developement of magnetic al properties in steel and iron, &c. 219 
the metal, seems to overcome this resistance ; and, at the 
same time, disposes the iron for the retention of the mag- 
netism acquired. Now, on placing a wire or bar of soft 
steel upon this rod of iron, its magnetic virtue occasions 
some developement of the same power in the steel, which 
is increased by the tendency that percussion has to aid its 
developement in the steel, the same as it previously elicited 
in the iron. By continuing this treatment, the polarity of the 
steel is progressively augmented until it has acquired a max- 
imum, depending, not so much on its own capacity for mag- 
netism, as on the capability of the iron to develope it. But this 
condition, it has been shown, is only a maximum so long as 
the same iron bar or bars are used, and so long as their mag- 
netic energy obtains no augmentation ; for if by any means 
their polarity be increased, the attractive force of the steel 
wires will rise in proportion. From the whole phsenomena 
viewed in connection, it seems, that the simple general fact 
is this : — that percussion applied to magnetisable substances 
in contact with one another, disposes them to an equality of 
condition. 
If this view of the subject be correct, we have a satisfactory 
explanation of some of the phsenomena, which were other- 
wise obscure. We see why large bars, or wires of steel, 
(though they acquire a greater quantity of magnetic energy, 
as shown by their higher action on a compass needle, than 
small ones) do not attain any higher lifting powers than much 
smaller wires. (^Compare Experiments III. with VII., and 
XIV. with XVI. 3 And, above all, we have an explanation 
of the apparently contradictory propositions — that percus- 
sion diminishes, and has a tendency to destroy the energy of 
