88 LI. H. Bigelow—The Earth a Magnetic Shell. 
eaflected system exists around the magnetic poles, and an 
inflected system in the tropical belts. The problem before us 
is to obtain the value of the permeability or magnetic conduc- 
tivity of the earth, and the paths of the lines of force through 
the earth, that will conform to the observed external vectors. 
It will be remembered that this diagram represents the results 
of observations, without any admixture of theory or assump- 
tion of any kind. 
Fig. 3 
Vectors of the Polar Magnetic Field derived from Observation. 
p=2°0! H=0.00035. 
If a paramagnetic body or a diamagnetic body be plunged 
in a magnetic field of force, with the axis of magnetization, 
either permanent or induced, parallel to the direction of the 
field of force, then the following formule are applicable. 
