506 MR. HARRIS ON THE POWER OF IRON TO CONTROUL THE MAGNET. 
such emanations cannot pass off in opposite directions at the same instant : 
now there is no sufficient reason why they should pass rather in one direction 
than another, and it therefore remains that an hypothesis which supposes them 
to pass in either, is quite unwarranted. The arrangement assumed by fine 
particles of iron, sifted on paper immediately over a magnet, arises out of the 
circumstance that the bar has generally a very sensible thickness; whilst the 
small particles of iron cannot operate beyond a certain distance a, b, c, 
and this equally applies to other cases in which the opposite sides of a magnet 
appear to attract at the same time. Moreover, the superficial boundaries of a 
magnet may be considered as so many distinct magnetic laminae of uncertain 
thickness, as is evident from the circumstance, that the magnetic centre and 
poles of one surface of a bar very frequently fall in a different way from those 
of another surface according to the trifling variations in the progress of mag- 
netizing ; and sometimes all the surfaces differ in this respect in the same bar, 
that is to say, the centre and poles do not correspond to the same relative 
points on any two sides. 
13. The wonderful phenomenon of magnetic attraction then is evidently 
the result of an impression first made on the magnet e, since with different 
masses of iron the attractive force at the same distance is unequal e : hence a 
magnet must be considered as a body in a peculiar state or condition, by which 
it may be caused to exhibit given powers or capabilities in consequence of 
external excitation. 
15. It is always difficult in inquiries of this nature to employ terms which 
shall seem altogether without objection. I trust therefore that those resorted 
to in the course of this paper, will be taken only in the arbitrary sense in 
which they have been used, and not as having any necessary connection with 
a particular set of opinions : thus the expressions neutralizing force, magnetic 
development, magnetic excitation, and so on, must be taken merely as arbi- 
trary terms, employed of necessity to facilitate the progress of inquiry, and to 
render its description as intelligible as possible, according to the general and 
unembarrassed acceptation of such terms. 
