the Lines of Magnetic Force. 425 



steel, as very far beneath them ; next, perhaps, oxides of iron, 

 and so on by solutions of the magnetic metals to oxygen, water, 

 glass, bismuth and phosphorus, in the diamagnetic direction. 

 Taking the magnetic force of the earth as supplying the source of 

 power, and placing a globe of iron or nickel in the air, we see 

 by the pointing of a small magnetic needle (or in another case, 

 by the use of iron filings (3240.)), the deflected course of the 

 lines of force as they enter into and pass out of the sphere, con- 

 sequent upon the conducting power of the paramagnetic body. 

 These have been described in their forms in another place (3238.). 

 If we take a large bar-magnet, and place a piece of soft iron, 

 about half the width of the magnet, and three or four times as 

 long as it is wide, end on to, and about its own width from one 

 pole, and covering that with paper, then observe the forms of 

 the lines of force by iron-filings ; it will be seen how beautifully 

 those issuing from the magnet converge, by fine inflections, on 

 to the iron, entering by a comparatively small surface, and how 

 they pass out in far more diffuse streams by a much larger sur- 

 face at the further part of the bar, fig. 7. If we take several 

 pieces of iron, cubes for instance, then the lines of force, which 

 are altogether outside of them, may be seen undergoing success- 

 ive undulations in contrary directions, fig. 8. Yet in all these 

 cases of the globe, bar and cubes, I at least am satisfied that a 

 section across the same lines of force in any part of their course, 

 however or whichever way deflected, would yield the same amount 

 of effect (3109. 3218.) ; at the same time, this effect of deflec- 

 tion is not only consistent with, but absolutely suggests the idea 

 of a physical line of force. 



3293. Then the manner in which the power disappears in such 

 cases to an ordinary magnetic needle is perfectly consistent. A 

 little needle held by the side of the soft bar described above (3292.), 

 indicates much less magnetic power than if the iron were away. 

 If held in a hole made in the iron, it is almost indifferent to the 

 magnet ; yet what power remains shows that the lines through 

 the air in the hole are in the same general direction as those 

 through the neighbouring iron. These effects are perfectly well 

 known, no doubt ; and my object is only to show that they are 

 consistent with, and support the idea of external media having 

 magnetic conducting power. But these apparent destructions 

 of power, and even far more anomalous cases (2868. 3155.), 

 arc fully accounted for by the hypothesis ; and the force abso- 

 lutely unaffected in amount is found, experimentally, by the 

 moving wire. I have had occasion before to refer to the modi- 

 fication of the magnetic force (in relation to the magnetic needle), 

 where, its absolute quantity being the same, it passes across 

 better or worse conductors, and I have temporarily used the 



