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 
has 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 on 
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 
