184 MR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 
end of the copper cap. Upon rotating the magnet and its attached cylinder, 
abundance of electricity passed through the galvanometer, and in the same 
direction as if the cylinder had rotated only, the magnet being still. The 
results therefore were the same as those with the disc (218.). 
220. That the metal of the magnet itself might be substituted for the moving 
cylinder, disc, or wire, seemed an inevitable consequence, and yet one which 
would exhibit the effects of magneto-electric induction in a striking form. A 
cylinder magnet had therefore a little hole made in the centre of each end to 
receive a drop of mercury, and was then floated pole upwards in the same metal 
contained in a narrow jar. One wire from the galvanometer dipped into the 
mercury of the jar, and the other into the drop contained in the hole at the 
upper extremity of the axis. The magnet was then revolved by a piece of string 
passed round it, and the galvanometer-needle immediately indicated a power- 
ful current of electricity. On reversing the order of rotation, the electrical 
current was reversed. The direction of the electricity was the same as if the 
copper cylinder (219.) or a copper wire had revolved round the fixed magnet 
in the same direction as that which the magnet itself had followed. Thus a 
singular independence of the magnetism and the bar in which it resides is 
rendered evident. 
221. In the above experiment the mercury reached about half way up the 
magnet ; but when its quantity was increased until within one eighth of an 
inch of the top, or diminished until equally near the bottom, still the same 
effects and the same direction of electrical current was obtained. But in those 
extreme proportions the effects did not appear so strong as when the surface 
of the mercury was about the middle, or between that and an inch from each 
end. The magnet was eight inches and a half long, and three quarters of an 
inch in diameter. 
222. Upon inversion of the magnet, and causing rotation in the same 
direction, i. e. always screw or always unscrew, then a contrary current of 
electricity was produced. But when the motion of the magnet was continued 
in a direction constant in relation to its own axis , then electricity of the same 
kind was collected at both poles, and the opposite electricity at the equator, 
or in its neighbourhood, or in the parts corresponding to it. If the magnet be 
held parallel to the axis of the earth, with its unmarked pole directed to the 
