INFLUENCE OF IRON IN THE MAGNETIC FIELD. 
9 
cause its approach to the iron. If the iron be applied in a similar manner at f, g, 
or h, it will have a like result in causing' motion of the bismuth ; and the parts 
marked h, c and d, will in turn approach it, seeming' to be attracted. If the soft 
iron do not touch the magnetic pole, but be held between it and the bismuth so as 
to represent generally the same positions, the same effects, but in a weaker degree, 
are produced. 
2488. Though these motions seem to indicate an effect of attraction, I do not 
believe them to be due to any such cause, but simply to the influence of the law of 
action (2479.) before expressed. The previously uniform condition of the magnetic 
field is destroyed by the presence of the iron ; lines of magnetic force, of greater in- 
tensity than the others, proceed from the angle a of the iron in the position repre 
sented, or from the corresponding angles in the other positions (the shape of the pole 
now approximating more or less to the conical or pointed form), and therefore the 
crystal of bismuth moves round on the axis of suspension, that it may place the line 
of magnecrystallic force parallel or as a tangent to the resultant of the magnetic 
forces which pass through its mass. 
2489. When in place of the group of crystals a crystalline plate of bismuth (2481.) 
is employed, the appearances produced under similar circumstances, are those of 
repulsion ; for if fig. 2 be allowed to represent this state of Fig. 2. 
things, the piece of iron applied at e causes the plate to 
recede from it at a, or if applied at f, g, or A, it causes re- 
cession of the bismuth from it at the points A, c, and d. 
Now though these effects look like repulsion, they are, as I 
conclude, nothing more than the consequences of the en- 
deavour which the bismuth makes, under the law before expressed (2479.), to place 
the magnecrystallic line of force parallel to, or as a tangent to the resultant of mag- 
netic force passing through the bismuth. 
2490. A piece of iron wire about inch long, and O'l or 0'2 of an inch thick, 
being held in the equatorial plane to the edge of the plate 
(fig. 3), did not alter its position; but if the end e were in- 
clined to either pole, the plate began to move, and moved 
most when the iron touched the pole as in the figure. 
When it approached or touched the N pole, the inclina- 
tion of the crystal plate of bismuth was as indicated by 
the dotted figure. When it touched the S, the inclina- 
tion was the contrary way. If the end e were kept in 
contact with the N pole, and the other end of the soft iron rod placed in the position 
m, the bismuth was not affected ; but if then this subsidiary pole were moved the 
one way or the other towards the edge of the plate, the latter turned as the pole 
moved, always tending to keep its face towards it, and evidently by the tendency of 
the magnecrystallic axis to place itself parallel to the resultant of magnetic force 
MDCCCXLTX. 
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