T. Hancock, D. E. Hughes, W. Sturgeon 191 



seven years old. He was connected for a time with a college 

 in Kentucky, first as Professor of Music and then as a 

 teacher of Natural Philosophy, but gave up the academic 

 career, at the age of twenty-three, to supervise the manu- 

 facture of the type-printing machine which he had invented. 

 Everyone is now familiar with that perfect little instrument 

 which distributes typed messages simultaneously all over a 

 city. The income which the inventor derived from it gave 

 him the desired leisure for further scientific investigations. 

 His most important discovery is that of the microphone, in 

 which two pieces of carbon are in loose contact, making 

 an electric connexion that is exceedingly sensitive to the 

 slightest disturbance caused by a wave of sound or an 

 electric impulse. The carbon contact was soon introduced 

 into telephone transmitters, and helped much to make tele- 

 phones serviceable for ordinary use. In observing the effect 

 of electric impulses in carbon contacts Hughes anticipated 

 the invention of the " coherer," which made the trans- 

 mission of wireless electric messages to great distances 

 possible. It is, indeed, related that, so far back as 1879, 

 Hughes could detect by the microphone " electric impulses " 

 at a distance of 500 yards. 1 The researches on the microphone 

 and on another useful instrument, the " induction balance," 

 were carried out in England, where Hughes spent the later 

 part of his life. 



All industrial applications of electricity are based on 

 Faraday's discoveries, and Sturgeon's invention of the electro- 

 magnet. After it had been shown experimentally by the 

 former that an electric current is produced when a wire is 

 moved in a magnetic field, it was pretty obvious that appliances 

 could be constructed for generating currents by mechanical 

 means. There is no indication that at first anyone was aiming 

 at currents of great intensity; machines were constructed 

 partly on account of their scientific interest and partly to 

 be used for purposes of telegraphy. Sturgeon was the first to 

 attack the inverse problem of using a current to do mecha- 

 nical work, and it has been described in our first chapter 

 how Joule started his work by trying to improve the 



1 " Encyclopaedia Britannica." 



