are considered together. Without this there can be no conception of the
limitations imposed upon him in his chosen life's work. The mere amount
of his research is greatly magnified by the smallness of the time
allowed for it.

But great as was the impression left by these researches in purely
scientific circles, it is not by them alone that he made his impression
upon the mass of his contemporaries. They were chiefly moved by
something over and above his wide knowledge in so many fields--by his
passionate sincerity, his interest not only in pure knowledge, but in
human life, by his belief that the interpretation of the book of nature
was not to be kept apart from the ultimate problems of existence; by the
love of truth, in short, both theoretical and practical, which gave the
key to the character of the man himself.

Accordingly, I have not discussed with any fulness the value of his
technical contributions to natural science; I have not drawn up a
compendium of his philosophical views. One is a work for specialists;
the other can be gathered from his published works. I have endeavoured
rather to give the public a picture, so far as I can, of the man
himself, of his aims in the many struggles in which he was engaged, of
his character and temperament, and the circumstances under which his
various works were begun and completed.

So far as possible, I have made his letters, or extracts from them, tell
the story of his life. If those of any given period are diverse in tone
and character, it is simply because they reflect an equal diversity of
occupations and interests. Few of the letters, however, are of any great
length; many are little more than hurried notes; others, mainly of
private interest, supply a sentence here and there to fill in the