F. H, Bigelow—The Earth a Magnetic Shell. 95 
tions on Wildes’ Magnetarium were given, expressing a hope 
that the principles of a sphere rotating in external fields 
might be the ones to employ for this phenomenon. It would 
seem that this paper tends to confirm the suggestion in an 
important degree. 
From the analysis of the two external fields, it is seen that 
the shell of the earth in the mid-latitude zone (Europe) is 
traversed by two systems of lines of force, at right angles to 
each other: in the polar and tropical zones only in one direc- 
tion, that is along the meridians. It is quite clear from the 
observations on earth currents, that these are the prevailing 
directions, in the respective zones, their origin existing in the 
variable or spasmodic action of the solar field, disturbing the 
potential of the earth’s shell, the currents being the transfer- 
ence of energy in readjusting the equilibrium. The atmos- 
pheric electric potential has also been shown to be periodic 
with the external field, though the data are very meagre, and 
the dissipation of the magnetic radiations very probably has a 
term in static electricity. 
If the polar regions of the earth receive energy, in the form 
of magnetic radiation and this energy varies in intensity in 
short and long periods, then it is not far to seek in the sun as 
a variable star of very long period, in which the output goes 
through considerable changes from epoch to epoch, the cause 
of the glacial sheets that have alternately covered and retreated 
from the polar caps. As compared with the several astronom- 
ical theories of the cause of such great differences in heat, it 
seems more natural to extend our observed variations to cover 
the case of glacial periods. 
I have now stated my argument for believing in the exist- 
ence of the magnetic radiant energy from the sun, in addition 
to the electro-magnetic radiation, which has been so much 
studied during the past twenty years. The subject is new to 
science, because in general polar magnetic lines of force have 
not been regarded as radiant, only static. It is necessary to 
have a clear conception of the thing measured by the mag- 
netic instruments, namely the ponderomotive or mechanical 
force due to the stresses in the medium. Using Heaviside’s 
formula,* we have, 
Fe=EHp+[4z7VDG]+47VDg,—4E* Ac. 
Fm=[Ho|+VJB+Vj,B—$H’ A u. 
The first term is the static electrification and [magnetification 
= wanting]: the second is the pressure due to the wave propa- 
gation [magneto-electric = wanting] and the electro-magnetic: 
the third due to the motions of and through the medium: the 
* Hlectrical Papers, vol. ii, p. 562; Electro-magnetic Theory, vol. i, p. 107. 
