June 23, 1 881] 



NA TURE 



181 



galvanometer, we must time 'these movements with the oscilla- 

 tions of the needle ; but with the telephone it gives out con- 

 tinuous sounds for either movement, the interruptions bein;jonly 

 those caused by the rheotome. The direction of the current 

 has no influence on the result ; either positive to the free arm or 

 index or negative gives equal sounds, but at the moment of 

 reversal of the current a peculiar loud click is heard, due to the 

 rapid change or rotation of the polarisation of its molecules, and 

 this peculiarly loud momentary click is heard equally as well in 

 steel as in iron, proving that it i> equally polarised by the current, 

 but that its molecular rigidity prevents rotation by torsion. 



If a new soft iron wire of two millims. (giving no traces of a 

 cun-ent by torsion) has passed through it a momentary current of 

 electricity, and then the wire observed free from the current itself, 

 it will be found to be almost as strongly polarised as when the 

 current was constantly on, giving by torsion a constant of fifty 

 sonometric degrees. If, instead of passing a current through 

 this new wire, I magnetise it strongly by a permanent magnet or 

 coil, the longitudinal magnetism gives also 70° of current for the 

 first torsion, but weakens rapidly, so that in a few contrary 

 torsions only traces of a current remain, and we find also its 

 longitudinal magnetism almost entirely dissipated. Thus there 

 is this remarkable difference, and it is that whilst it is almost 

 impossible to free the wire from the influence produced by a 

 current, the longitudinal magnetism yields at once to a few 

 torsions. V/e may, however, transform the ring or transversal 

 magnetism into longitudinal magnetism by stron^jly magnetising 

 the wire after a current has passed through it ; this has had the 

 effect of rotating the whole of the molecules, and they are all 

 no%v symmetrical with longitudinal magnetism, then by a few 

 torsions the wire is almost as free as a new wire ; and I have 

 found this method nnre efficacious than heating the wire red hot, 

 or any other method yet tried. If I desire a constant cun-ent from 

 longitudinal magnetism, I place at one of the extremities of the 

 wire a large permanent magnet, whose sustaining power is five 

 kilometres, and this keeps the wire constantly charged, resem- 

 bling in some respects the effects of a constant current. The 

 m:ilecular magnetism or the current obtained by torsion is not so 

 powerful from this, my strongest magnet, as that produced by 

 the simple passage of a current, being only 50 sonometric 

 degrees in place of 70° for that due to the passage of a current. 

 The mere twisting of a longitudinal magnet, without regard to 

 the rotati m of its molecule having no effect, is proved by giving 

 torsion to a steel wire strongly magnetised, when only traces of 

 a current will be seen, perhaps one or two degrees, and a con- 

 stant source of magnetism or electricity then giving no measurable 

 effect. 



If we magnetise the wire whilst the cun-ent is passing, and keep 

 the wire constantly charged with both magnetism and electricity, 

 the currents are at once diminished from 70° to 30°. We have 

 hei'e two distinct magnetic polarisations at right angles to each 

 other, and no matter what pole of the magnet or of the current 

 the effect is greatly diminished ; the rotation of the two polar- 

 ities would now require a far greater arc than previously. The 

 importance of this experiment cannot as yet be appreciated 

 until we learn of the great molecular change which has really 

 occuned, and which we observe here by simply diminished 

 effects. 



If we heat the wire with a spirit flame, we find the sounds 

 increase rapidly from 70 to-90, being the maximum slightly below 

 red heat. I have already remarked in my previous paper this 

 increased molecular activity due to heat, and its effects will be 

 more clearly demonstrated when we deal with the sounds 

 produced by intermittent currents. 



2. Jiifluitice upon the Molsetilar Structure of an lion or Steel 

 11 ire by Electricity or Magnetism. — Being desirous to modify 

 the apparatus already described, so that it would only give in- 

 dications of a current if they were of a spiral nature, the wire 

 was kept rigidly at its zero of strain or torsion, and the coil was 

 made so that it could revolve on an axis perpendicular to the 

 wire ; by this means, if the wire was free from strain, the centre 

 or axis of the coil would coincide with that of the wire. Thus, 

 with a straight copper wire, we should have a complete zero, but 

 if this wire formed a right or left-handed helix, the coil would 

 require moving through a given degree (on an arbitrary scale) 

 corresponding to the diameter and closeness of the spirals in the 

 helix ; the degrees through which the coil moved were calibrated 

 in reference to known copper helices. 50" equalled a copper 

 wire I millim. diameter, formed into a helix of i centim. 

 diameter, whose spiral turns were separated I centim. apart. 



In order to obtain a perfect zen, and wide readings, with 

 small angular movement of the coil, it is necessary that the 

 return wire should be of copper, 2 millims. diame'er, offering 

 comparatively little resistance, and that it should be perfectly 

 parallel with the steel or iron wire. 



The rheotome is joined to a battery of two bichromate cells, 

 and by means of a reversing switch, an intermittent current of 

 either direction can be sent through the wire. The telephone is 

 joined direct and al me to the coil, thus no currents react upon 

 the coil when perpendicular to the iron, and its return wire if 

 not of a spiral nature. 



Placing an iron wire o'S diameter, and passing a current 

 through it, I found a change had taken place similar to those 

 indicated in my paper of March I7lh ; hut it was so difficult to 

 keep the wire free from magneti-m and slight molecular strains, 

 that I preferred and used only in the following experiments 

 teirpered steel wire (knitting-needles I found most useful). All 

 the effects are greatly augmented by the use of iron wire, but its 

 molecular elasticity is so great that we cannot preserve the same 

 zero of reading for a few seconds together, whilst with steel, 

 0"5 millim. diameter, the effects remained a constant until we 

 removed the cause. 



I have not as yet been able to obtain a steel wire entirely free 

 from magnetism, and as magnetism in steel has a remarkable 

 power over the direction of the spiral currents, I will first con- 

 sider those in which I found only traces. On passing the inter- 

 mittent current through these, the sounds were excessively feeble 

 for either polarity of current, but at each reversal a single loud 

 click could be heard, showing the instant reversal of the mole- 

 cular polarity. The d.greeof coil indicating the twist or spirality 

 of the current was 5° on each side of its true zero. Tine wire 

 was now carefully magnetised, giving 10° on each side for different 

 currents. The positive entering at north pole indicating 10° 

 right-handed spiral, negative entering the same pole, a left-h.inded 

 spiral, we here see in another form, a fact well known and de- 

 monstrated by De la Rive by a different method, that an electric 

 current travels in spirals around a longitudinal magnet, and that 

 the direction of this spiral is entirely due to which pole of an 

 electric current enters the north or south pole. I propose soon, 

 however, 'to show that under certain conditions these effects 

 are entirely reversed. 



If through this magnetised wire I pass a constant current of 

 two bichromate cells, and at the same time an intermittent one, 

 the spiral is increased to 15°, but the direction of the intermittent 

 current entirely depends on that of the constant current ; thus, 

 if the positive of the constant current enters the north pole, the 

 intermittent positive slightly increases the spiral to 17", and the 

 negative to 13°, both being right-handed ; the two zeros of the 

 constant battery are, however, as we might expect from the 

 preceding experiment, on equal opposite sides of the true zero ; 

 but if we magnetise the wire whilst a constant current is |iassing 

 through it, a very great molecular disturbance takes place ; loud 

 sounds are heard in the telephoie, and it requires for each cur- 

 rent a movement of the coil of 40°, or a total for the two currents 

 of 80°. Tliis, however, is not the only change that has taken 

 place, as we now find that both constant currents have a right- 

 handed spiral ; the positive, under which it was magnetised, a 

 right-handed spiral of 95° ; the negative, a right-handed spiral 

 of 15°, and the true central or zero point of the true currents 

 indicates a permanent spiral of 55°. 



This wire was magnetised in the usual way, by drawing the 

 north pole of my magnet from the centre to one extremity, the 

 south from the centre to the other, and this repeated until its 

 maximum effects were obtained ; in this state I found, sliding 

 the coil at different portions, that the spiral currents were equal, 

 and in the s.ame direction throughout. 



It now occurred to me to try the effect of using a single pole 

 of the magnet ; this was done whilst a constant current was 

 passing through the mre, commencing at the extremity, where 

 the positive joined, drawing the north pole through the length 

 of the wire, from positive towards the 'negative ; the effect 

 was most remarkable, as the steel wire now gave out as loud 

 tones as a piece of iron, and the degree on the coil showed 

 200°. The cinstant and intermittent currents now showed for 

 either polarity a remarkably strong right-handed twist ; the posi- 

 tive 200 right, and the negative 1 50 right-handed .spirals ; the 

 molecular strain on its wire from the reacHon of the electric 

 current upon the molecular magnetism was so great, that no 

 perfect zero would be obtained at any point, a fact already 

 observed when a wire was under an intense strain, producing 



