32 D. Trowbridge on the Nebular Hypothesis. 
when they were separated from the primitive solar spheroid. All | 
the satellites will be much smaller than the primaries; and, 
ing comparatively small bodies, they will cool down and be — 
? o 
given” a mathematical discussion of the retarding effect of 
the tides of the earth on its rotatory velocity. According to his 
circumference of the moon, or one period of rotation of the 
moon in a hundred years. Even if these numbers be wide of : 
the truth, the investigation shows us that, in general, the retard- ! 
ing effect of the attraction of the primaries on their secondaries, — 
whenin a fluid State, is sufficient, in the course of immense ages, 
to reduce the periods of revolution and rotation of the latter tog 
isochronism. We have, therefore, great reason to suppose that 
as a general rule the satellites turn on their axes but once during — 
@ revolution around their primaries. q 
47. If there exists a cosmical ether, as is at present pretty gen: 
erally admitted, in order that it may remain spread throughout — 
universal space, it is only necessary for it to possess an elasticity — 
tion of the ether around the sun would be in the general direc: 
tion of all the planets. It would also be regulated in its motion — 
ne id vil moon is on u m 
fourth | Se mnetet the earth—between 500 aed 600 miles for the Ketone wi 2 
eet of the earth upon the moon's equater, if it only partly fluid. If it be — 
wholly fluid, it would be somewhere ane 1000 miles per century. 
