52: 



NATURE 



\_Marchi\, 1881 



possible. But by the aid of separate induction coils to convert 

 the f-ecoiidary into a tertiary, a perfect zero can be obtained if 

 the time of action and its force correspond to that which we 

 wish to measure. 



If I place a copper wire in the balance and turn the coils at an 

 angle of 45°, 1 obtain a current which can be perfectly balanced by 

 the jonouieter at 50°, proving, as already jaid, that it is secondary. 

 If I now replace ihe copper by an iron wire, the coil remaining 

 at 45°, 1 have again exactly the same value d r the iron as cop| er, 

 viz., 50°, and in both cases secondary. Now, it is evident that 

 in the case of the iron wire there was produced at each passage 

 of the current a strong electro-magnet, but this longitudinal 

 magnetism d d not either change the character of the current or 

 it^ value in force. 



A mcst beautiful demoUftration of the fact that longitudinal 

 magnetism produces no current, but that molecular magneii-^m 

 can act equally as well, no matter the direction of the longi- 

 tudinal magnetism, consists in forinii g an iron wire in a loop, 

 or taUinsi two parallel hut separate wires, joined electrically at 

 their fixed end-, the free ends being each connected with the 

 circuit, ;o that the current generated must pass up one wire and 

 down the adjacent one. On testing this loop, and if there are 

 no internal strains, complete jilence or ab.^-ence of current will 

 be found. Now, giving a slight torsicn to one of these wires in 

 a given direction, we find, say 50° positive ; twisting the parallel 

 wire in a similar direction produces a perfect zero, thus, the 

 current of the second must have balanced the positive of the 

 first. If, instead of twisting .t in similar directions, we twist it 

 in the contrary direction, the sounds are increased in value fr.im 

 50° positive to 100° positive, showing, in this latter case, not only 

 a twofold increase of force, but that the cun-ents in the iron 

 wires travelled up one wire and dow n the other, notwithstanding 

 that both were strongly magnetic by the influence cf the coil in 

 one direction, and this experiu ent also proves that its molar 

 magmetism had no efl"ect, as the currents are equally strong; in 

 both directions, and both w ires can double or efface the currents 

 produced in each. If instead of two wires we take four, we 

 can produce a zero, or a current of 200°, and with twenty wires 

 we have a force of looo°, or an electromotive force of two volts. 

 We have here a means of multiplying the effects by giving an 

 elastic torsion to each separate wire, and joining them electri- 

 cally in tension. If loops are formed of one iron and one 

 copper wire, we can oblain boih currents from the iron wire, 

 positive and negative, but none from the copper, its ivlc is 

 simply that of a conductor upon which torsion has no effect. 



I have already mentioned that internal strains will give cut 

 tertiary currents without any external elastic strain being put on. 

 In the case of iron wire these disappear by a few twists in both 

 directions, but in flat bars or forged iron they are more j:er- 

 manent ; evidently portions of these bars have an elastic strain, 

 whilst other portiims are free, for I find a difference at every 

 inch tested : the instrument however is so admirably sensitive 

 and able to point out not only the strain but its direction, that I 

 have no d.ubt its application to large forged pieces, such as 

 shafts or cannon, would bring out most interesting results, 

 besides its practical utility ; great care is therefore necessary in 

 these experiments that we have a wire free from internal strain--, 

 or that we know their value. 



Magnetising the iron wire by a large steel permanent magnet 

 has no effect whatever. A hard steel wire thus placed becomes 

 strongly magnetic, but no current is generated, nor has it any 

 influence upon the resuhs obtained from molecular movement, 

 as in elastic torsion. A flat wide iron or steel bar shows this 

 better than iron wire, as we can here produce transversal insiead 

 of longitudinal, but neither shows any trace of the currents \ ro- 

 duced by molecular magnetism. I have made many experi- 

 ments with wires and bars thus magnetised, but as the eflfect in 

 every case was negative when freed from experimental errors, I 

 will not mention them ; but there is one very interesting proof 

 which the instrument gives, that longitudinal magnetism fir.-,t 

 passes through its molecular condition before and during the 

 discharge or recomposition of its magnetism. For this purpose, 

 using no battery, I join the rheotome and telephone to the coil, 

 the w ire having no exterior circuit. If I strongly magnetise the 

 two ends of the wire, I find by rapidly moving the coll that 

 there is a Faradaic induction of 50° at both poles, but very little 

 or none at the centre of the wire ; now fixing the coil at the 

 central or neutral point of the wire and listening intently, no 

 sounds are heard, but the instant I give a slight elastic torsion 

 to the free pole, a rush of electric tertiary induction is heard, 



whose value is 40°. Again, testing this wire by moving the 

 coil, I find only a remaining magnetism of lo, and upon repeat- 

 ing the experiment of elastic torsion I find a tertiary of 5 ; thus 

 we can go on gi'adually di-charging the wire, but its discharge 

 will be found to be a recompo.-ition, and that it first passed 

 through the stage I have mentioned. 



Heat has a vei-y great effect upon molecular magnetic effects. 

 On iron it increases the current, but in steel the current is dimin- 

 ished. For experimenting on iron wire, w hich gave a tertiary cur- 

 rent of 50° positive (with a torsion of 20-j, upon the ap|;licalion of 

 (he flame of a spirit-lamp the force rapidly increases (cart being 

 taken net to approach red-heat) until the force is doubled, or 

 100 positive. The same effects were obtained in either direc- 

 tion, and wtre not due to a molar twist or thermo-current, as if 

 care had been taken to put on not more than 10° of tor>ion, the 

 wire came back to zero at once on removal of the torson. Hard 

 tempered steel, whose value was 10° whilst cold, with a torsion 

 of 45°, become cnly 1° when heated, but returned (if not too 

 n.uch heated) to S^ when cold. I very much doubted this ex- 

 periment at first, but on repeating the experiment with steel 

 several times I found that on heating it I had softened^ the ex- 

 treme hard (yellow) temper to that of the well-known blue 

 temper. Now at blue temper, hot, the value of steel was but V 

 to 2°, whilst soft iron of a similar size gave 50" of force cold, 

 and 100° at red heat. Now as I have already sh<iwn that the 

 effects I have described depend on molecular elasticity, it proves 

 at least, as far as iron and steel are concerned, that a compara- 

 tively perfect elas'ic body, such as tempered steel, has but slight 

 molfcular elasticity, and that heat reduces it, but that soft iron, 

 having but little molar elasticity, has a molecular elasticity of a 

 very high degree, which is increased by heat. 



The objects of the present paper being to bring the experi- 

 mental facts before the notice of the Royal Society, and not to 

 give a theoretical solution of the phenomena, I will simply add 

 that if we assume with Poisson that the paths of the molecules 

 of iron are circles, and that they become ellipses by compression 

 or strain, and also that ihey are capable of being polarised, it 

 would suflicitntly explain the new effects. 



Joule has show n that an iron bar is longer and narrower during 

 magnetisation than before, and in the case of the transverse 

 strain the exterirr portions of the wire are under a far greater 

 strain than those near the centre, and as the polarised ellipses are 

 at an angle with the molecules of the central portions of the 

 wire, its polarisation reacts upon them, producing the compara- 

 tively strong electric currents I have described. 



SCIENTIFIC SERIALS 



Transactions and Procadings of the Botanical Society of Edin- 

 burgh, vol. xiv., part I, 1881, contains — Address by the presi- 

 dent. Dr. T. A. G. Balfour (this address gave biief obituary 

 of J. M'Nab, Sir W. C. Trevelyan, Dr. M. Bain, Prof. Grise- 

 bach, A. Foibes, A. J. Adie, Dr. J. Cummins;, Karl Koch, Dr. 

 J. Murchison, Dr. D. Moore, P. S. Robertson, Wm. Mudd, 

 Dr. J. F. Th. Inniisch, S. Hay, Dr. M. A. E. Wilkinson, Rev. 

 W. B. Cunningham, E. V. Sandilands, and A. Graham). — Dr. 

 W. Traill, on the growth of Phormium tenax in the Orkney 

 Islands. — Wm. Gorrie, on the hardiness of New- Zealand plants 

 (1878-79). — Prof. G. Lawson, on British-American species of 

 Viola. — S. Grieve, flora of Colonsayand Uransay. — Jas. Blaikie, 

 botanical tour in Engadine. — Sir R. Christison, on the measure- 

 ment of trees. — Prot. J. H. jJalfour, on Rlieuni nobile. — P. M. 

 Thomson, the flow ering plants of New Zealand, and their rela- 

 tion to the insect fauna. — J. Sadler, on the flowering of Yucca 

 gloriosa. — Prof. Dickson, on the septa across the ducts in 

 Bougaiuvillca glabra, and Testudinaria elefhantipes . 



Proceedings of the Linnean Society of New South Wales, vol. 

 v., parts I and 2 (18S0). — F. M. Bailey, medicinal plants of 

 Queensland ; on Queensland ferns, with descriptions of two new 

 species; on a new species of Nepenthes.— M. A. Haswell, on 

 some Queensland Polyzoa, plates i to 3; on some new Amphi- 

 pods, plates 5 to 7. — Wm. Macleay, on a new species of 

 Galaxias, with remarks on the distribution of the species ; on a 

 new species of Otolith us and of Synaptura.— Rev. E. T. Woods 

 and F. M. Bailey, on the fungi of New South Wales and 

 Queensland.— Rev. E. T. Woods, on the littoral marine fauna 

 of North-East Australia ; on a fossiliferous bed at the mouth of 

 the Endeavour River; on the habits of some Australian Echini. 

 E. P. Ramsay, on a new species of Oligorus ; note on Galeo- 



