As I suspected Brown had indeed written earlier about card
catalogues, in 'The Library', v.6, 1894, 'Mechanical Methods
of Displaying Catalogues and Indexes', relevant pages 49-54.
In this he gives more detail about the origin of the card
for cataloguing and indexing purposes - not perhaps precisely
the same as the card catalogue - suggesting mid to late 18th
century France, inc. the Bibliotheque National. He also cites
a paper given at the LA Conference in Paris (I think - I know
the LA did hold its conference there once around that time -
no time to check!) in 1892 by Richard Prosser. He also notes a
reference to Trinity College Dublin using cards 'early in the
present century' as stated in a paper at the London Conference
of Librarians in 1877. But again no reference to size.

Following up the Dewey lead, I checked our run of Dewey's very
practically based periodical 'Library Notes', and lo and behold
in vol.1, no., 1886 are some comments by Dewey on 'Card Catalogs',
inc. comments on size (pp.33-6). Here Dewey writes: 'the size of
a card should not be smaller than the standard index 5 by 12 1/2
cm. or larger than the standard postal card 7 1/2 by 12 1/2cm.
So, there we have Dewey's statements, in metric. However he goes
on to link this to the work of the American Library Association's
Co-operation Committe, set up at the ALA's inaugural meeting in
1876. They recommended the former size, although Dewey comments
that there has recently been a growing trend towards the bigger size.

So, back I went to vol.1 of the 'American Library Journal' (as it
was then known) for 1876. Pages 285-6 indeed have the report of
the Co-operation Committee, which did not include Dewey, recommending
the 5 by 12 1/2 size card. Indeed so anxious were they that this
should become standard, that the ALA via its Library Supplies division
in Boston, which I believe was the brainchild of and run by Dewey
(again, no time to check) went into mass production of the 5 by 12
1/2 cm card, as shown by an advert from them for the 'Standard
Catalogue (sic.) Card' (p.346). 50,000 cards then cost $1.75 per
thousand.

Not quite a full answer, as we are still left with nailing when
and why the card changed from the smaller to the bigger size,
as mentioned in Geoffrey Robinson's original query. Dewey did
however suggest that there was a move in that direction by 1886,
as the bigger size allowed more room for notes on the cards. In
his 1886 article he also noted that 'the printed titles which
will be issued by the new publishing section (run by Dewey?) of
the (American) Library Association will be of the postal (i.e. the
bigger) size'.

Now to make the link between catalogue cards, size, Otlet and Dewey.
I wonder who attended the 1892 LA Conference in Paris I referred to
 above?

Quite good fun for a Friday afternoon actually!

Chris Baggs,
Aberystwyth