164 MR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 
that way being- the opposite to the course of the deflection taken in the former 
* 
general case. 
143. When the helix in any given position was inverted, the effect was as 
if a magnet with its marked pole downwards had been introduced from above 
into the inverted helix. Thus, if the end B were upwards, such a magnet in- 
troduced from above would make the marked end of the galvanometer needle 
pass west. Or the end A being upwards, and the soft iron in its place, inver- 
sion of the whole produced the same effect. 
144. When the soft iron bar was taken out of the helix and inverted in 
various directions within four feet of the galvanometer, not the slightest effect 
upon it was produced. 
145. These phenomena are the necessary consequence of the inductive mag- 
netic power of the earth, rendering the soft iron cylinder a magnet with its 
marked pole downwards. The experiment is analogous to that in which two 
bar magnets were used to magnetize the same cylinder in the same helix (36.), 
and the inversion of position in the present experiment is equivalent to a 
change of the poles in that arrangement. But the result is not less an instance 
of the evolution of electricity by means of the magnetism of the globe. 
146. The helix alone was then permanently held in the magnetic direction, 
and the soft iron cylinder afterwards introduced; the galvanometer needle 
was instantly deflected ; by withdrawing the bar as the needle returned, and 
continuing the two actions simultaneously, the vibrations soon extended through 
an arc of 180°. The effect was precisely the same as that of using a cylinder 
magnet with its marked pole downwards ; and the direction of motion, &c. was 
perfectly in accordance with those obtained in the former experiments with 
such a magnet (39.). A magnet in that position was then used, and gave the 
same deflections, but stronger. When the helix was put at right angles to the 
magnetic direction or dip, then the introduction or removal of the soft iron 
cylinder produced no effect at the needle. Any inclination to the dip gave 
results of the same kind as those already described, but increasing in strength 
as the helix approximated to the line of the dip. 
1 17- The cylinder magnet, although it has great power of affecting the 
galvanometer when moving into or out of the helix, has no power of con- 
tinuing the deflection (39.) ; and therefore, though left in, still the magnetic 
