OF FERRUGINOUS BODIES. 217 
played as those in the opposite direction ; and, 
what is very remarkable, though the causes of 
these apparently opposite movements of the poles 
are in operation during the whole period of the 
experiment, yet, at certain periods of the heating 
process, the force which urges the needle in one 
direction overcomes the force which urges it in 
the opposite one; and the needle, obeying the 
predominating force, moves accordingly. 
26. Having now given a general outline of the 
principal experimental inquiries that have been 
undertaken with a view of discovering the direct 
influence of caloric on the magnetism of ferrugi- 
nous bodies, I will proceed somewhat minutely to 
a detail of those which have, more recently, de- 
volved upon myself. 
