121 
of hot iron between the white and blood-red heat. 
about 4 inches, by which means its upper extremity was the 
same height above the compass, and on repeating the expe- 
riment with the bar thus placed, we obtained an obvious devi- 
ation of the south end of the needle towards the iron of 4^ 
which remained fixed about two minutes. 
Having gained this by raising the bar 4 inches, we now 
raised it 6 inches, and on applying it in this place, we obtained 
a deviation of io-§-°, which remained fixed about the same 
time as before ; when the needle suddenly yielded to the 
natural magnetic power of the iron, and obtained almost in- 
stantaneously a deviation of 8i° the opposite way. 
It was thus rendered obvious, that the quantity of nega- 
tive attraction at the red heat, depended upon the height or 
depth of the centre of the bar from the compass ; and as the 
natural effect of the cold iron was changed by placing the 
compass below the centre of the bar, the question which 
naturally suggested itself was, will the negative attraction 
also change? To decide this point, we lowered our compass 
to within 6 inches of the bottom of the bar ; in w r hich position 
the cold iron necessarily attracted the south end of the needle, 
and produced a deviation of 21 0 . Upon heating the bar, we 
found, as usual, all its power upon the needle cease at the 
white heat; but as this subsided into the bright red, the ne- 
gative attraction began to manifest itself, and it soon amounted 
to io|°; the north end of the needle being attracted towards 
the iron. Here it remained stationary a short time, and then 
gradually returned, first due north, and ultimately to 70° go' 
on the opposite side. 
Having made these preliminary experiments, I was anxious 
to undertake a regular series, hoping by this means to be 
mdcccxxii. R 
