and about five inches in diameter--the one
with which he has taken all his shadow pictures. 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. As will be seen from the
accompanying reproduction of this picture, all the objects are
photographed with remarkable distinctness, the leather case of the
eye-glasses being almost transparent, the wood of the handles of the
awl and saw being a little less so, while the glass in the eye-glasses
is less transparent than either. In the case of the awl and the saw,
the iron stem of the tool shows plainly inside the wooden handle. This
photograph is similar to a dozen that have been taken by Professor
Wright with equal success. The exposure here was fifty-five minutes.

A more remarkable picture is one taken in the same way, but with a
somewhat longer exposure--of a rabbit laid upon the ebonite plate, and
so successfully pierced with the Roentgen rays that not only the bones
of the body show plainly, but also the six grains of shot with which
the animal was killed. The bones of the fore legs show with beautiful
distinctness inside the shadowy flesh, while a closer inspection makes
visibl