122 Mr. Barlow on the anomalous magnetic action 
able to reduce this species of action to some fixed principle ; 
for it will have been observed, from what is stated above, 
that the negative attraction appeared to increase from each 
extremity of the bar towards its middle; whereas the posi- 
tive or natural action of the iron decreases in the like cases, 
and (passing through zero in the plane of no attraction) has 
its quality of attraction different when placed towards the 
upper or lower extremity of the bar. 
The negative attraction has also the same change of cha- 
racter in the upper and lower extremity of the bar; but as 
it increases towards the middle, it appeared to pass through 
a maximum to arrive at that change, which seemed wholly 
inexplicable; and I must acknowledge that, after all the 
experiments I have made, it still remains so. It is at all 
events certain, that the least change of position of the com- 
pass when near the centre of the bar, changes altogether the 
quantity and quality of this negative action. 
In the experiments detailed in the following table, I used 
four different bars, each 25 inches long, and 1^ inch square; 
two of them of cast iron, denoted in the first column by C. B, 
No. 1 ; C. B, No. 2 ; and two of malleable iron, denoted by 
M. B, No. 1, and M. B, No. 2. 
I had also two other bars, one of cast and one of malle- 
able iron, of the same dimensions, which were not heated, 
but kept as standards for determining the quantity of cold 
attraction, as this could not safely be done by the bars used 
in the experiments after being so repeatedly heated. 
The time employed in each experiment was about a quar- 
ter of an hour : the white heat commonly remained about 
3 minutes, when the negative attraction commenced ; this 
