me up, I made
the first fluoroscope, using tungstate of calcium. I also found that
this tungstate could be put into a vacuum chamber of glass and fused
to the inner walls of the chamber; and if the X-ray electrodes were let
into the glass chamber and a proper vacuum was attained, you could get a
fluorescent lamp of several candle-power. I started in to make a number
of these lamps, but I soon found that the X-ray had affected poisonously
my assistant, Mr. Dally, so that his hair came out and his flesh
commenced to ulcerate. I then concluded it would not do, and that it
would not be a very popular kind of light; so I dropped it.

"At the time I selected tungstate of calcium because it was
so fluorescent, I set four men to making all kinds of chemical
combinations, and thus collected upward of 8000 different crystals of
various chemical combinations, discovering several hundred different
substances which would fluoresce to the X-ray. So far little had come
of X-ray work, but it added another letter to the scientific alphabet.
I don't know any thing about radium, and I have lots of company." The
Electrical Engineer of June 3, 1896, contains a photograph of Mr. Edison
taken by the light of one of his fluorescent lamps. The same journal
in its issue of April 1, 1896, shows an Edison fluoroscope in use by
an observer, in the now familiar and universal form somewhat like a
stereoscope. This apparatus as invented by Edison consists of a flaring
box, curved at one end to fit closely over the forehead and eyes, while
the other end of the box is closed by a paste-board cover. On the inside
of this is spread a layer of tungstate of calcium. By placing the
object to be observed, such as the hand, between the vacuum-tube and
the fluorescent screen, the "shadow" is formed on the screen and can be
observed at leisure. The apparatus has proved invaluable in surgery and
has become an accepted part of the equipment of modern surgery. In 1896,
at the Electrical Exhibition in the Grand Central Palace, New York City,
given under the auspices of the National Electric Light Association,
thousands and thousands of persons with the use of this apparatus in
Edison's personal exhibit were enabled to see their own bones; and the
resultant public sensation was great. Mr. Mallory tells a characteristic
story of Edison's own share in the memorable exhibit: "The exhibit
was announced for opening on Monday. On the preceding Friday all the
apparatus, whi