, 1905 to 1912; which, indeed, for modern
purposes has superseded the above-mentioned works. In passing we would
remark that the 'national' of its title-page is in the wider sense of the
term.

And here a word of warning. Always make a point of entering the _errata_
with a pencil in the margins of every reference-book that you acquire. Do
this before you assign a place to the volume on the shelf; otherwise you
may quote or condemn a passage or date which has been rendered wrongly
owing to a clerical or printer's error, and has been put right in the
_errata_.[56] Need we say that this practice should not necessarily be
confined to works of reference? One may even find some amusement here.
Was it not Scarron who wrote a poem, 'A Guillemette, chienne de ma
soeur,' but quarrelling with his sister just as the volume was about to
appear, put in the _errata_, 'For _chienne de ma soeur_ read _ma
chienne de soeur_'!

All these works will assuredly impart to the book-collector much
knowledge of ancient books and their attributes, but he will still be at
sea with regard to that most necessary part of their collection, namely,
their commercial value. There is only one way in which this knowledge may
be obtained, and that is by the study of catalogues. To arrive at a
proper estimate of a book's value from the purely financial point of
view, a close study of booksellers' catalogues and auction-sale prices
through many years is necessary. The divergence in price of identical
works is somewhat disturbing at first to the novice, and it is only after
some considerable experience and the actual handling of books that one is
enabled to arrive at a proper estimate of their worth. 'Continual use
gives men a judgment of things comparatively, and they come to fix on
what is most proper and easy, which no man, upon cursory view, would
determine.'[57]

Before the writer are two catalogues, one from a country bookseller, the
other from a well-known London house. Each contains a copy of the
'Thesaurus Cornucopiae et Horti Adonidis,' printed by Aldus Manutius in
1496. The former offers it for 25s., the latter for L25. Why this
extraordinary difference in price?

The reasons are ample. The London copy has this description:

'Fol.; 16th cent. English binding of brown calf, gilt borders and
centre-pieces, g.e. (by THOMAS BERTHELET, the Royal binder), in
fine condition: beautiful copy, perfectly clean and large, 320 x
215 m.m.