1832] WRITINGS OF JOSEPH HENRY. 77 



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

 method of producing electrical currents I have attempted * 

 to combine the effects of motion and induction; for this 

 purpose a rod of soft iron ten inches long and one inch and 

 a quarter in diameter, was attached to a common turning 

 lathe, and surrounded with four helices of copper wire in 

 such a manner that it could be suddenly and powerfully 

 magnetized, while in rapid motion, by transmitting gal- 

 vanic currents through three of the helices ; the fourth being 

 connected with the distant galvanometer was intended to 

 transmit the current of induced electricity; all the helices 

 were stationary while the iron rod revolved on its axis 

 within them. From a number of trials in succession, first 

 with the rod in one direction then in the opposite, and next 

 in a state of rest, it was concluded that no perceptible efifect 

 was produced on the intensity ol the magneto-electric current 

 by a rotary motion of the iron combined with its sudden 

 magnetization. 



The same apparatus however furnished the means of meas- 

 uring separately the relative power of motion and induction 

 in producing electrical currents. The iron rod was first 

 magnetized by currents through the helices attached to the 

 battery and while in this state one of its ends was quickly 

 introduced into the helix connected with the galvanometer; 

 the deflection of the needle in this case was seven degrees. 

 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 superiority 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 successful. 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 



