162 Prof. D. Kirkwood on the Nebular Hypothesis. 
view of the principal phenomena by which it is sustained; and 
thirdly, consider the most prominent of the objections which 
en urged against it. 
Asa group, our solar system is comparatively isolated in space; 
the distance of the nearest fixed star being at least seven thou- 
sand times that of Neptune, the most remote known planet. Be- 
sides the central or controlling orb, it contains, so far as known 
at present, sixty-seven primary planets, twenty-one satellites, 
three planetary rings, and nearly eight hundred comets. In ta- 
ing the most cursory view of this system of bodies, we cannot. 
fail to notice the following interesting facts in regard to the mo- ‘ 
tions of 1ts various members :— 
1. The sun rotates on his axis from west to east. 
2. The primary planets all move nearly in the plane of the 
sun’s equator. 
3. The orbital motions of all the planets, primary and second- os 
ary, except the satellites of Uranus and perhaps those of Nep- 
tune, are in the same direction with the sun’s rotation. : 
4, The direction of the rotary motions of all the planets, pri- 
mary and secondary, in so far as has been observed, is identical 
with that of their orbital revolutions; viz., from west to east. 
5. The rings of Saturn revolve about the planet in the same ; 
direction. 
6. ‘The planetary orbits are all nearly circular. 
7. The cometary, is distinguished from the planetary portion of 
the system by several striking characteristics : the orbits of com 
ets are very eccentric and inclined to each other, and to the 
ecliptic at all possible angles. The motions of a large proportion 
of comets are from east to west. The physical constitution of the 
latter class of bodies is also very different from that 
former; the matter of which comets are composed being so eX 
ceedingly attenuated, at least in many instances, that fixed stars 
have been distinctly visible through what appeared to be the 
densest portion of their substance. nt 
_ None of these facts are accounted for by the law of gravita- 
tion. The sun’s attraction can have no influence whatever in de- 
of 
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to east; in an orbit having any possible degree of inclination 1 
the pane of the sun’s equator, no less than in one coincident with 
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