4o6 POPULAR SCIENCE MONTHLY 



bell box so that the battery circuit might be under the control of and 

 closed and opened by the telephone hook switch. Interior and sec- 

 tional views of the Blake transmitter are shown in Fig. 31. With 

 each of these early Blake instruments a circular was sent stating that it 



can be used only as a transmitter, and requires a telephone to hear with. This 

 is the most complete and perfect set of instruments that can be used for tele- 

 phonic communication. It will transmit the faintest whisper with perfect 

 distinctness. 



It is a fact that no modern transmitter exceeds the Blake in clearly 

 and distinctly reproducing the articulation of the subscriber. But 

 owing to the mechanism employed in its single contact form, it proved 

 deficient in volume or power required on noisy and on long suburban 

 lines. Again, its first cost was comparatively low, and the Blake and 

 similar types of transmitters possess the striking advantage over the 

 old hand telephone of being placed on a local circuit, thus removing 

 their varying resistances from the line circuit, to the improvement of 

 the qualities of transmission. The old hand telephone and the early 

 box magneto telephone formed a part of the main-line circuit, thus 

 materially increasing its resistance. 



The first Blake instruments were larger in whole and in part than 

 the transmitter so familiar to all telephone users, while the screw that 

 controlled the proper adjustment of the electrodes projected through 

 the box, thus making it possible for the subscriber to adjust the in- 

 strument for long circuits or short lines, regardless of the mood he 

 might be in. It only required a little experience to teach the local 

 companies that the wiser plan was to have trained telephone inspectors 

 do the necessary adjusting. So the adjusting screw was put insido 

 the box and the door fastened with lock and key. 



There is a wide difference between the underlying principles of 

 Bell's self-contained transmitter and his variable resistance trans- 

 mitter, both of which were exhibited at the Centennial. The micro- 

 phone, or carbon, or battery transmitter, now in use on nearly all tele- 

 phone lines, belongs to the variable resistance type. Unlike the early 

 hand transmitter, it does not generate current, but serves as a voice- 

 governed mechanical regulator of the flow of current chemically gen- 

 erated in a battery. 



After Graham Bell had shown how to solve the problem of speech 

 transmission, many other inventors were naturally quick to suggest 

 commercial improvements. A few worked hand-in-hand with Graham 

 Bell and gladly contributed to his success. Among this number was 

 Francis Blake, Jr., who invented the transmitter bearing his name 

 and which was the only transmitter used on a majority of the Bell 

 lines prior to 1893. Mr. Blake was a Christmas present in 1850; 

 graduated from the Brookline, Mass., High School in 1866; entered 



