222 



Prof. D. E. Hughes. 



[May 19, 



except that no telephone was used. By means of a switch key the in- 

 termittent electric current was either connected with the coil inducing 

 longitudinal magnetism in the wire, or could be thrown instantly 

 through the wire itself, thus rapid observations could be made of any 

 difference of tone or force by these two methods ; a reversing key also 

 allowed, when desired, a constant current of either polarity to pass 

 through the wire under observation. 



Of all metals that I have yet tried, iron gave by far the loudest 

 tones, though by means of the microphone I have been able to hear 

 them in all metals ; but iron requires no microphone to make its sounds 

 audible, for I demonstrated at the reading of my paper, March 31st, 

 that these sounds with two bichromate cells were clearly audible at a 

 distance. A fine soft iron wire (No. 28) is best for loud sounds to be 

 obtained by the direct passage of the current, but large wires (1 millim.) 

 are required for equally loud tones from the inducing coil. By choosing 

 any suitable wire between these sizes we can obtain equal sounds from 

 the longitudinal magnetism or direct current. The wire requires to 

 be well annealed, in fact, as in all preceding experiments, the sounds 

 are fully doubled by heating the wire to nearly red heat. There are 

 many interesting questions that these molecular sounds can aid in 

 resolving, but as I wish to confine the experiments to the subject of 

 the two preceding chapters, I will relate only a few which I believe 

 bear on the subject. 



On sending an intermittent electric current through a fine soft iron 

 wire we hear a peculiar musical ring, the cadence of which is due to 

 that of the rheotome, but whose musical note or pitch is independent 

 both of the diameter of the wire and the note which would be given 

 by a mechanical vibration of the wire itself. I have not yet found 

 what relation the note bears to the diameter of the wire ; in fact, I 

 believe it has none, as the greatest variation in different sizes and 

 different conditions has never exceeded one octave, all these tones 

 being in our ordinary treble clef, or near 870 single vibrations per 

 second, whilst the mechanical vibrations due to its length, diameter, 

 and strain vary many octaves. 



I believe the pitch of the tone depends entirely upon molecular 

 strain, and I found a remarkable difference between the molecular 

 strain caused by longitudinal magnetism and the transversal or ring 

 magnetism produced by the passage of a current. For, if we pass the 

 current through the coil, inducing magnetism in the wire, and then 

 gradually increase the longitudinal mechanical strain by tightening 

 the wire, the pitch of the note is raised some three or four tones (the 

 note of the mechanical transversal vibrations being raised perhaps 

 several octaves) ; but if we tighten the wire during the passage of an 

 electric current through it, its pitch falls some two or three notes, and 

 its highest notes are those obtained when the wire is quite loose. A 



