348 Mr. Christie on the magnetism of 
action not hitherto observed, they will not, I trust, be consi- 
dered unimportant. 
It has been stated that different effects will be produced on 
iron, as regards its polarity, when struck, twisted, filed, or 
scoured in different positions, with respect to the magnetic 
axis or line of the dip ; but I am not aware that it has ever been 
suspected that the simple rotation of iron, in different direc- 
tions, would have any effect on the manner in which the iron 
influenced a magnetic needle. This I have discovered to be 
the case ; and that the laws which govern this peculiar action 
on the needle are so general and uniform, that I have no doubt 
their causes are as steady in their operation, as those to which 
the more striking phaenomena of magnetism owe their origin. 
On observing these magnetical phaenomena arising purely from 
rotation, it appeared to me that they might possibly indicate 
the cause of the earth's magnetism ; and this was a further 
inducement to me thoroughly to investigate the circumstances 
connected with them. Before giving the particulars of these 
phaenomena, it is necessary that I should mention how I was 
first led to observe them. 
For some time previous I had been engaged in making 
several series of experiments, with a view to discover the 
precise manner in which unmagnetised iron acts upon a mag- 
netic needle. For this purpose I had made use of an iron 
ball 13 inches in diameter, and likewise of a shell i 8 inches 
in diameter, and observed their effects on the needle in vari- 
ous positions, as referred to certain planes passing through 
its centre. The shell and the needle were placed in the re- 
lative positions which I wished to give them, by determining 
a radius and an angle on an horizontal plane, and a vertical 
