Prof. D. Kirkwood on the Nebular Hypothesis. 169 
a condition of igneous fluidity. The moon may therefore be far- 
ther advanced in its physical history than the earth. On_ this 
subject Mr. Nasmyth, of Manchester, England, who has deyo- 
ted much time and attention to observations on the lunar surface, 
remarks as follows:—“ Having in my travels, seen the actual re- 
sults of volcanic action, extinct and active, 1 think I can com- 
prehend what I observe on the moon, and trace the analogy 
Im 
x 
ing phenomenon, having for its cause and source great cosmical 
mere chemical action ; 
and, in that view, I consider molten lava, and the heat of vol- 
active phenomenon will dwindle away, and finally cease to ex 
ist—the solid crust of the earth so increasing in thickness as to 
prevent the issue of any of the yet remaining molten matter 
om its interior, 
“The moon, from its small mass, and proportionally great sur- 
face, must kave cooled down much more rapidly than the earth; 
and all have been dead, tranquil and silent, for countless ages, 
ere we had passed over our rampant volcanic era, of which our 
he tremendous modern volcanoes are but mole-hills in com- 
ison, 
Jupiter and. Saturn.—What indications do the belts of Jupiter 
and Saturn afford in regard to the present physical condition of 
these planets? When our own planet was in a molten state, 
Where was the water which now constitutes our oceans ? It ed 
Necessarily have existed in the form of vapor, entirely surroun ‘| 
Ing the earth, and at a considerable distance fromit. Nor coul 
this water descend to, and remain perman ntly upon the surface, 
il Tong after the solidification of the crast by cooling. Dur- 
ig this “ pre-oceanic” period, our globe, 1b 18_! 
appeared 4 a diacat iasie tt much as Jupiter and Satur 
to 
d Saturn to cool down 
from their original molten and incandescent nese to such a 
1860. 
AM. JOUR. SCL-3ECOND SERIES, Vou. XXX, No. -SEPT., 
22 
