from a Natural Magnet. 199 



I have entirely employed ; and the subject of them has been a 

 very fine natural magnet, capable of supporting 170 Ib. presented 

 to the University by Dr HOPE. I willingly avail myself of this 

 opportunity to express my obligations to that gentleman for the 

 numerous and important facilities which have been afforded to 

 my researches, in his laboratory, where the magnet still is. 



My preliminary experiments demonstrated, by the action up- 

 on the multiplier and upon the frog, that a very powerful and 

 instantaneous current of electricity was conveyed through the 

 helix at the moment of making the contact of the connecting 

 iron with the magnet. My attention was then directed to such 

 an arrangement of apparatus as should by means of this current 

 produce a spark. Mr FARADAY had actually accomplished this 

 in the case of an electro-magnet, that is, by the conversion of a 

 soft iron bar into a magnet, by a galvanic current revolving round 

 it. He had, from another portion of the bar, been able to repro- 

 duce the electricity, and obtain a spark from it. 



In an early stage of my experiments I had, as far back as the 

 30th of March, obtained a spark from the magnet, which, how- 

 ever, being unable to repeat, from circumstances of which I af- 

 terwards became aware, I did not choose to publish at the time. 

 I accordingly proceeded closely to investigate the circumstances 

 : under which sparks were to be obtained from feeble galvanic 

 currents of low intensity. I used the common cylindrical elec- 

 tro-magnetic battery, in which, by varying the charge of acid, I 

 could obtain any required power. Thus I adjusted it till I ob- 

 tained from a momentary current nearly the same action on the 

 Multiplier as I had developed by the magnet. Removing it into 

 a dark place, I found that sparks were obtained at the instant of 

 making and breaking the circuit connecting the cups of the bat- 

 tery. Satisfied that I had a sufficient current of electricity, I pro- 

 ceeded to apply to the magnet the conditions which I had found 



c c 2 



