vacuum tube the "step up" current of the secondary coil with a
potential incalculably increased.

While Dr. Morton has in some of his experiments excited his Leyden
jars from an induction coil, he thinks the best promise lies in the
use of powerful Holtz machines; and he now uses no Leyden jars or
converters, thus greatly adding to the simplicity of operations.

In regard to the bulb, Dr. Morton has tested various kinds of vacuum
tubes, the ordinary Crookes tubes, the Geissler tubes, and has
obtained excellent results from the use of a special vacuum lamp
adapted by himself to the purpose. One of his ingenious expedients
was to turn to use an ordinary radiometer of large bulb, and, having
fitted this with tin-foil electrodes, he found that he was able to
get strongly marked shadow pictures. This application of the Röntgen
principle will commend itself to many students who, being unable to
provide themselves with the rare and expensive Crookes tubes, may
buy a radiometer which will serve their purpose excellently in any
laboratory supply store, the cost being only a few dollars, while the
application of the tin foil electrodes is perfectly simple.

In the-well equipped Jackson laboratory at Trinity College, Hartford,
I found Dr. W.L. Robb, the professor of physics, surrounded by
enthusiastic students, who were assisting him in some experiments with
the new rays. Dr. Robb is the better qualified for this work from
the fact that he pursued his electrical studies at the Würzburg
University, in the very laboratory where Professor Röntgen made his
great discovery. The picture reproduced herewith, showing a human foot
inside the shoe, was taken by Dr. Robb. The Crookes tubes used in this
and in most of Dr. Robb's experiments are considerably larger than any