254 BULLETIN OF THE 



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 a horse-shoe 

 armature (admitting longer coils), Henry succeeded in obtaining 

 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 per- 

 fect 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 

 when 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 ex- 

 cited : in this case a small but vivid spark was seen to pass be- 

 tween 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 experiment of drawing sparks 

 from the magnet by Mr. James D. Forbes of Edinburgh who 

 obtained a spark on the 30th of March:* my experiments being 

 made during the last two weeks of June. A simple notification 

 of his result is given, without any account of the experiment, 

 which is reserved for a communication to the Royal Society of 

 Edinburgh. My result is therefore entirely independent of his, 

 and was undoubtedly obtained by a different process." 



Henry's gratification at the acquisition of the new insight into 

 natural law, quite absorbed all sentiment of personal pride in its 

 independent attainment; and his appreciation and congratula- 

 tion of Faraday as the first discoverer of magneto-electricit}', 

 were hearty and unreserved. He was also particular always to 

 assign to Faraday the first observation of the curious phenomena 

 of momentary galvanic induction; although himself an inde- 

 pendent discoverer of the fact. 



In the course of these experiments he made a very important 

 original observation on a peculiar case of self-induction, whereby 

 he was enabled to convert a galvanic current of "quantity" into 

 one of " intensity." This entirely new result seemed to contra- 

 dict all previous experience. He thus concludes his paper: "I 

 may however mention one fact which I have not seen noticed in 

 any work, and which appears to me to belong to the same class 

 of phenomena as those above described. It is this: — when a 

 small battery is moderately excited by diluted acid and its poles 



* Philosoph. Mag. and Annals, May, 1832, vol. xi. pp. 359, 360. 



28 



