The most necessary thing now is to find some
means of producing streams of Roentgen rays of greater volume and
intensity, so as to make possible greater penetration and distinctness
in the images. Thus far only small Crookes tubes have been used, and
much is to be expected when larger ones become available; but there
is great difficulty in the manufacture of them. It might be possible,
Professor Wright thinks, to get good results by using, instead of the
Crookes tube, a large sphere of aluminium, which is more transparent
to the new rays than glass and possesses considerable strength. It is
a delicate question, however, whether the increased thickness of metal
necessary to resist the air pressure upon a vacuum would not offset
the advantage gained from the greater size. Moreover, it is a matter
for experiment still to determine, what kind of an electric current
would be necessary to excite such a larger tube with the best results.
Among the most important experiments in shadow photography made thus
far in America are those of Dr. William J. Morton of New York, who was
the first in this country to use the disruptive discharges of
static electricity in connection with the Roentgen discovery, and to
demonstrate that shadow pictures may be successfully taken without the
use of Crookes tubes.
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