OF FERRUGINOUS BODIES. 229 
50. The only hollow iron I then had at com- 
mand consisted of a few pieces of an old musket 
barrel, which had previously been cut for the 
purpose of forming a voltaic battery ; and subse- 
quently employed in the capacity of electro-mag- 
nets, in the series of inquiries then carrying on. 
51. One of the pieces, about a foot in length, 
was heated to as high a temperature as an ordi- 
nary house fire was capable of raising it to; at 
which temperature, when placed in the line of the 
dip, its magnetism entirely disappeared ; but re- 
turned as the temperature subsided, and eventu- 
ally displayed a higher degree of magnetic action 
on a compass-needle than it had shown previously 
to the heating process. 
52. With this fact, however, the inquiry rested 
for that time, the other proposed experiments 
being laid aside to give place to the electro-mag- 
netic inquiries then going on; and it was not till 
arranging the former section of this memoir, that 
my attention was again directed to the magnetism 
of ferruginous bodies at high temperatures. 
53. As my first repetition of Professor Barlow’s 
experimentshad been undertaken on a much smaller 
11 
