nch on the screen
used in preparing the print; and the accurate and harmonious working of the
various pieces of apparatus employed.

In the system under discussion the size of the metal print used is 5 inches
by 7 inches, and a screen having 50 lines to the inch is used for preparing
it. With the drum of the machine making one revolution in four seconds, the
stylus makes 87 contacts per second, or 5220 a minute, the time for
complete transmission being twenty-five minutes. By the use of ordinary
relays not more than 2000 contacts a minute can be obtained, and in the
present system it is only by means of a specially designed relay that such
a high rate of working has been made possible. Similarly, too, with the
receiving of such a large number of signals transmitted at such a high
speed, a special instrument has been devised that can record this number of
signals without any trouble, and could even record up to 8000 signals a
minute, provided that a suitable transmitter could be designed. {76}

In the present system the writer does not claim to have completely solved
the problem of the wireless transmission of photographs, but it is a great
advance on any system previously described, and the following advantages
are put forward for recognition: (1) a greatly improved method of
transmitting and receiving; (2) a simple method of regulating the speed of
the driving motors and maintaining isochronism with a limit of error of
less than 1 in 800; (3) an arrangement for synchronising the two machines
whereby transmitting and receiving begin simultaneously; (4) the use of one
machine only at each station.

TRANSMITTING APPARATUS

A diagrammatic representation of the apparatus required for a complete
station, transmitting and receiving combined, is given in Fig. 35, the
usual wireless equipment having been omitted from the diagram to avoid
confusion.

_The Machine._--This, as will be seen from Fig. 36, consists of a
base-plate M, to which are attached the two bearings B and B'. The bearing
B' is fitted with an internal thread to correspond with the threaded
portion of the shaft D. The drum V is a brass casting, being fastened to
the shaft by set screws. The shaft is threaded 75 to the inch. The bearings
are preferably of the concentric type. The circuit breaker C is so arranged
that when {77} the drum has traversed the required distance, the end of the
shaft pushes back the spring M, breaking the circuit of the driving gear