to
issue in spray. As the paper moves over the pulleys a delicate hair line
is marked, straight when the siphon is stationary, but curved when the
siphon is pulled from side to side by the oscillations of the signal
coil.

It is to the mouse-mill that me must look both for the electricity which
is used to electrify the ink and for the motive power which drives
the paper. This unique and interesting little motor owes its somewhat
epigrammatic title to the resemblance of the drum to one of those
sparred wheels turned by white mice, and to the amusing fact of its
capacity for performing work having been originally computed in terms of
a 'mouse-power.' The mill is turned by a stream of electricity flowing
from the battery above described, and is, in fact, an electro-magnetic
engine worked by the current.

The alphabet of signals employed is the 'Morse code,' so generally
in vogue throughout the world. In the Morse code the letters of the
alphabet are represented by combinations of two distinct elementary
signals, technically called 'dots' and 'dashes,' from the fact that the
Morse recorder actually marks the message in long and short lines,
or dots and dashes. In the siphon recorder script dots and dashes are
represented by curves of opposite flexure. The condensers are merely
used to sharpen the action of the current, and render the signals more
concise and distinct on long cables. On short cables, say under three
hundred miles long, they are rarely, if ever, used.

The speed of signalling by the siphon recorder is of course regulated by
the length of cable through which it is worked. The instrument itself
is capable of a wide range of speed. The best operators cannot send over
thirty-five words per minute by hand, but a hundred and twenty words
or more per minute can be transmitted by an automatic sender, and the
recorder has been found on land lines and short cables to write off the
message at this incredible speed. When we consider that every word
is, on the average, composed of fifteen separate waves, we may better
appreciate the rapidity with which the siphon can move. On an ordinary
cable of about a thousand miles long, the working speed is about twenty
words per minute. On the French Atlantic it is usually about thirteen,
although as many as seventeen have sometimes been sent.

The 'duplex' system, or method of telegraphing in opposite directions
at once through the same wire, has of late years been applied, in