In making carbon transparencies for instance, the
gelatine film which is squeegeed against the glass necessarily takes its
dimensions from the paper to which it is attached, and if that be
expanded more in the one direction than another, the transparency is
similarly deformed; and so, of course, is any negative, enlarged or
otherwise, produced in the camera therefrom. A reproduced negative by
contact printing may either have the distortion due to expansion of the
paper bearing the gelatine film removed or doubled, according to the
direction in which the paper is used for the new negative.--_W.E.
Debenham, in Br. Jour. of Photography_.
* * * * *
MEASURING THE THICKNESS OF BOILER PLATES.
An ingenious process for determining the thickness of iron plates in
boilers, or places where they cannot otherwise be measured without
cutting them, has been invented by M. Lebasteur. He spreads upon the
plate the thickness of which he desires to find, and also upon a piece of
sheet iron of known thickness, a layer of tallow about 0.01 inch thick.
He then applies to each, for the same length of time, a small object,
such as a surgeon's cauterizing instrument, heated as nearly as possible
to a constant temperature.
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