115 



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 

 magnetic by contact with two bar magnets, or a common cylindrical 

 magnet of steel, similar results were still obtained. The arrange- 

 ment and the effects were simply these : several helices of copper 

 wire were formed, in the same direction, round a hollow cylinder of 

 pasteboard, metallic contact being prevented between the contiguous 

 coils : of these, either the alternate ends were united, to form owe long 

 helix, or all the corresponding ends to form a compound helix ; and 

 within the pasteboard cylinder, a cylinder of soft iron was intro- 

 duced: on the ends of this cylinder being brought into contact with 

 the poles of two bar magnets, united at the other ends so as to re- 

 semble a horse-shoe magnet, the needle of the galvanometer was 

 impelled in one direction, and on the contact being broken, in the 

 contrary. Similar effects were produced by simply introducing a 

 cylindrical steel magnet into the hollow cylinder over which the 

 copper wire was wound. The effects were strikingly increased, but 

 were still of precisely the same character, when Knight's large com- 

 pound magnet, belonging to the Royal Society, was substituted for 

 the bar magnets. Here, the mere approximation to the magnet, of 

 the compound helix, whether containing the cylinder of soft iron or 

 not, was sufficient to impel the needle in one direction, and its recess 

 from the magnet, to give a contrary impulse. But even here, the 

 effects were purely impulsive, the needle invariably returning to its 

 undisturbed direction, when the contact was continued. 



As in the voltaic arrangement, a small voltaic apparatus, sufficient 

 to deflect the needle of the galvanometer 30° or 40°, being intro- 

 duced between the galvanometer and the helix under induction, pro- 

 duced no effect on the impulses given to the needle, on making and 

 breaking contact of the iron cylinder with the magnet : nor did the 

 power of this arrangement appear to be affected after making the 

 contact or after breaking it. 



Although all attempts to obtain chemical effects or a spark in this 

 case failed, yet we agree with the author that these experiments 

 prove the production of electricity by ordinary magnetism, and think 

 the reasons which he adduces for its want of energy satisfactory*. 



* Since this report was written, a brilliant electric spark has been obtained 

 by Mr. Faraday and Mr. Christie with this magnet, by the very means which, 

 at this time, failed, in consequence of two contacts not taking place at the 

 same instant, on which circumstance the success of the experiment appears 

 entirely to depend. 



