TERRESTRIAL MAGNETO-ELECTRIC INDUCTION. 
169 
arranged thus : a sewing-needle had the head and point broken off, and was 
then magnetised ; being broken in half, the two magnets thus produced were 
stuck into a stem of dried grass, so as to be perpendicular to it, and about four 
inches asunder ; they were both in one plane, but their similar poles in con- 
trary directions. The grass was attached to a piece of unspun silk about six 
inches long, the latter to a stick passing through a cork in the mouth of a 
cylindrical jar ; and thus a compound arrangement was obtained, perfectly 
sheltered from the motion of the air, but little influenced by the magnetism of 
the earth, and yet highly sensible to magnetic and electric forces, when the 
latter were brought into the vicinity of the one or the other needle. 
164. Upon adjusting the needles to the plane of the magnetic meridian; 
arranging the ball on the outside of the glass jar to the west of the needles, 
and at such a height that its centre should correspond horizontally with the 
upper needle, whilst its axis was in the plane of the magnetic meridian, but 
perpendicular to the dip; and then rotating the ball, the magnet was imme- 
diately affected. Upon inverting the direction of rotation, the needle was 
again affected, but in the opposite direction. When the ball revolved from 
east over to west, the marked pole went eastward ; when the ball revolved in 
the opposite direction, the marked pole went westward or towards the ball. 
Upon placing the ball to the east of the needles, still the needle was deflected 
in the same way ; i. e. when the ball revolved from east over to west, the 
marked pole went eastward (or towards the ball) ; when the rotation was in 
the opposite direction, the marked pole went westward. 
165. By twisting the silk of the needles, the latter were brought into a 
position perpendicular to the plane of the magnetic meridian ; the ball was 
again revolved, with its axis parallel to the needle ; the needle was affected as 
before, and the deflection was such as to show that both here and in the 
former case the needle was influenced solely by currents of electricity existing 
in the brass globe. 
166. If the upper part of the revolving ball be considered as a wire moving 
from east to west, over the unmarked pole of the earth, the current of electri- 
city in it should be from north to south (99. 114. 150.) ; if the under part be 
considered as a similar wire, moving from west to east over the same pole, the 
electric current should be from south to north ; and the circulation of electri- 
MDCCCXXXII. 
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