382 Mr, Christie on the magnetism of 
the direction of rotation being given, we might point out 
immediately the direction in which the deviation would take 
place. 
On comparing together all the facts which I have detailed, 
I found that this might be effected in the following manner. 
I refer the deviations of the horizontal needle to the devia- 
tions of magnetic particles in the direction of the dip, or to 
those of a dipping needle passing through its centre ; so that, 
in whatever direction this imaginary dipping needle would 
deviate by the action of the iron, the horizontal needle would 
deviate in such a manner as to be in the same vertical plane 
with it : thus, when the north end of the horizontal needle 
deviates towards the west, and consequently the south end 
towards the east, I consider that it has obeyed the deviation 
of the axis of the imaginary dipping needle, whose northern 
extremity has deviated towards the west and its southern 
towards the east ; so that the western side of the equator of 
this dipping needle has deviated towards the south pole of 
the sphere, and its eastern side towards the north pole. It 
would follow from this, that if the north and south sides of 
the equator of the dipping needle (referring to these points 
in the horizon) deviated towards the poles, no corresponding 
deviation would be observed in the horizontal needle; the 
effect, in this case, taking place in the meridian, would only 
be observable in the angle which the dipping needle made 
with the horizon. As it is not my intention at present to 
advance any hypothesis on the subject, I wish this to be con- 
sidered only as a method of connecting all the phasnomena 
under one general view. Assuming it then for this purpose, 
it will be found that the deviations of the horizontal needle due 
