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The true key to the problem will be found, I believe, in a 
strict application of dynamical reasoning 1 to a vast dual system 
of matter and ether. It is confirmed by the double analogy of 
air and ocean currents on the surface of our globe. Radiant 
light and heat cannot be lost. If part travels out to other 
systems, the celestial exchanges cannot be all on one side. Our 
imports must surely balance, or nearly balance our exports. A 
small part only is arrested by the planets and satellites, and 
supplies their light and heat. A smaller portion may bo 
spent in repelling them from the sun, so as to counteract 
the effect of resistance, or in dilating nebulous matter in the 
equatorial zone of our system. But the main part, travelling 
out as ethereal motion, will transform itself at every step 
of the vast journey into ethereal condensation. There must 
plainly be an excess of motion in the parts of our system border- 
ing on the ecliptic and the sun's equatorial plane. There the 
ether will be thinned. As the heated water of the tropics 
flows north and south on the surface, and returns condensed 
and cooled in an undercurrent to the tropics again, so in this 
vaster and wider system. In the region of the outmost planets, 
and even beyond them, the ether must move in a steady, in- 
visible current to the polar regions of the great celestial sphere, 
which are not disturbed by the immense rotatory action ot the 
central mass. It will return to the sun, not as light and heat, 
but as ethereal compression, in the latent energy arising from 
an excess of density, and will then by the rotation be trans- 
formed into sensible light and heat once more. Such a circuit 
results demonstrably from the laws of physics, even so far as 
they are actually known. It answers to the double analogy in 
the currents of the air and the ocean. Instead of a waste-heap 
growing larger and larger, till all life, motion, and beauty are 
buried under the vast accumulation of a motion that will not 
move, and energy that lies idle and powerless, it reveals a grand 
scheme of circulation, akin to the systole and diastole ot the 
human heart. The sun might thus, without a miracle, dispense 
light and heat, undiminished, and perhaps even increased by 
further condensation, for millions of years or ages still to come. 
VI. Again, the doctrine that the earth consists of a thin 
crust, formed by cooling, on the surface of a sphere liquid 
with heat, was long accepted as an axiom of physics, and was 
current in all scientific manuals. A rude shock was first 
given to it by some papers of Mr. Hopkins, in which he 
showed that the phenomena of nutation required this solid 
crust to havo at least the thickness of many hundred miles. 
And now its reversal and rejection have become more complete. 
