electric circuit as often as two thousand times a
second. The means for this amazing performance are simplicity itself
(Fig. 74). A jar, _a_, containing a solution of sulphuric acid has two
electrodes immersed in it; one of them is a lead plate of large surface,
_b_; the other is a small platinum wire which protrudes from a glass
tube, _d_. A current passing through the cell between the two metals at
_c_ is interrupted, in ordinary cases five hundred times a second, and
in extreme cases four times as often, by bubbles of gas given off from
the wire instant by instant.

FOOTNOTES:

[3] "History of the Wireless Telegraph," by J. J. Fahie. Edinburgh and
London, William Blackwood & Sons; New York, Dodd, Mead & Co., 1899. This
work is full of interesting detail, well illustrated.

[4] The value of wireless telegraphy in relation to disasters at sea was
proved in a remarkable way yesterday morning. While the Channel was
enveloped in a dense fog, which had lasted throughout the greater part
of the night, the East Goodwin Lightship had a very narrow escape from
sinking at her moorings by being run into by the steamship _R. F.
Matthews_, 1,964 tons gross burden, of London, outward bound from the
Thames. The East Goodwin Lightship is one of four such vessels marking
the Goodwin Sands, and, curiously enough, it happens to be the one ship
which has been fitted out with Signor Marconi's installation for
wireless telegraphy. The vessel was moored about twelve miles to the
northeast of the South Foreland Lighthouse (where there is another
wireless-telegraphy installation), and she is about ten miles from the
shore, being directly opposite Deal. The information regarding the
collision was at once communicated by wireless telegraphy from the
disabled lightship to the South Foreland Lighthouse, where Mr. Bullock,
assistant to Signor Marconi, received the following message: "We have
just been run into by the steamer _R. F. Matthews_ of London. Steamship
is standing by us. Our bows very badly damaged." Mr. Bullock immediately
forwarded this information to the Trinity House authorities at
Ramsgate.--_Times_, April 29, 1899.

ELECTRICITY, WHAT ITS MASTERY MEANS: WITH A REVIEW AND A PROSPECT

GEORGE ILES

[From "Flame, Electricity and the Camera," copyright by Doubleday,
Page & Co., New York.]

With the mastery of electricity man enters upon his first real
sovereignty of nature. As we hear the whirr of the dynamo o