en made on the tinted 'cathedral' glasses of
Messrs. Pilkington Bros., Limited, with the result that Nos. 812 and
712 afforded almost complete protection during two months' exposure to
sunlight, while Nos. 704 and 804 may be recommended where only very
pale shades are permissible. The glasses employed were subjected to
careful spectroscopic examination, and to colour-measurement by the
tintometer, but neither were found to give precise indications as to
the protective power of the glasses, which is no doubt due to the
absorption of the violet, and especially of the invisible ultra-violet
rays. An easy method of comparing glasses is to expose under them to
sunlight the ordinary sensitised albumenised photographic paper.
Those glasses under which this is least darkened are also most
protective to leather."

_Tobacco._--Smoking was found to be injurious, and it is certainly a
mistake to allow it in libraries.

"The effect of ammonia vapour, and tobacco fumes, of which ammonia is
one of the active ingredients, was also examined. The effect of
ammonia fumes was very marked, darkening every description of leather,
and it is known that in extreme cases it causes a rapid form of decay.
Tobacco smoke had a very similar darkening and deleterious effect
(least marked in the case of sumach tanned leathers), and there can be
no doubt that the deterioration of bindings in a library where smoking
was permitted and the rooms much used, must have been partly due to
this cause."

_Damp._--Books kept in damp places will develop mildew, and both
leather and paper will be ruined.

Where possible, naturally dry rooms should be used for libraries, and
if not naturally dry, every means possible should be taken to render
them so. It will sometimes be found that the only way to keep the
walls of an old house dry is to put in a proper dampcourse. There are
various other methods employed, such as lining the walls with thin
lead, or painting them inside and out with some waterproofing
preparation: but as long as a wall remains in itself damp, it is
doubtful if any of these things will permanently keep the damp from
penetrating.

Bookshelves should never be put against the wall, nor the books on the
floor. There should always be space for air to circulate on all sides
of the bookshelves. Damp is specially injurious if books are kept
behind closely-fitting doors. The doors of bookcases should be left
open from time to time on warm days.

Sho