NA TURE 



57 



THURSDAY, MAY i6, 1878 



THE MICROPHONE 



WE -were enabled to announce a fortnight ago, that 

 Prof. Hughes, the inventor of the type-printing 

 telegraphic apparatus which goes by his name, has made 

 the wonderful discovery that certain bodies are sensitive 

 to sound, in the same way as selenium is sensitive to 

 light. That is to say, if we place these bodies in the 

 circuit of a small battery, and subject them to sound- 

 vibrations, in other words, talk at them, the electric 

 current continually passing through it will be so con- 

 tinuously modified by the voice that the object may be 

 used instead of a telephone for sending a message. 



Since our note was penned an opportunity has been 

 afforded us by the kindness of Prof. Hughes, of inquiring 

 into the precise manner in which this and other startling 

 results have been accomplished. 



The impression left upon us by a careful following of 

 all Mr. Hughes's experiments, is, that by them Ave are 

 brought face to face with one of the most wonderful 

 discoveries of the century. To see Prof. Huxley, who 

 was one of those present, solemnly talking at a small 

 glass tube about two inches long, was, in itself, a sight 

 worth seeing ; but to go into another part of the house, and, 

 on putting a telephone to the ear to find that the talking 

 at the glass tube there resulted in a quite perfect, very 

 easily audible reproduction of the quality of every word 

 which the Professor uttered, was a thing almost transcend- 

 ing the marvellous. 



That by such experiments as these we are beginning to 

 tap sources and modes of energy hitherto undreamt of 

 was rendered most evident by an experiment which has 

 suggested the name, placed at the head of this article, 

 for the instrument by which it is accomplished. The 

 delicate rubbing of a fine camel's hair pencil over a 

 smooth wooden surface under certain conditions of con- 

 tact, although, of course, inaudible in the ordinary way, 

 was rendered evident in the telephone by a crackling 

 noise, of which the intensity was almost painful to the 

 ear. In this way Mr. Hughes has enabled Mr. Preece to 

 hear a fly walk ; we were not so fortunate as to hear this, 

 because the only small fly available in the room, after 

 having been carefully hunted down and inclosed in a 

 small tumbler, obstinately declined to walk on the wood. 



We have said so much by way of giving an idea in the 

 first instance of the manner and result of the experi- 

 mentation. The kind of inquiry into the molecular struc- 

 ture of bodies it renders possible, and the applications to 

 which, undoubtedly, it will soon be put, will be best 

 grasped after a somewhat detailed description of the 

 apparatus itself. This description was given by Mr. 

 Hughes at the meeting of the Royal Society held on 

 Thursday last, and it may safely be said that never was a 

 more difficult problem presented to men of science by 

 simpler apparatus. 



Although a telephone, as Avill be seen, is part of the 

 apparatus utilised, the total problem presented by Mr. 

 Hughes is a very much more complex one than that pre- 

 sented by that most marvellous of modern instruments. 



Mr. Hughes has employed the telephone as a phono- 



VOL. XVIII. — No. 446 



scope of the greatest delicacy, to detect variations in 

 currents, and the consequent reproduction of sound. 

 The materials experimented upon by him were arranged 

 as in the following sketch, in which B represents a 

 battery, S the source of sound or material examined, and 

 T the telephone or phonoscope. -^ 



Fig. I. 



The battery was a simple Daniell' s cell, of Minotto's 

 form, made by using three common tumblers, a spiral 

 piece of copper wire being placed at the bottom of each 

 glass and covered with sulphate of copper, and the glass 

 being then filled with well-moistened clay and water. A 

 piece of zinc as the positive element was placed upon the 

 clay. Insulated wires were attached to each plate, and 

 three of these cells were joined in series. 



All experiments were made on a closed circuit. ; , 



Prof. Hughes's work was begun by studying the effect of 

 strains. Sir W. Thomson and others having shown that 

 the resistance offered by wires to currents is affected by 

 them, it followed that as the conveyance of sound 

 vibrations must induce variations in strains, the wire 

 resistance should vary when it was used to convey sound. 



A stretched wire was therefore, in the first instance, 

 introduced at S. The wire was talked at, but no effect 

 was marked until a breaking strain was applied ; at the 

 moment of breaking, a sound was heard. Next, the 

 broken ends were pressed together. The next stage in 

 the experiments we quote from the paper itself : — 



" It was soon found that it was not at all necessary to 

 join two wires endwise together to reproduce sound, but 

 that any portion of an electric conductor would do so 

 even when fastened to a board or to a table, and no matter 

 how complicated the structure upon this board, or the 

 materials used as a conductor, provided one or more por- 

 tions of the electrical conductor were separated and only 

 brought into contact by a slight but constant pressure. 

 Thus, if the ends of the wire terminate in two common 

 nails laid side by side, and are separated from each other 

 by a slight space, were electrically connected by laying a 

 similar nail between them, sound could be reproduced. 

 The effect was improved by building up the nails log-hut 

 fashion, into a square configuration, using ten or twenty 

 nails. A piece of steel watch-chain acted well. Up to 

 this point the sound or grosser vibrations were alone pro- 

 duced, the finer inflections were missing, or, in other 

 words, the timbre of the voice was wanting, but in the 

 following experiments the timbre became more and more 

 perfect until it reached a perfection leaving nothing to be 

 desired. I found that a metallic powder such as the 

 white powder — a mixture of zinc and tin — sold in com- 

 merce as "white bronze," and fine metallic filings, intro- 

 duced at the points of contact, greatly added to the 

 perfection of the result." 



Here, then, was articulate speech clearly reproduced. 



Prof. Hughes's next efforts were to discover the best 

 material and form to give to his apparatus. 



" Although I tried all forms of pressure and modes of 

 contact, a lever, a spring, pressure in a glass tube sealed 



