l82 



NATURE 



\_yune 23, 1 88 1 



tertiary currents that superposed themselves upon the secondary. 

 In order to compare these spiral currents with those obtained 

 from a known helix, I found that takingacopper wire of similar 

 diameter (o"5 millim.), and winding it closely upon the steel 

 wire ten turns to each centimetre, having a total of 200 turns, 

 with an exterior diameter of I '5 millims., withdrawing the steel 

 wire, leaving this closely wound helix free, that it gave some 

 190°, instead of the 200 of the steel wire alone; thus the spiral 

 currents fully equalled a closely wound copper wire helix of 200 

 turns in a similar length. 



If it were possible to twist a magnetised wire several turns to 

 the right, and that its line of magnetism would coincide with 

 that of the twi^t, then on parsing a positive or negative current, 

 there would be an apparent augmented or diminished spirality of 

 the current, but both would have a right-handed twist. The 

 result would,beIidentical\vith the phenomenon described, although 

 the cause is different. 



The explanation of this phenomenon can be probably found in 

 the fact that the constant spirality now observed is that of the 

 electric current under which it was magnetism, for whilst magne- 

 tising it we had a powerful source of magnetism constantly 

 reacting upon the electric current, and the constant spirality now- 

 observed is the result or remains of a violent molecular reaction 

 at the instant of magnetisation, and the remaining evident path 

 or spiral is that of the electric current. On testing this wue as 

 to its longitudinal magnetic force, I found that it was less than 

 a wire simply magnetised in the usual way ; thus the effects are 

 internal, affecting the passage of the electric cun-ent, giving, 

 however, no external indications (except apparent weakness) of 

 the enormous disturbance which has taken place. 



3. RIolccular Sounds. — The passage of an intermittent current 

 through iron or other wire gives rise to .sounds of a very peculiar 

 and characteristic nature. Page in 1S37 first noticed these sounds 

 on the magnetisation of wires in a coil. De la Rive published a 

 chapter in his " Treatise on Electricity " (1S53) on this subject, 

 and he proved that not only were sounds produced by the 

 magnetisation of an iron wire in an inducing coil, but that sounds 

 were equally obtained by the passage direct of the current 

 through the wire. Gassiot, 1S44, and Du Moncel, 1878-S1, all 

 have maintained the molecular character of these sounds. Reis 

 made use of them in his, the first electric telephone invented, and 

 these soimds have been, since the apparition of Bell's telephone, 

 often brought forward as embodying a new form of telephone. 

 These sounds, however, for a feeble source of electricity, are far 

 too weak for any applied purposes, but they are most useful and 

 interesting where we wish to observe the molecular action which 

 takes place in a conducting wire. I have thus made use of these 

 sounds as an independent method of research. 



The apparatus was the same as in the last chapter, except no 

 telephone was used. The intermittent electric current was con- 

 nected by means of switch key, either 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. 



Iron of all metals that I have yet tried 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. 2S) is 

 best for loud sounds to be obtained by the direct passage of the 

 current, but large wires (i 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 longi- 

 tudinal 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 pireceding 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 

 S70 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 molec- 

 ular 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 longi- 

 tudinal 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 w ire 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 v\ ire is quite loose. A similar 

 but reverse action takes place as regards torsion ; for if the wire 

 is magnetised by the coil we obtain an almost complete zero of 

 sound by simply moving the torsion index 45° on either side, and 

 as this was the degree which gave silence in the previous experi- 

 ments for the same wire, it was no doubt due to the same 

 rotation of its polarised molecules. If we now pass a constant 

 current through the wire whilst the intermittent one is upon the 

 coil, we hear augmented sounds, not in pitch but loudness, and 

 if we give torsion of 45' to one side we have silence, or nearly 

 so, whilst the other side it gives increased tones which become 

 silence by reversing the battery. If whilst the wire by torsion 

 has been brought to zero, we decrease or increase the mechanical 

 longitudinal strain, then at once the polarised molecules are 

 rotated, giving loud sounds ; and we further remark that when 

 the wire is loosened, and we again tighten it, we gradually 

 approach a zero, and on increasing the strain the sounds return ; 

 thus we can rotate the molecules by a compound strain of torsion 

 and longitudinal strain. 



If we wish to notice the influence of a constant current passing 

 through the wire under the influence of the intermittent current 

 in the coil, we find that if the wire is free from torsion that on 

 passing the current the tones are diminished or increased according 

 to the direction of the current ; the tones then have an entirely 

 distinctive character, for whilst preserving the same musical pitch 

 as before, the tones are peculiar, metallic, and clear, similar to 

 when a glass is struck, whilst the tones due to longitudinal 

 magnetism are dull and wanting in metallic timbre. If we now 

 turn the index of torsion upon one side, we have a zero of sound 

 with or without the current ; but the opposite direction gives 

 increased tones whilst current is passing through the wire, but 

 zero when not. Here again a peculiarity of timbre can be 

 noticed, as although we have loud tones due only to the action 

 of the current through the wire, the timbre is no longer metallic, 

 but similar to that previously given out by the influence of the 

 coil ; evidently then the metallic ring could only be due to the 

 angular polarisation of the molecules, and when these were 

 rotated by torsion the tones were equally changed in its action 

 upon the wire. 



I have already shown that a permanent magnet brought near 

 the wire could rotate its polarisation, and it equally can produce 

 sound or silence in these molecular sounds (during that the wire 

 is at its zero of torsion, and a constant current sent through the 

 wire as in the last experiment). We find that either pole of the 

 natural magnet has equal effect in slightly diminishing the sound 

 by an equal but opposite rotation from the line of its maximum 

 effects ; but if the wire is brought nearly to zero by torsion, then 

 on approaching one pole of the natural magnet we produce a 

 complete silence, but the opposite pole at once rotates the mole- 

 cule to its maximum loudness, and on taking away the magnet 

 we have comparative silence as before. 



Heating the wire to nearly red heat by a spirit lamp increases 

 the tones of longitudinal magnetism induced by the coil some 

 25 per cent., but it has a much more marked increase on the 

 tones produced by the direct passage of the current where they 

 have more than 100 per cent, increase ; and if we pass the inter- 

 mittent current through the coil and constant through the wire, 

 we find no direct rotation of the molecules by heat, although 

 an apparent rotation takes place if we by the required torsion 

 first place the wire at its zero. Then on the application of heat 

 faint sounds are heard, which become again almost silent on 

 cooling; this is simply due to the diminution by heat of the 

 effect of the elastic torsion. 



Tempered steel gave exceedingly faint tones, requiring the use 

 of the microphone ; but on magnetising with a constant current, 



