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in a magnetized needle by an iron shell , &c. 
rioration (which we had no means of measuring) I have not 
attempted to give numerical results. 
After attentively considering Captain Wilson's experi- 
ments, and repeating some of them on my original apparatus 
at Woolwich, aided also by the explanation I had formed in 
my own mind as to the cause of these apparent anomalies, 
I was at length enabled to reduce the several results to a sort 
of general law, which may be thus enunciated. 
We may distinguish the following several cases of devia- 
tion and magnetic action between a magnetized needle and 
an iron ball or shell. 
1. The needle may be placed in any part of the magnetic 
meridian of such a ball ; in which case there is no deviation 
in the needle ; nor is there any secondary deviation by an 
unequal distribution of magnetism in its two branches. 
2. The needle may be placed any where in the magnetic 
equator of the ball. In this case, whichever end of the 
needle has its magnetism deteriorated, that end will approach 
the ball, and the same obtains generally while the poles of 
the needle are in opposite hemispheres of the ball. 
3. Generally, in other positions one branch of the needle 
will be nearer to the centre of the ball than the other; then, 
if the near end has its magnetism deteriorated, the needle 
will approach its natural meridian, but if the more distant 
end be deteriorated, the needle will be more deflected, or 
recede from the meridian. And this happens whether the 
near end lies between the ball and meridian, or the meridian 
between it and the ball. 
These however must be considered rather as general than 
as particular descriptions of the latter cases, because as the 
