His best results have
been obtained with long exposures--an hour or an hour and a half--and
he regards it as of the first importance that the objects through
which the Roentgen rays are to be projected be placed as near as
possible to the sensitized plate.
It is from a failure to observe this precaution that so many of the
shadow pictures show blurred outlines. It is with these pictures as
with a shadow of the hand thrown on the wall--the nearer the hand
is to the wall, the more distinct becomes the shadow; and this
consideration makes Professor Wright doubt whether it will be
possible, with the present facilities, to get clearly cut shadow
images of very thick objects, or in cases where the pictures are
taken through a thick board or other obstacle. The Roentgen rays will
doubtless traverse the board, and shadows will be formed upon the
plate, but there will be an uncertainty or dimness of outline that
will render the results unsatisfactory. It is for this reason that
Professor Wright has taken most of his shadow pictures through only
the thickness of ebonite in his plate-holder. A most successful shadow
picture taken by Professor Wright in this way, shows five objects laid
side by side on a large plate--a saw, a case of pocket tools in their
cover, a pocket lense opened out as for use, a pair of eye-glasses
inside their leather case, and an awl.
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