Mr. Barlow on the secondary deflections produced, &c. 277 
Helena, Bengal, and in China ; and he had the satisfaction 
of finding the sphere nearly inverted in his different expe- 
riments, the law in all cases strictly following those which 
had been predicted from my first series of results. 
The confirmation however of this fact is now of but se- 
condary interest, because it has been demonstrated, and 
admitted by all who have taken any part in the enquiry ; I 
shall therefore pass over these experiments, and mention 
only the curious observations alluded to in the title of this 
Paper. 
The apparatus which Captain Wilson employed was 
exactly similar to that which I made use of in Woolwich, viz. 
a large and strong round table with a hole in the centre, and 
a 13-inch mortar shell, with a contrivance for raising and 
lowering the latter through the centre hole. 
It appears that while in China, endeavouring to trace out 
the magnetic equator to the shell, which I have in my Essay 
called the circle of no attraction, or of no deviation, he found, 
that although in this circle no deviation was observed with 
the needle in its natural state, yet, if one end of the needle* 
(for example the south) was slightly touched with the south 
end of a magnet, a considerable deviation followed, and on 
repeating the experiments in different positions on the mag- 
netic sphere, different results were obtained ; the end of the 
needle, whose magnetism had been deteriorated, in some 
cases approaching, and in others receding from the centre of 
the ball. 
Captain Wilson having erected this apparatus at his house 
in town, I spent some time with him and Captain Beaufort, 
R. N. F. R. S. in examining and repeating these curious expe- 
