[Sidenote: Progress from 1837 to 1887.]

I am conscious that in undertaking to progress give even the briefest
sketch of the progress of physical science, in all its branches,
during the last half-century, I may be thought to have exhibited more
courage than discretion, and perhaps more presumption than either. So
far as physical science is concerned, the days of Admirable Crichtons
have long been over, and the most indefatigable of hard workers may
think he has done well if he has mastered one of its minor
subdivisions. Nevertheless, it is possible for anyone, who has
familiarised himself with the operations of science in one department,
to comprehend the significance, and even to form a general estimate of
the value, of the achievements of specialists in other departments.

Nor is their any lack either of guidance, or of aids to ignorance. By
a happy chance, the first edition of Whewell's 'History of the
Inductive Sciences' was published in 1837, and it affords a very
useful view of the state of things at the commencement of the
Victorian epoch. As to subsequent events, there are numerous
excellent summaries of the progress of various branches of science,
especially up to 1881, which was the jubilee year of the British
Association.[D] And, with respect to the biological sciences, with
some parts of which my studies have familiarised me, my personal
experience nearly coincides with the preceding half-century. I may
hope, therefore, that my chance of escaping serious errors is as good
as that of anyone else, who might have been persuaded to undertake the
somewhat perilous enterprise in which I find myself engaged.

There is yet another prefatory remark which it seems desirable I
should make. It is that I think it proper to confine myself to the