236 MEMORIAL OF JOSEPH HENRY. 



opment of the magnetic action in one case and the sudden cessation 

 of it in the other. - - - From th'e foregoing facts it appears that 

 a current of electricity is produced for an instant in a helix of copper 

 wire surrounding a piece of soft iron whenever magnetism is in- 

 duced in the iron ; and a current in an opposite direction when the 

 magnetic action ceases ; also that an instantaneous current in one or 

 the other direction accompanies every change in the magnetic in- 

 tensity of the iron. 



" Since reading the account before given of Mr. Faraday's 

 method of producing electrical currents, I have attempted to com- 

 bine the effects of motion and induction." No increase of effect 

 was however observable. On comparing the two methods sepa- 

 rately it was found that while the sudden introduction of the end 

 of a magnetized bar within the helix connected with the galva- 

 nometer, deflected the needle seven degrees, the sudden magnetiza- 

 tion of the bar when within the helix deflected the needle thirty 

 degrees. A cylindrical iron bar was made to rotate rapidly on its 

 axis within a stationary helix, by means of a turning lathe, but no 

 result followed. 



In the following month (June) by employing an armature of 

 horse-shoe form (admitting longer coils), Henry succeeded in ob- 

 taining vivid sparks from the magnet. "The poles of the magnet 

 were connected by a single rod of iron bent into the form of a 

 horse-shoe, and its extremities filed perfectly flat so as to come in 

 perfect contact with the faces of the poles : around the middle of 

 the arch of this horse-shoe, two strands of copper wire were tightly 

 coiled one over the other. A current from one of these helices 

 deflected the needle one hundred degrees, and when both were used, 

 the needle was deflected with such force as to make a complete 

 circuit. But the most surprising effect was produced w T hen instead 

 of passing the current through the long wires to the galvanometer, 

 the opposite ends of the helices were held nearly in contact with 

 each other, and the magnet suddenly excited : in this case a small 

 but vivid spark was seen to pass between the ends of the wires, and 

 this effect was repeated as often as the state of intensity of the 

 magnet was changed. - - - It appears from the May number 

 of the ' Annals of Philosophy/ that I have been anticipated in this 



