852 Mr. T. Thome Baker [April 22, 



island is seen represented and a lighthouse — or it might be a fort — 

 and by means of letters the positions of sections of an army on the 

 island are supposed to be designated, while the shaded portion might 

 mean that the " enemy " is in that part of the island. Such plans as 

 these could be drawn direct in shellac ink on a slip of metallic foil, 

 placed upon a portable machine coupled to a portable mihtary wireless 

 set, and communicated from one section of an army to another. The 

 small portable machines I have already shown are used for the wireless 

 transmissions, and they possess the advantage that " tapping " of the 

 communications would be quite impossible. It is for this reason that 

 I think the method would be of such value for mihtary and naval 

 purposes : even supposing that anyone wishing to intercept a plan or 

 written message were to have an exactly similar instrument, with the 

 same dimensions, screw-threads and so on, by merely altering the rate 

 of running by 5 or 10 per cent., according to prearranged signals, the 

 picture as received by the intercepting party would be quite unin- 

 telligible and confused. 



We have already seen that in the telegraphy of a picture by any 

 system accurate synchronising of the sending and receiving apparatus 

 is essential. Where a metallic circuit links the transmitting and 

 receiving instruments together the matter is an easy one, and we have 

 seen in what way it is effected. But when dealing with wireless work 

 the question of synchronism becomes more serious. I have employed 

 two methods, each of which appears to answer satisfactorily, and as 

 they are very important I will devote a few moments to their descrip- 

 tion. 



The first method secures accurate synchronism independently of 

 any wireless communication. You have already seen how in the ordi- 

 nary telegraphic work the receiving cylinder is driven rather faster 

 than the sending one, and when it finishes up a complete turn too 

 soon it is arrested until the sending cylinder has caught it up, when 

 the latter sends a reverse current which is responsible for its release. 

 But in the wireless apparatus both sending and receiving cylinders are 

 driven too fast, so to speak — that is, they are made to revolve in 4f 

 seconds instead of a nominal 5. A check comes into play at the end 

 of the revolution, and the cylinder is stopped until the 5 seconds are 

 completed, the motor working against a friction clutch in the ordinary 

 way during the stop. At the end of the fifth second each cylinder is 

 automatically released by chronometric means, in the manner shown 

 in the next diagram. [Lantern slide.] 



Here you will see that a special form of clock is used, with a 

 centre seconds hand which projects beyond the face by about an inch, 

 and to the end of it is attached a brush of exceedingly fine silver wires. 

 At every twelfth part of the circumference of the clock dial is fixed 

 a platinum pin, and consequently every five seconds the little brush 

 wipes against the convex surface of one of them. Each of these pins 

 is connected with one terminal of a battery B, the other side of the 



