many of his researches were allowed to drop, and only resumed after an
interval of years. Thus a rigidly chronological series of letters would
present a patchwork of subjects, each of which would be difficult to
follow. The Table of Contents will show in what way I have attempted to
avoid this result.

In printing the letters I have followed (except in a few cases) the usual
plan of indicating the existence of omissions or insertions. My father's
letters give frequent evidence of having been written when he was tired or
hurried, and they bear the marks of this circumstance. In writing to a
friend, or to one of his family, he frequently omitted the articles: these
have been inserted without the usual indications, except in a few
instances, where it is of special interest to preserve intact the hurried
character of the letter. Other small words, such as "of", "to", etc., have
been inserted usually within brackets. I have not followed the originals
as regards the spelling of names, the use of capitals, or in the matter of
punctuation. My father underlined many words in his letters; these have
not always been given in italics,--a rendering which would unfairly
exaggerate their effect.

The Diary or Pocket-book, from which quotations occur in the following
pages, has been of value as supplying a frame-work of facts round which
letters may be grouped. It is unfortunately written with great brevity,
the history of a year being compressed into a page or less; and contains
little more than the dates of the principal events of his life, together
with entries as to his work, and as to the duration of his more serious
illnesses. He rarely dated his letters, so that but for the Diary it would
have been all but impossible to unravel the history of his books. It has
also enabled me to assign dates to many letters which would otherwise have
been shorn of half their value.