a pinch of dust that it becomes a free avenue
instead of a barricade. Through that avenue a powerful blow from a local
store of energy makes itself heard and felt. No device of the trigger
class is comparable with this in delicacy. An instant after a signal has
taken its way through the coherer a small hammer strikes the tiny tube,
jarring its particles asunder, so that they resume their normal state of
high resistance. We may well be astonished at the sensitiveness of the
metallic filings to an electric wave originating many miles away, but
let us remember how clearly the eye can see a bright lamp at the same
distance as it sheds a sister beam. Thus far no substance has been
discovered with a mechanical responsiveness to so feeble a ray of light;
in the world of nature and art the coherer stands alone. The electric
waves employed by Marconi are about four feet long, or have a frequency
of about 250,000,000 per second. Such undulations pass readily through
brick or stone walls, through common roofs and floors--indeed, through
all substances which are non-conductive to electric waves of ordinary
length. Were the energy of a Marconi sending-instrument applied to an
arc-lamp, it would generate a beam of a thousand candle-power. We have
thus a means of comparing the sensitiveness of the retina to light with
the responsiveness of the Marconi coherer to electric waves, after both
radiations have undergone a journey of miles.

An essential feature of this method of etheric telegraphy, due to
Marconi himself, is the suspension of a perpendicular wire at each
terminus, its length twenty feet for stations a mile apart, forty feet
for four miles, and so on, the telegraphic distance increasing as the
square of the length of suspended wire. In the Kingstown regatta, July,
1898, Marconi sent from a yacht under full steam a report to the shore
without the loss of a moment from start to finish. This feat was
repeated during the protracted contest between the _Columbia_ and the
_Shamrock_ yachts in New York Bay, October, 1899. On March 28, 1899,
Marconi signals put Wimereux, two miles north of Boulogne, in
communication with the South Foreland Lighthouse, thirty-two miles
off.[4] In August, 1899, during the manoeuvres of the British navy,
similar messages were sent as far as eighty miles. It was clearly
demonstrated that a new power had been placed in the hands of a naval
commander. "A touch on a button in a flagship is all that is now n