestowed en 

 them if each investigator aimed at the mastery of the whole. 

 The centrifugal form in which knowledge, as a whole, ad- 

 vances, spreading ever wider on all sides, is due in reality to 

 the exertions of individuals, each of whom directs his efforts, 

 more or less, along a single line. Accepting, in many re- 

 spects, his culture from his fellow-men taking it from 

 spoken words or from written books in some one direction, 

 the student of Nature ought actually to touch his work. 

 He may otherwise be a distributor of knowledge, but not 

 a creator, and he fails to attain that vitality of thought, 

 and correctness of judgment, which direct and habitual 

 contact with natural truth can alone impart. 



One large department of the system of Nature which 

 forms the chief subject of my own studies, and to which 

 it is my duty to call your attention this evening, is that of 

 physics, or natural philosophy. This term is large enough 

 to cover the study of Nature generally, but it is usually re- 

 stricted to a department which, perhaps, lies closer to our 

 perceptions than any other. It deals with the phenomena 

 and laws of light and heat with the phenomena and laws 

 of magnetism and electricity with those of sound with 

 the pressures and motions of liquids and gases, whether at 

 rest or in a state of translation or of undulation. The 



