t victory in the matter of
time and cost alone, besides which, the photo-telegraphic apparatus would
be merely an accessory to the already existing wireless installation.

[Illustration: FIG. 2.]

There have been numerous suggestions put forward for the wireless
transmission of photographs, but they are all more or less impracticable.
One of the earliest systems was devised by de' Bernochi of Turin, but his
system can only be regarded interesting from an historical point of view,
and as in all probability it could only have been made to work over a
distance of a few hundred yards it is of no practical value. Fig. 2 will
help to explain the apparatus. A glass cylinder A' is fastened at one end
to a threaded steel shaft, which runs in two bearings, one bearing having
an internal thread corresponding with that on the {8} shaft. Round the
cylinder is wrapped a transparent film upon which a photograph has been
taken and developed. Light from a powerful electric lamp L, is focussed by
means of the lens, N, to a point upon the photographic film. As the
cylinder is revolved by means of a suitable motor, it travels upwards
simultaneously by reason of the threaded shaft and bearing, so that the
spot of light traces a complete spiral over the surface of the film. The
light, on passing through the film (the transmission of which varies in
intensity according to the density of that portion of the photograph
through which it is passing), is refracted by the prism P on to the
selenium cell S which is in series with a battery B and the primary X of a
form of induction coil. As light of different intensities falls upon the
selenium cell,[2] the resistance of which alters in proportion, current is
induced in the secondary Y of the coil and influences the light of an arc
lamp of whose circuit it is shunted. This arc lamp T is placed at the focus
of a parabolic reflector R, from which the light is reflected in a parallel
beam to the receiving station.

The receiver consists of a similar reflector R' with a selenium cell E
placed at its focus, whose resistance is altered by the varying light
falling upon it from the reflector R. The selenium cell {9} E is in series
with a battery F and the mirror galvanometer H. Light falls from a lamp D
and is reflected by the mirror of the galvanometer on to a graduated
aperture J and focussed by means of the aplanatic lens U upon the receiving
drum A^2, which carries a sensitised photographic film. The