4 Prof. W. A. Norton on Terrestrial Magnetism. 
it is the main design of the present article to exhibit, and apply, 
although suggested by these views, is not necessarily dependent 
upon them. ‘The quantitative results arrived at, simply establish 
the existence of the forces supposed and of the relations conceiv- 
ed to subsist between them and the temperature of the earth. Dif- 
ferent views may be entertained of the physical origin of these 
forces; or, we may rest upon the forces themselves as so many 
primary properties of matter. 
The mechanical theory of the magnetism of the earth, of 
which I propose to give an exposition, is based upon the follow- 
ing fundamental principles. ‘These were obtained inferentially 
from the physical theory of terrestrial magnetism which has been 
briefly explained: but for our present purpose, they may be re- 
garded as mere assumptions, to be tested by the conclusions and 
results to which they lead. 
1. Every particle of matter at the earth’s surface, and to a cer- 
tain depth below the surface, is the centre of a magnetic force 
exerted tangentially to the circumference of every vertical circle 
that may be conceived to be tra- Fie. 1 
ced around it. Thus, if A, fig. 1, re 
be a particle of the earth’s mass 
at or near the surface, P a particle 
of a magnetic needle, and BPC 
ing also in oblique planes, I do not - 
here consider. If there are such forces it appears from the results 
of the investigation that they may be disregarded in the present 
inquiry. According to the views which have been offered of the 
probable physical nature of magnetism, the tangential forces here 
supposed are due to the transversal vibrations of the eth 
waves of magnetism propagated from the point A, and originat 
by certain vibratory movements of the particle at A. . 
2. The direction of this force will be different according @s It 
solicits the north or south end of the needle; and it is always 
such, that to the north of the acting particle the north end of t 
needle is urged downwards and the south end upwards, and 
and the south end in the direction Pm; and at P’ the north em 
will be solicited in the direction P/m’, and the south end in the 
