62 Royal Society. 



one being interposed between those of the other, and metallic con- 

 tact everywhere prevented. The ends of one wire were connected 

 with a galvanometei-, and with the ends of tlie other, contact could 

 be made or broken with a battery of one liundred and twenty pairs 

 of plates. On the contact with the battery being made, the needle 

 of the galvanometer was invariably impelled in one direction, and on 

 the interruption of the contact, it was always impelled in the con- 

 trary. After the first impulse on the completion of the voltaic 

 circuit, the needle resumed its natural position, no permanent deflec- 

 tion whatever occurring during the time that this circuit remained 

 complete. 



On substituting a helix of copper wire formed round a glass tube 

 for the galvanometer ; introducing a steel needle; making contact, 

 as before, between the battery and the inducing wire ; and then 

 withdrawing the needle, previously to breaking the battery contact, 

 it was found to be magnetised. If the contact was first made ; a 

 needle introduced in the tube ; the contact broken ; the needle on 

 being withdrawn was found to be magnetised to the same degree 

 nearly as the first, but the poles at the corresponding ends were of 

 the contrary kind. 



If the circuit between the wii-e under induction and the galvano- 

 meter was not complete when the contact with the battery was made, 

 then no effect on the needle was observable either on completing or 

 again breaking the first circuit. But the battery communication 

 being_^r4< made, and then the wire under induction connected with 

 the helix containing the needle, on interrupting the battery circuit, 

 the needle was magnetised. These last facts, in a theoretical point 

 of view, are most important : they prove that on completion of the 

 voltaic circuit, the state of the wire under induction undergoes a 

 double change, the one momentary, the other permanent so long as 

 the voltaic circuit remains complete, and only exhibiting a momen- 

 tary action on the interruption of that circuit. 



From the experiments detailed in this section, the author con- 

 cludes, that currents of voltaic electricity produce, by induction, 

 currents (but which are only momentary) parallel to or tending to 

 parallelism with the inducing currents ; that the induced current, by 

 the first action of the inducing current, is in the contrary direction 

 to, and by its cessation in the same direction as, that of the inducing 

 current. 



The author next introduced iron into his arrangement, by which 

 means a double induction took place, the iron itself becoming mag- 

 netic by induction, in the first instance, and electricity being induced 

 in the copper wire from the magnetised iron, in the second. The 

 effects were here of precisely the same character as before, but 

 greatly increased. By this arrangement unequivocal evidence of 

 electricity in the wire under induction was obtained ; for not only 

 •was the needle in the galvanometer violently affected, but a minute 

 spark could be perceived on using charcoal at the ends of that wire. 



On dispensing altogether with the voltaic arrangement, and sub- 

 stituting for the electro-magnet a cylinder of soft iron, rendered 



