the two machines so that transmission and reception begin simultaneously; (4) the correct regulation of the speed of the driving motors; (5) the simplicity and reliability of the entire arrangement. Points 1 and 2 are dependent upon several factors; the number of contacts made by the stylus per minute; the size of the metal print used; the number of lines per inch 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.
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
the drum has traversed the required distance, the end of the shaft pushes back the spring M, breaking the circuit of the driving gear and stopping the machine. The machine is connected to the driving gear by the flexible coupling A.
M, motor; Y, isochroniser; F, clutch; A, machine; R, stylus; S, relay; X, gearing; O, circuit breaker; T, receiver; C, condenser; U, telephone relay; K, polarised relay; L, contact breaker; D, D1, D2, D3, batteries; P, friction brake; B, B1, double-pole two-way switches; N, N1, N2, single switches; W, key; E, electric clock; J, telephones.