ON THE LINES OF MAGNETIC FORCE. 
:i7 
Other times it was 6 or 8 feet long and extended to a great distance. The deflection 
due to ten revolutions of the magnet was observed, and the average of several 
observations, for each position of the wire, taken : these were very close (with the 
precautions before described) for the same position; and the averages for different 
positions agreed perfectly together, being 9°‘5. I endeavoured to repeat these expe- 
riments on distance by moving the wire and preserving the magnet stationary in 
the manner before described (3091.) ; they were not so striking because time would 
only allow of smaller deflections being obtained (3104.), but the same numljer of 
journeys through an arc of 180° gave the same deflection at the galvanometer, 
whether the course of the wire was close to the magnet or far off; and the deflec- 
tion agreed with those obtained when the magnet was rotating and the wire at rest. 
3108. As to velocity of motion ; when the magnet was rotating and the wire placed 
at different distances, then ten revolutions of the magnet produced the same deflec- 
tion of the needle, whether the motion was quicker or slower, and whatever the 
distance of the wire, provided the precautions before described were attended to 
(3104.). That the same would be true if the wire were moving and the magnet still, 
is shown by this ; that whatever the velocity with which the wire and magnet revolve 
together, and whatever their distance apart, they exactly neutralize and equal each 
other (3096.). 
3109. From these results the following conclusions may be drawn. The amount 
of magnetic force, as shown by its effect in evolving electric currents, is determinate 
for the same lines of force, whatever the distance of the point or plane, at which their 
power is exerted, is from the magnet. Or it is the same in any two, or more, sections 
of the same lines of force, whatever their form or their distance from the seat of the 
power may be. This is shown by the results with the magnet and the wire, when 
both are in the circuit (3108.) ; and also by the wire loop revolving with the magnet 
(3092.) ; where the tendencies of currents to form in the two parts oppose and exactly 
neutralize or compensate each other. 
3110. In the latter case very varying sections outside of the magnet may be com- 
pared to each other ; thus, the wire may be conceived of as passing (or be actually 
formed so as to intersect) lines of force near the pole, and then, being continued along 
a line of force until over the equator, may be directed so as to intersect the same 
lines of force in the contrary direction, and then return along a line of force to its 
commencement; and so two surface sections may be compared. It is manifest that 
every loop forming a complete circuit, which is in a great plane passing through tlie 
axis of the magnet, must have precisely the same lines of force passing into and passing 
out of it, though they may, so to say, be expanded in one part and compressed in 
another ; or (speaking in the language of radiation) be more intense in one part and 
less intense in the other. It is also as manifest, that, if the loop be not in one plane, 
still, on making one complete revolution, either with or without the magnet, it will 
have intersected in its two opposite parts an exactly equal amount of lines of force. 
