Nov. 15, 1877] 



NATURE 



49 



are not due wholly to sudden changes in the magnetic con- 

 dition of the iron core, as heretofore supposed, but that a 

 portion of the effect results from vibrations in the insulated 

 copper wires composing the coils. An electro-magnet 

 was arranged upon circuit unto an instrument for inter- 

 rupting the current, the rheotome being placed in a 

 distant room so as to avoid interference with the experi- 

 ment. Upon applying the ear to the magnet a musical 

 note was clearly perceived, and the sound continued after 

 the iron core had been removed from the coils. The effect 

 may probably be explained by the attraction of the coils for 

 one another during the passage of the galvanic current 

 and the sudden cessation of such attraction when the 

 current ceased. It is probable, too, that a molecular 

 vibration is occasioned in the conducting wire by the 

 passage of an intermittent current. I have found that 

 very distinct sounds proceed from straight pieces of iron, 

 steel retort-carbon, and plumbago, when an intermittent 

 current is passed through them." 



When a powerful current is passed through the body a 

 musical note can be perceived when the ear is closely 

 applied to the arm of the person experimented upon. 

 The sound seems to proceed from the muscles of the fore- 

 arm and from the biceps muscle. Mr. Elisha Gray has 

 also produced audible effects by the passage of electricity 

 through the human body. An extremely loud musical 

 note is occasioned by the spark of a Ruhmkorff's coil 

 when the primary circuit is made and broken with suffi- 

 cient rapidity ; when two rheotomes of different pitch are 

 caused simultaneously to open and close the primary 

 circuit a double tone proceeds from the spark. 



A curious discovery has been made by Prof, Blake. 

 He constructed a telephone in which a rod of soft iron, 

 about six feet in length, was used instead of a permanent 

 magnet. A friend sang a continuous musical tone into 

 the mouth-piece of a telephone, which was connected 

 with the sofc iron instrument alluded to above. It was 

 found that the loudness of the sound produced In this 

 telephone varied with the direction in which the iron rod 

 was held, and that the maximum effect was produced 

 when the rod was in the position of the dipping needle. 



This curious discovery of Prof. Blake has been verified 

 by Prof. Bell. 



" Prof. Peirce has observed the most 'curious sounds 

 produced from a telephone in connection with a tele- 

 graph-wire during the aurora borealis ; and I have just 

 heard of a curious phenomenon lately observed by Dr. 

 Channing. In the City of Providence, Rhode Island, 

 there is an over-house wire about one mile in extent with 

 a telephone at either end. On one occasion the sound of 

 music and singing was faintly audible upon one of the 

 telephones. It seemed as if some one were practising 

 vocal music with a pianoforte accompaniment. The 

 natural supposition was that experiments were being 

 made with the telephone at the other end of the circuit, 

 but upon inquiry this proved not to have been the case. 

 Attention having thus been directed to the phenomenon, 

 a watch was kept upon the instruments, and upon several 

 subsequent occasions the same fact was observed at both 

 ends of the line by Dr. Channing ar.d his friends. It was 

 proved that the sounds continued for about two hours, 

 and usually commenced about the same time. A searching 

 examination of the line disclosed nothing abnormal in its 

 condition, and I am unable to give you any explanation 

 of this curious phenomenon. Dr. Channing has, how- 

 ever, addressed a letter upon the subject to the editor of 

 one of the Providence papers, giving the names of such 

 songs as were recognised, with full details of the 

 observations, in the hope that publicity may lead to the 

 discovery of the^ performer, and thus afford a solution of 

 the mystery." 



Prof. Bell referred to some experiments made by Mr. F. 

 A. Gower and himself to show the slight earth connection 

 required to establish a circuit for the telephone. 



" One experiment which we made is so very interesting 

 that I must speak of it in detail. Mr. Gower made earth 

 connection at his end of the line by standing upon a grass 

 plot, whilst at the other end of the line I stood upon a 

 wooden board. I requested Mr. Gower to sing a con- 

 tinuous musical note, and to my surprise the sound was 

 very distinctly audible from the telephone in my hand. 

 Upon examining my feet I discovered that a single blade 

 of grass was bent over the edge of the board, and that my 

 foot touched it. The removal of this blade of grass was 

 followed by the cessation of the sound from the telephone, 

 and I found that the moment I touched with the toe of 

 my boot a blade of grass or the petal of a daisy, the sound 

 was again audible." 



Prof. Bell concluded as follows : — " The question will 

 naturally arise, through what length of wire can the 

 telephone be used .'' In reply to this I may say that the 

 maximum amount of resistance through which the undu- 

 latory current will pass, and yet retain sufficient force to 

 produce an audible sound at the disturbed end, has yet 

 to be determined ; no difficulty has, however, been expe- 

 rienced in laboratory experiments in conversing through 

 a resistance of 60,000 ohms, which has been the maximum 

 at my disposal. On one occasion, not having a rheostat 

 at hand, I may mention having passed the current through 

 the bodies of sixteen persons, who stood hand in hand. 

 The longest length of real telegraph line through which I 

 have attempted to converse has been about 250 miles. 

 On this occasion no difficulty was experienced so long as 

 parallel lines were not in operation. Sunday was chosen 

 as the day on which it was probable other circuits would 

 be at rest. Conversation was carried on between myself, 

 in New York, and Mr. Thomas A. Watson, in Boston, 

 until the opening of bi;siness upon the other wires. When 

 this happened the vocal sounds were very much dimi- 

 nished, but still audible. It seemed, indeed, like talking 

 through a storm. Conversation, though possible, could 

 be carried on with difificulty, owing to the distracting 

 nature of the interposing currents. 



" I have had the opportunity of testing the telephone 

 upon the artificial cable owned by Sir William Thomson. 

 No difficulty was experienced in conversing through the 

 equivalent of 120 miles of submarine cable. Vocal 

 sounds were audible when the equivalent of the whole 

 Atlantic cable was interposed between the two telephones, 

 but the sounds were so faint that conversation could not 

 be carried on. Songs that were sung into one telephone 

 were readily recognised at the other end of the circuit, and 

 the articulation of pre-arranged sentences was readily 

 recognised. That the sounds were electrically produced 

 was evident from the fact that they ceased when the cir- 

 cuit was broken and when the coils of the telephone were 

 short circuited. No difference was observed between the 

 pitch of the note which was transmitted through the arti- 

 ficial cable and the same note when transmitted directly 

 through the air. The artificial cable experimented upon 

 had four times the resistance of the Atlantic cable, and 

 one-fourth its electrostatic capacity. I am informed by 

 my friend, Mr. Preece, that conversation has been success- 

 fully carried on through a submarine cable, sixty miles in 

 length, extending from Dartmouth to the Island of 

 Guernsey, by means of hand telephones." 



In a lecture on the 8th inst. at Glasgow, Prof. Bell, 

 referring to the use of the telephone in mines, pointed out 

 how the instrument might be of the greatest service in 

 determining whether the ventilation of a mine was perfect 

 or not ; for by listening to the telephone, if the mine was 

 in good order, a little sound could be heard every moment. 



AFRICAN EXPLORATION 



MR. STANLEY'S letter and the map in the Telegraph 

 of Monday enable us to realise somewhat more 

 fully the nature and extent of the discoveries made by the 



