96 I’. H. Bigelow—The Earth a Magnetic Shell. 
fourth due to the change of the medium, as the immersion of 
the earth in the ether. The currents J, G, contain the con- 
duction, displacement and convection currents: 7, and g, are 
due to the motion of the impressed and intrinsic forces: E, H, 
the forces, D, B, the displacement and induction, p, o, the 
divergence, ¢, , the permittivity and inductivity. Some 
attempt has been made in this paper to give the value of yw for 
the earth. Several of the terms can be computed, since E. H. 
are approximately known for the electro-magnetic field, and the 
astronomical motions. We still need c. 
About the mode of magnetic radiation no serious hypothesis 
has been advanced, that is, how energy is propagated through 
the ether along these widespreading curved lines, whether by 
a rotary polarized wave or not. Yet the physical aspect of the 
case demonstrates that energy is continuously arriving at the 
earth from the sun. Now the question arises, is the term 
4ctVDG really wanting in nature, since this is the one corre- 
sponding to the electro-magnetic radiation VJB? Is it possible 
that this is the mode of propagation of the auroral energy, 
and if so what is the mechanical form ? 
We must distinguish between the mechanical pressure of 
radiant energy, and the amount of energy received at a sur- 
face per second. In the case of light, the pressure is due to 
the wave of H=0°02 C.G.8. E=6 x10, from which the maxi- 
mum translational force is 5 dynes per cu. cm. The action of - 
this field on the unit magnet pole is 0:00070 C.G.S. in the polar 
regions, and 0:00030 C.G.S. in the mid-latitude zone. The 
action on the same hemisphere from the polar magnetic field is 
000035 on the average, so that we have the same order of mag- 
nitude in both radiations to derive from the ether energy. The 
whole problem is obscure at present and can be developed 
properly only after the acquisition of further knowledge of the 
subject. If the portion of I due to radiation is 
. + eh oh 1 dW 
W=iUu GG. Ale U=gED=tcE* 
p =1U dit T=}ED=3,H’ 
where W=flux, U=density of radiant energy, p=pressure ; 
then p and W are related to temperature through the fourth 
power.’ Ue. | 
This to some extent outlines the path by which the external 
impressed energy is transformed into heat in the earth’s atmos- 
phere; and thence it passes into various meteorological circu- 
lations in the effort to restore equilibrium. Theoretical 
