m the telephone, and I found that the moment I
touched with the toe of my boot a blade of grass or the petal of a daisy
the sound was again audible.

The question will naturally arise, Through what length of wire can the
telephone be used? In reply to this I may say that the maximum amount of
resistance through which the undulatory current will pass, and yet
retain sufficient force to produce an audible sound at the distant end,
has yet to be determined; no difficulty has, however, been experienced
in laboratory experiments in conversing through a resistance of 60,000
ohms, which has been the maximum at my disposal. On one occasion, not
having a rheostat [for producing resistance] at hand, I passed the
current through the bodies of sixteen persons, who stood hand in hand.
The longest length of real telegraph line through which I have attempted
to converse has been about 250 miles. On this occasion no difficulty was
experienced so long as parallel lines were not in operation. Sunday was
chosen as the day on which it was probable other circuits would be at
rest. Conversation was carried on between myself, in New York, and Mr.
Thomas A. Watson, in Boston, until the opening of business upon the
other wires. When this happened the vocal sounds were very much
diminished, but still audible. It seemed, indeed, like talking through a
storm. Conversation, though possible, could be carried on with
difficulty, owing to the distracting nature of the interfering currents.

I am informed by my friend Mr. Preece that conversation has been
successfully carried on through a submarine cable, sixty miles in
length, extending from Dartmouth to the Island of Guernsey, by means of
hand telephones.

PHOTOGRAPHING THE UNSEEN: THE ROENTGEN RAY

H. J. W. DAM

[By permission from _McClure's Magazine_, April, 1896, copyright by
S. S. McClure, Limited.]

In all the history of scientific discovery there has never been,
perhaps, so general, rapid, and dramatic an effect wrought on the
scientific centres of Europe as has followed, in the past four weeks,
upon an announcement made to the Wuerzburg Physico-Medical Society, at
their December [1895] meeting, by Professor William Konrad Roentgen,
professor of physics at the Royal University of Wuerzburg. The first news
which reached London was by telegraph from Vienna to the effect that a
Professor Roentgen, until then the possessor of only a local fame in the
town mentioned, had di