LINES OF MAGNETIC FORCE — OF ASSOCIATED MAGNETS. 
155 
circumstances there is, I think, no doubt that the external and internal forces of the 
same magnet have the same relation and are equivalent to each other, as was deter- 
mined in a former part of these Researches (3117.) ; and that therefore the equatorial 
section, which represents the sum of forces or lines of forces passing tlirough the 
magnet, remains also unchanged (3232.). 
3228. In this case the analogy with two or more voltaic batteries associated end to 
end in one circuit is perfect. Probably some effect, correspondent to intensity in the 
case of the batteries, will be found to exist amongst the magnets. 
3229. The increase of power upon a magnetic needle, or piece of soft iron placed 
between two opposite, favourable poles, is caused by concentration upon it of the lines 
which before were diffused, and not by the addition of the power represented by the 
lines of force of one pole to that of the lines of force of the other. There is no more 
power represented by all the lines of force than before ; and a line of force is not 
more powerful because it coalesces with a line of force of another magnet. In this 
respect the analogy with the voltaic pile is also perfect. 
3230. A line of magnetic force being considered as a closed circuit (3117-), passes 
in its course through both the magnets, which are for the time placed so as to act on 
each other favourably, i. e. whose lines coincide and coalesce. Coalescence is not 
the addition of one line of force to another in yoiver, but their union in one common 
circuit. 
3231. A line of force may pass through many magnets before its circuit is complete ; 
and these many magnets coincide as a case with that of a single magnet. If a thin 
bar-magnet 12 inches long be examined by filings (3235.), it will be found to present 
the well-known beautiful system of forces, perfectly simple in its arrangement. If it 
be broken in half, without being separated, and again examined, the manner in 
which, from the destruction of the continuity, the transmission of the force at 
the equator is interfered with, and many of the lines, which before were within 
are made to appear externally there, is at once evident, Plate IX. fig. 6. Of 
those lines, which thus become external, some return back to the pole which is 
nearest to the new place, at which the lines issue into the air, making their circuit 
through only one of the halves of the magnet ; whilst others proceed onward by 
paths more or less curved into the second half of the magnet, keeping generally the 
direction or polarity which they had whilst within the magnet, and complete their 
circuit through the two. Gradually separating the two halves, and continuing to 
examine the course of the lines of force, it is beautiful to observe how more and 
more of the lines which issue from the two new terminations, turn back to the 
original extremities of the bar, fig. 7? and how the portion which makes a common 
circuit through the two halves diminishes, until the halves are entirely removed from 
each other’s influence, and then become two separate and independent magnets. The 
same process may be repeated until there are many magnets in place of one. 
3232. All this time the amount of lines of force is the same if the fragments of the 
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