1910] on the Telegraphy of Photographs^ Wireless and lij Wire. 847 



so as to show comparative times of exposure, and by its use radio- 

 graphic work can be greatly facilitated. 



It is interesting to note that the effect of the rays on the 

 fluorescent screen, as estimated by the selenium cell, differs less with 

 increasing distance, the further the anti-cathode is from it : — 



A good deal of time has, I am afraid, been taken up in giving 

 details of apparatus, but 1 will now show some of the results that 

 have been obtained in practice. The selenium machines already 

 referred to were operated between Paris, Manchester and London until 

 the end of the year 1908. The first photograph received [slide] was of 

 the King, and was received at the ' Daily Mirror ' installation in 

 November 1907. Several results will now be shown in the lantern, 

 and you will observe that they are all composed of parallel lines which 

 widen or "thin" according to the density of the picture. These 

 lines correspond to the movement of the shutter attached to the 

 strings of the Einthoven galvanometer, which regulates the thickness 

 of the spot of light focussed on the revolving sensitive film. This 

 spot of light traces a spiral line round the film, which, when developed, 

 is laid fiat, and the spiral becomes resolved into so many parallel lines. 



Late in 1908 Professor Korn introduced his telautograph, in 

 which a Caselli transmitter, such as already described for the telectro- 

 graph, is used, and a line sketch or half-tone photograph is attached 

 to the drum. The receiver is similar to that used in the selenium 

 machines, a spot of light cast on a revolving sensitive film being shut 

 off every time current flows through the wire of the galvanometer and 

 displaces it ; when displaced the shadow of the wire falls over a fine 

 slit placed in front of the film, and so prevents the light from passing 

 through to it. A line sketch transmitted from Paris to London in 

 this way is now shown. The methods of synchronising the sending 

 and receiving cylinders is the same as that used in the telectrograph, 

 but Professor Korn's work was done prior to mine, and his arrange- 

 ments were therefore copied by me. Similar methods have been 

 adopted for many years, however, in certain systems of ordinary tele- 

 graphy. 



There is a great deal of interesting matter connected with the 



Vol. XIX. (No. 104) 3 k 



