534 



Prof D. E. Hughes. 



[Mar. 17, 



of current will be found. Now, giving a slight torsion 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 it in similar directions, we twist it in the con- 

 trary direction, the sounds are increased in value from 50° positive to 

 100° positive, showing, in this latter case, not only a twofold increase 

 of force, but that the currents in the iron wires travelled up one wire 

 and down the other, notwithstanding that both were strongly 

 magnetic by the influence of the coil in one direction, and this 

 experiment also proves that its molar magnetism had no effect, as the 

 currents are equally strong in both directions, and both wires 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 1,000°, 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 

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

 copper wire, we can obtain both currents from the iron wire, positive 

 and negative, but none from the copper, its role is simply that of a 

 conductor upon which torsion has no effect. 



I have already mentioned that internal strains will give out 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 permanent ; evidently, 

 portions of these bars have an elastic strain, whilst other portions are 

 free, for I find a difference at every inch tested : the instrument, how- 

 ever, is so admirably sensitive, and able to point out not only the 

 strain, but its direction, that I have no doubt its application to large 

 forged pieces, such as shafts or cannon, would bring out most interest- 

 ing results, besides its practical utility ; great care is therefore neces- 

 sary in these experiments that we have a wire free from internal 

 strains, 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 results 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, instead of longitudinal, but neither shows 

 any trace of the currents produced by molecular magnetism. I have 

 made many experiments with wires and bars thus magnetised, but as 

 the effect 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 first 

 passes through its molecular condition before and during the discharge, 



