DISCOVERY 



125 



In this instrument all the notes are sounded at 

 once, producing discord when a sheet of white paper 

 is laid on the table, and on the contrary there is dead 



III 



silence in the telephone when a piece of black paper 

 is substituted for the white. If the scala passes 

 over the letter V, for example, the top note (high 

 soh) will first be silenced, then me, ray, doh, ray, me, 

 and soh in succession. Such an instrument is there- 

 fore referred to as a " white sounding optophone," 

 for the reason already explained, that it is the white 

 spaces around the words which form the musical 

 motifs. The newest optophones have been so modified 

 by the introduction of the balancer bridge, of which 

 we have already spoken, so as to " sound black." 

 In this case white paper produces silence in the 



I480 



FIG. 6. 

 SCAI,.\ PASSING 0\'ER PRINTED LETTERS. 



telephone, and each black letter has its own musical 

 motif, which can be distinguished and learnt with 

 much greater ease by the blind reader, as they are 



far more characteristic than the motifs produced by 

 the white spaces surrounding the letters in the older 

 type of machine. With this instrument the letter V 

 is represented by the motif soh, me, ray, doh, ray, 

 me, soh. 



How the two selenium bridges are connected to the 

 battery and telephone is seen at a glance in Fig. 7, 

 and the working of the balancer is explained by the 

 makers in a booklet on the optophone, published by 

 them, from which I have quoted, and from which they 

 have kindly allowed me to reproduce the various 

 figures illustrating this article. " The balancer is 

 illuminated by a small part of the intermitted 

 light reflected aside before it reaches the paper, and 

 is so connected to the telephone and battery that 

 the current traversing the balancer bridge acts in the 

 reverse direction in the telephone to that of the 

 current through the main selenium bridge. The 



Main 



Selenium Brirtgo 



(Se. No. 1). 



Balancer 



Selenium Bridge 



tSe. No. 2j. 



\ . 



^ 



^ Battery of 

 :i: small dry cells, 

 ~\[ ^ about 80 volts. 



Telephone. ^=^ 



Fig. 7. 

 DI.\GR.\M OF SELENIUM BRIDGE CONNECTIONS. 



balancer thus tends to cause the telephone to sound 

 all the notes continuously, and the main selenium 

 bridge, that receives the light reflected from the 

 paper, annuls the effect on the telephone in respect 

 to any note when the spot of light corresponding to 

 that note falls on white paper. The division of the 

 total voltage of the battery can be varied, so that 

 when the whole scala falls on white paper, the telephone 

 is silent, and notes are sounded only as the scala moves 

 over the black letters." 



One of the finished instruments was shown at the 

 Scientific Products E.xhibition at the Caxton Hall in 

 the summer of 1919, and since then the optophone has 

 become quite a feature of all exhibitions where British 

 post-war industry is to be seen. It seems a fitting 

 atonement that a firm which formerly devoted itself 

 to instruments of precision for use in warfare (the 

 range-finder, for example), should make an effort to 



