JOSEPH HENRY 203 



grees. The end of the rod was next introduced into the same helix 

 while in its natural state and then suddenly magnetized ; the deflection 

 in this instance amounted to thirty degrees, showing a great supe- 

 riority in the method of induction. 



The next attempt was to increase the magneto-electric effect while 

 the magnetic power remained the same, and in this I was more suc- 

 cessful. Two iron rods six inches long and one inch in diameter were 

 each surrounded by two helices and then placed perpendicularly on the 

 face of the armature, and between it and the poles of the magnet, so 

 that each rod formed, as it were, a prolongation of the poles, and to 

 these the armature adhered when the magnet was excited. With this 

 arrangement, a current from one helix produced a deflection of thirty- 

 seven degrees; from two helices both on the same rod, fifty-two de- 

 grees, and from three fifty-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 

 somewhat affected by the want of proper insulation in the several 

 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 principle was applied to another arrange- 

 ment which seems to afford 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 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 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 



