70 



Popular Science Monthly 



speech. It was the first time they had 

 ever been caught and recorded. Man 

 has been moldhig sound waves into 

 speech with his mouth and Hps along 

 lines represented by these curves for 

 thousands of years; but he didn't know 

 he was doing it. The chart on page 68 

 gives a complete set of these wave pat- 

 terns. Just how a man molds sound 

 waves into patterns such as these is 

 shown graphically on page 69, the word 

 "boat" serv'ing as an example. "Boat" 

 was chosen because its various letters, 

 as explained in the figure, make use in 

 succession of the lips, tongue, and 

 teeth — three of the principal agents in 

 shaping sounds. It is, therefore, a 

 representative example. 



Splitting Up a Spoken Word for 

 the Voice Typewriter 



Having discovered that a set of 

 natural letter-patterns exists, the next 

 thing is to make use of them. Accord- 

 ingly the machine shown on page 67 

 was designed, and has in part been 

 made to operate. It has been named 

 the "phonoscribe," and is intended to 

 write down speech in natural letter- 

 patterns automatically. As is described 

 in the figure, it makes use of a selenium 

 cell* and a set of special vibrating-mirror 

 mechanisms. These latter are each 

 arranged or "tuned," to care for vibra- 

 tions only of a certain magnitude. This 

 is necessary, for this machine is intended 

 to deal with spoken siicech instead of 

 whispers as did the recording machine 

 shown on page 66. Since spoken speech, 

 as has previously been outlined, is full 

 of troublesome extra tones which ob- 

 literate true wave forms, it becomes 

 imperative to have such tuned mechan- 

 isms as these to strain out the main or 

 fundamental wave from its incumbran- 

 ces. As shown in the figure on page 69 

 the main tone has a freciuency, or 

 vibration-rate, of 100 per second. The 

 incumbrances have rates respectively of 

 200 and 1,000 vibrations per second. 

 The three mirror-mechanisms which 

 li.indlc these rates are shown throwing 

 their united liglit-bi'ams on to the 

 selenium cell, iMilarging and diminisiiing 

 the wid th (jf this light beam in unison, 



•.S'lcnium iH .1 inrlal llic oliTtrtc:il rtindtictivity of which 

 varies (lircctly with Ihe amnnm ol liitlil falHiiK on it at 

 any itivon moment. 



and so cause the cell correspondingly to 

 vary the electric current through the 

 solenoid and recording apparatus shown 

 in the center of the figure. The width of 

 the light beams at any one instant of 

 course depends on how much the mirrors 

 happen to be vibrating, and this in 

 turn is controlled b\- the amount of 

 current coming from the telephone 

 transmitter at the right. The trans- 

 mitter naturally shapes this electric 

 current to correspond with the varying 

 sound waves reaching its diaphragm 

 from the speaker's lips. The whole 

 apparatus therefore works in harmony, 

 and a string of natural characters 

 appears on the paper, recording whatever 

 the speaker at the right has said — in 

 this case the word "boat." 



This phonoscribe is interesting mainly 

 as a forerunner of the actual voice- 

 operated typewriter itself. It embodies 

 some principles, notably that of the 

 selenium cell and accompanying vibra- 

 ting-mirror mechanisms, which will be 

 used in the ultimate speech-recording 

 machine itself. But in this latter case 

 of the typewriter, a whole collection of 

 selenium cells will be necessary — one for 

 each key on the machine. 



The selenium cells are so distributed 

 that only one letter of the alphabet can 

 affect them. Down inside the voice- 

 operated part of the machine these cells 

 will be erected to receive waves coming 

 from the vibrating mirrors when a person 

 speaks. The selenium cells within the 

 machine are arranged to correspond to 

 the characters of the natural alphabet 

 (see chart of these, page 68). If an 

 ordinary rotating mirror be placed in 

 the path of the light beams coming from 

 the vibrating mirrors, it will auto- 

 matically "spread out" these beams 

 from the straight line (such as is shown 

 on the selenium tx-ll of the figure on 

 page 67) to their natural wa\e shape 

 (that shown on page 68) — this on the 

 same principle that physics teachers of 

 old used to "spread out" sound vibra- 

 tions on a screen, using a revolving 

 mirror. The "spread-out" \ibrations 

 are intended to fall each on its own 

 selenimn cell in the base of the machine, 

 and because of this falling on the jiroper 

 selenium cell, to alTect the correspt)niling 

 t\ new ritcr ki'\'. 



