78 WRITINGS OF JOSEPH HENRY. [1832 



rod fifty two degrees, and from three fiftj'- nine degrees; but 

 ' when four helices were used, the deflection was only fifty five 

 degrees, and when to these were added the helix of smaller 

 wire around the armature, the deflection was no more than 

 thirty degrees. This result may perhaps have been some- 

 what affected by the want of proper insulation in the sev- 

 eral spires of the helices, it however establishes the fact that 

 an increase in the electric current is produced by using at 

 least two or three helices instead of one. The same princi- 

 ple was applied to another arrangement which seems to af- 

 ford the maximum of electric development from a given 

 magnetic power ; in place of the two pieces of iron and the 

 armature used in the last experiments, the poles of the mag- 

 net 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 surpris- 

 ing 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 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. 



In these experiments the connection of the battery with 

 the wires from the magnet was not formed by soldering, but 

 by two cups of mercury which permitted the galvanic ac- 

 tion on the magnet to be instantaneously suspended and the 

 polarity to be changed and rechanged without removing the 

 battery from the acid ; a succession of vivid sparks was ob- 

 tained by rapidly interrupting and forming the communi- 

 cation by means of one of these cups ; but the greatest effect 

 was produced when the magnetism was entirely destroyed 

 and instantaneously reproduced by a change of polarity. 



