202 CLASSICS OF MODERN SCIENCE 

 was entirely broken. The following extract from the register of the 

 experiments exhibits the relative deflections observed in one experi- 

 ment of this kind. 



At the instant of immersion of the battery, deflection 40° west. 



At the instant of emersion of the battery, deflection 18° east. 



Armature partially detached, deflection 7° east. 



Armature entirely detached, deflection 12° west. 



The effect was reversed in another experiment, in which the needle 

 was turned to the west in a series of deflections by dipping the battery 

 but a small distance into the acid at first and afterwards immersing it 

 by degrees. 



From the 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 induced 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 intensity of the iron. 



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

 of producing electrical currents I have attempted to combine the ef- 

 fects 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 mag- 

 netized, while in rapid motion, by transmitting galvanic currents 

 through three of the helices ; the fourth being connected with the dis- 

 tant 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 effect was produced on 

 the intensity of the magneto-electric current by a rotary motion of the 

 iron combined with its sudden magnetization. 



The same apparatus, however, furnished the means of measuring 

 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 de- 



