214 



Prof. D. E. Hughes. 



[May 19, 



of electricity, an intermittent torsion nnder the influence of a con- 

 stant current of electricity or a constant magnetic field would pro- 

 duce similar currents. This was found to be the case, and as some 

 new phenomena presented themselves indicating clearly the molecular 

 nature of the actions, I will describe a few of them directly relating 

 to the subject of this paper. 



The apparatus used was similar to that described in my paper of 

 March 7th. An iron wire of 20 centims. was placed in the centre or 

 axis of a coil of silk-covered copper wire, the exterior diameter of the 

 coil being h\ centims., and that of the interior vacant circular space 

 centims. The iron wire is fastened to a support at one end, the other 

 passing through a guide, to keep it parallel to the axis but free, so that 

 any required torsion may be given to the wire by means of a connecting 

 arm or index. A sensitive telephone is in direct communication with 

 the coil, or a galvanometer may be used, as the currents obtained by a 

 f slow elastic torsion are slow and strong enough to be seen on a very 

 ordinary galvanometer. I prefer, however, the telephone, because it 

 has the inestimable advantage in these experiments of giving the exact 

 time of the commencement or end of an electric current. It has, 

 however, the disadvantage of not indicating the force or direction of 

 the current ; but by means of the sonometer the true value and direc- 

 tion of any current is at once given. Again, the telephone is useless 

 for currents -of slow intermittence ; but, by joining to it the microphonic 

 rheostat described in my paper of March 7th, a slowly intermittent or 

 permanent current is broken up into rapidly intermittent currents, and 

 then we are able to perceive feeble constant currents. For this reason a 

 microphonic rheostat is joined to the telephone and coil. The current 

 from a battery of two bichromate cells is sent constantly through the 

 wire if we wish to observe the influence of the torsion of the wire upon 

 the electric current, or a constant field of magnetic energy is given 

 to the wire by either a separate coil or a permanent magnet. The 

 currents obtained in the coil are induced from the change in the mole- 

 cular magnetism of the wire, but we may equally obtain these currents 

 in the wire itself without any coil by joining the telephone and 

 rheotome direct to the wire ; in the latter case, it is preferable to 

 join the wire to the primary of a small induction coil, and the tele- 

 phone and rheotome to the secondary, as then the rheotome does 

 not interrupt the constant electric current passing through the wire. 

 As the results are identical, I prefer to place the telephone on the coil 

 first named, as the tones are louder and entirely free from errors of 

 experimentation. 



If we place a copper wire in the axis of the coil we produce no 

 effect by torsion, either when under the influence of a constant mag- 

 netic field or a current passing through it, nor do we perceive any 

 effects if we place an iron wire (2 millims. in diameter), entirely free 



