1881.] on Selenium and its apjiUcations to the Photophone^ dc. 535 



a photographic lens L. Tlio liolc II in the cylinder is then brought 

 to the brightest point of tlie focussed picture, and a scrap of sensitised 

 paper being placed under the jilatiuum point of the receiver, tho 

 variable resistance is adjusted so that tlic two opposite currents 

 through the paper neutralise each other. When this is accomplished 

 the two cylinders are screwed back as far as they will go, tho 

 cylinder of the receiver is covered with sensitised paper, and all is 

 ready to commence operations. 



The two cylinders are caused to rotate slowly and synchronously. 

 The little hole in the transmitting cylinder will in the course of its 

 spiral path cover successively every point of the focussed picture, and 

 the amount of light falling at any moment upon the selenium cell 

 will be proi^ortional to the illumination of that particular spot of 

 tho picture which, for the time being, is occupied by the pin-hole. 

 During the greater part of each revolution the platinum point will 

 trace a uniform brown line uj)on the prepared paper, but when the 

 pin-hole happens to be passing over a bright part of the picture, this 

 line is enfeebled or broken. The spiral traced by the point is so 

 close as to produce, at a little distance, the appearance of a uniformly 

 coloured surface, and the breaks in the continuity of the line constitute 

 a picture which, if the instrument were perfect, would be a counter- 

 part of that projected upon the transmitter. 



The pictures upon which I have hitherto operated have been 

 mostly simple designs, such as diamonds and squares cut out of thin 

 metal, and projected by a magic lantern (see Fig. 4). But the instru- 

 ment is in its earliest stage of infancy. It is at present hardly a 



Fig. 4. 



Image Fucussed upon Transmitter. Image as Reproduced by Eeceiver. 



single month old, and I regret to say that since its birth it has been 

 shamefully neglected, circumstances having prevented me from giving 

 it even the ordinary care and attention which all young creatures 

 ought to receive. Nevertheless, I cannot but think that it is capable 

 of indefinite development; and should there ever bo a demand 

 for telephotography, it may in time turn out to bo a useful membei' 

 of society. 



