504 
MR. HARRIS ON THE POWER OF MASSES OF IRON 
contact, or very nearly so, with the extremity of the magnet a (3). Let these 
small iron cylinders be now substituted in succession for the suspended iron b ; 
and being first nicely counterpoised, let the attractive forces be determined 
at a constant distance from the magnet A by means of the graduated scale s ; 
then these respective forces will be found to be very nearly in the same ratio 
as the previous powers of neutralization : in a great variety of cases they were 
found to be exactly in the same ratio. 
(/). Where the neutralizing power is equal, there the attractive force is also 
equal ; thus the neutralizing power, with a given magnet, not being greater in 
a cylindrical mass of iron of two inches in length than in one of an inch and 
half in length, no difference was subsequently found in the respective forces 
of attraction. 
10. The foregoing illustrations seem to throw some light on the manner in 
which magnetic action may be supposed to pervade bodies. 
(g). Having assigned any given distance, A b, Fig. 6, through which we know 
the influence of a magnet A can extend as estimated by some sensible measure b, 
then in interposing a third substance C in the space A b, the latter may receive 
a temporary magnetic state in two ways, either by the immediate action of the 
magnet A upon every particle of C, or otherwise by the propagation of mag- 
netism from particle to particle, or by both : now these operations seem to be 
in some inverse ratio of each other ; thus when the induced magnetic energy 
in C is considerable, the influence of the magnet A is more or less arrested by 
the laminae first acted on, which operate as screens on the succeeding ones ; 
so that the magnetic development after a certain distance proceeds entirely by 
propagation from one particle to another, until it is finally as it were expended ; 
and a body b which was before attracted at the distance A b will at the same 
distance now remain at rest c. Such is the case in interposing a screen of iron 
between a revolving magnet and a metallic disc ; but if the body C be low in 
the scale of magnetic energy, then the induced magnetic state is so weak that 
little or no screening influence is exerted between its particles, and the body 
b may be attracted as before : hence each particle of C will owe its magnetic 
development to the direct operation of the exciting magnet ; and it is only by 
the successive action of a great number of particles that we at length neutralize 
or cut off' the magnetic force by means of such a substance employed as a 
