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Via. 2. Fig. 3. 



DIAGRAJKtVTIC ARRANGEMEXT OF OPTOPHONE. 



be obtained. These are, of course, well-known facts. 

 It is the role played by the selenium which is the novel 

 feature. 



In the optophone a selenium bridge is exposed to 

 successions of sets of light pulsations, which vary ac- 

 cording to the forms of letters as these are passed over 

 in traversing a line of printed type, each letter being 

 indicated in the telephone by a characteristic motif 

 comprising successions of single notes and chords. And 

 the letters of this sound alphabet can be readily 

 learned. 



The optophone is quite small, not much bigger 

 than a portable type\vriter, and externally (Fig. i) 

 there is not much to be seen, just a glass table on 

 which the book or other printed matter rests face 

 downwards. To understand the mechanism of the 

 machine, the reader must glance at the diagrammatic 

 views of the mysteries hidden away under this table. 

 Each letter is illumined in turn by the light which is 

 thrown up from beneath, and which is made to travel 

 along the lines of print by a specially designed variable 

 speed governor. The source of light is a small straight 

 electric filament lamp (Figs. 2 and 3), the rays of which 

 are made to pass through a diaphragm on to a per- 

 forated disc (Fig. 4), which is caused to rotate rapidly 

 by means of a small magneto-electric motor driven 

 from secondary cells. The light which passes through 

 this disc is directed by suitable lenses on to the printed 

 page, and traverses an aperture in the selenium tablet 

 which is placed directly under the glass table. As 

 this tablet travels along with the rest of the optical 

 apparatus to which it is attached, it catches the light 

 diffusely reflected from the white paper surrounding 

 each letter in turn. This the makers call the " main 



selenium bridge," to distinguish it from the 

 " balancer bridge." the object of which will 

 shortly be explained. Both these bridges 

 are shown in their various stages of pro- 

 duction in Fig. 5. The graphite areas are 

 simply pencilled on, leaving the " lane " of 

 bare porcelain between. The tablet, or 

 bridge, is afterwards smeared with selenium 

 paste and annealed. The actual working 

 principle of the instrument is as simple as 

 it is ingenious : the light which passes the 

 live rings of perforations in the rotating 

 disc falls on the printed matter as five dots 

 in a row, and is known as the "scala" 

 (Fig. 6). Each spot pulsates at a rate 

 corresponding to the number of the per- 

 forations in the particular circle to which 

 it belongs, multiplied by the number of 

 revolutions of the disc per second. The 

 circles are provided with 18, 24, 27, 30, 

 and 36 holes respectively, from the centre 

 The pulsations of each spot of light 

 are translated into a definite musical note in the 

 telephone attached, the pitch of the note var^'ing 

 according to the speed at which the disc is rotating, 

 but the intervals, which are those between the notes 

 G, C, D', E', G' (soh, doh, ray, me, soh), remain 

 the same, whatever this speed may be. There is a 

 focusing arrangement which adjusts the width of the 

 scala to the size of the print, so that as the scala 

 passes over the type, combinations of the musical 

 notes are given out, forming a motif which is peculiar 

 to each letter, and which can be heard in the tele- 

 phone connected with the main selenium bridge as 

 mentioned above. 



outwards. 



ROT.\TIXG DISC 



