Nebular Theory. — Mistoekles. 
365 
reach her orliit at perihelion, which shows that its rhstance 
from the Sun nuist have heen more than 70 milHon miles. 
It is, indeed, possihle. that its averajTc distance frf)m the 
Sun reached 100 million miles, and that it had its orbit out- 
side of the Earth ; but the most reasonable assumption is, that 
its average distance from the Sun was about 80 million miles, 
and that it, thus, reached several million miles outside of the 
Earth's orbit at apiielion. 
Now- since the Earth's nebula appeared inside of the 
Moon's aphelion-distance and outside of its average distance 
from the Sun, the Moon could not, for any length of time, 
escape crossing the orbit of the Earth to or from aphelion. 
The result would have been exactly the same, if its orbit had 
been just outside of the Earth's since this would have occas- 
ioned the Earth to have caught it at perihelion. 
In this manner, then, the M'oon w^as captured and became 
the satellite of the Earth, which the following illustration will 
serve to make clear. 
FtG. 1. 
The orbits of Venus, the Moon and the 
Earth, respectively, around the Sun. 
Fig. 2. 
The Moon captured by the Earth. 
We have spoken of the Moon as a planet when the Earth 
appeared as a nebula. It may be argued against this, that we 
lack proofs. If so, it is most fair to remark, that observations 
establish nothing more clearly than that the Moon is older 
than the Earth. Besides, it would not affect the result if eith- 
er the Earth or the Moon is the older, for even if the Earth 
had been a planet when the Moon assumed the shape of a 
