lar
galvanometer, G', to earth. The needle of G' is also connected to the
pen, P, by a taut thread, t', stretched by means of the spring, s.
Now, since the needle of each of these galvanometers deflects in
proportion to the strength of the current flowing through its coil,
the points of these two needles keep moving with the varying currents.
But since these currents vary the motions of the sending pen, the
receiving pen controlled by the united movements of the needles will
trace out a close copy of the original writing. We give on another
page a facsimile of a sentence written by Mr. Cowper's telegraph.

[Illustration: THE COWPER WRITING TELEGRAPH.]

The receiving pen is a fine glass siphon, drawing off aniline ink from
a small glass holder. There are thirty-two coils, C, in each circuit,
with a corresponding number of contact plates, c, so as to get
accuracy of working. A few Daniell's cells are sufficient to operate
the apparatus, and writing has been already sent successfully over a
line 40 miles in length. The writing may be received either of the
same size or larger or smaller than the original, as the case may be.
At present the writing must not be too hurried, that is, unless the
characters are bold and well formed; but further improvement will, of
course, quicken the working of the apparatus.

The engravings, Figs. 1 to 4, illustrate the actual apparatus. Fig. 4
is a plan of the sending instrument, with the writing pencil, a, the
traveling paper, b, the light connecting rods or arms, d (which
correspond to a in the theoretical diagram above), the series of metal
contact plates over which these arms slide, the resistance coils
connected to these plates, and the battery and line wires. It will be
seen that each arm, d, is connected to its particular battery, and
each set of contact plates to its particular line. Fig. 3 is an
elevation of the sending instrument, in which a is the pencil as
before, c c the contact plates over which the arms, d d, slide, f f
the coils, and b the traveling slip of paper.

Fig. 2 is a plan of the receiving instrument, in which h h are the
light pivoted needles surrounded by coils of fine insulated copper
wires, i i, and controlled in their zero position by the
electro-magnets, j j j j, placed underneath, the whole forming a pair
of galvanoscopes or current detecters, one for each line. It will be
understood that the varying currents from the lines are allowed to
flow through the