i 
induced in iron bodies by rotation, 319 
I afterwards found, that the needle being placed in diffe- 
rent situations, its motion was reversed, although the direc- 
tion of motion in the shell was the same ; the amount of the 
whole deflection also differed very considerably according 
to the situation of the compass, its direction in some cases 
having been wholly reversed, while in others no perceptible 
motion was produced, although the rotation of the shell 
remained the same both in direction and in speed. 
I was therefore desirous of undertaking a regular set of 
experiments, in order to reduce the several apparently ano- 
malous results to some certain law of action ; and as the 
shell in question was rather too heavy for us to feel a perfect 
security, as to personal safety, when it was in rapid rotation, 
and moreover, as its effects were larger than seemed neces- 
sary for the purpose, I now selected a Shrapnel shell of 
8 inches in diameter, which weighed only 30 lbs. and chose 
another lathe, whose axis was nearly north and south, that 
in the former instance having been east and west. I had 
also a table made with a circular hole in it, which I could 
place at any height above, below, or about the centre of the 
ball : I could also set my compass on any azimuth on the 
same, and observe the effects of the direct and reversed mo- 
tion ; but after several days observations, I found the results 
so complicated, and the needle so much influenced by the 
iron work of the lathe and other machinery, that it would be 
useless to proceed, unless I could contrive to produce the 
rotation out of the way of any disturbing cause of the kind 
above mentioned. 
This also, through the kindness of Colonel Sir Alexander 
Dickson, and the officers above named, I was enabled to 
