1910] on the Telegra'phy of PJwtographs, Wireless and hij Wire. 839 



closed by the stylus S2 and the metal drum) is a circuit containing 

 two batteries Bj and B2 and the two sections of a divided 1000 ohms 

 resistance, W^ and Wg. Shunted across the variable contacts of the 

 resistances is a variable condenser K. By varying the resistances W^ 

 and W2 we can vary the power of the current used to sweep out the 

 residuary charges in the line ; the current can, of course, flow through 

 the chemical paper on the drum, but the pole of the battery B^ con- 

 nected to the style is of opposite sign to that of the line unit connected 

 to it. 



When the leakance on the line is great and evenly distributed, 

 less reverse current from the balancer is necessary, this being quite 

 in accordance with Heaviside's formulae for telephony over lines with 

 capacity and inductance. It is interesting to note, also, that by in- 

 creasing the voltage of the reverse batteries B^ and B2, considerable 

 greater contrast can be obtained in the pictures ; the liner the half- 

 tone screen employed in splitting up the photographs into lines, the 

 higher, again, must the voltage of B^ and Bg be made. 



I should like to take up a few moments in referring to the actual 

 utihty of photo- telegraphy. The demand by the public for illustra- 

 tions in their daily papers must be admitted. News is telegraphed in 

 order to expedite its publication, and photographs illustrating this 

 news can therefore be telegraphed advantageously. But where a 

 large installation and establishment, with accumulators, a large instru- 

 ment and an operator to work it are required, the cost of telegraph- 

 ing every individual picture becomes quite out of proportion to its 

 value. It is therefore that I would call especial attention to the 

 portable instruments, the first one of which is shown for the first 

 time to-night. A photographer going to obtain pictures of some im- 

 portant function or interesting event can take the machine with him, 

 prepare his pictures and telegraph them to his head office, and when 

 the event is over he simply returns with the apparatus. For criminal 

 investigations the portable instrument will, I feel sure, become of 

 considerable value also. Through the continued courtesy shown by 

 the Postmaster-General and Major O'Meara, the Engineer-in-Chief, 

 we have been given every facility for developing the work, and I 

 believe that the uses of the portable instrument will before long have 

 been amply demonstrated. 



If a picture revolving beneath a tracer has to redraw itself, as it 

 were, on a piece of paper perhaps hundreds of miles away, it is 

 obvious that each mark redrawn must occupy a precisely similar spot 

 on the new paper as it does in the original picture. As cylinders or 

 drums are used in picture telegraphy, this means that they must 

 revolve in perfect unison. If one drum were to gain on the other 

 we should have, in the case of a portrait, a nose being recorded where 

 the eye ought to be, or something equally disastrous ; in fact, if the 

 two machines get the least bit out of step the received picture is com- 

 pletely ruined. The method of synchronising used by Professor 



