( 306 ) (July, 
Ill.. THE PAST. HISTORY OF OUR ,MOOM 
By Ricuarp A. ProcrTor, B.A. (Camb.), 
Author’ of **The Sun,” “The. Moon,; sree 
\Jo HE appearance of two treatises upon the moon, both 
) of them considerable in dimensions, and within six 
months of each other, indicates the renewed interest 
which astronomers are taking in the study of the nearest of all 
the celestial bodies. It is noteworty, also, that in both these 
treatises,—in that by Nasmyth and Carpenter as well as in 
my own work,—the moon is regarded, not as a mere satellite 
of the earth, but asa planet, the least member of that family 
of five bodies circling within the asteroidal zone, to which 
astronomers have given the name of the terrestrial planets. 
There can be no question that this is the true position of 
the moon in the solar system. In fact, the fashion of re- 
garding her as a mere attendant of our earth may be looked 
upon as the last relic of the old astronomy in which our 
earth figured as the fixed centre of the universe, and the 
body for whose sake all the celestial orbs were fashioned. 
In this aspect, also, the moon is a far more interesting object 
of research than when viewed as belonging to another and 
an inferior order. We are able to recognise in her ap- 
pearances probably resulting from the relative smallness of 
her dimensions, and hence to derive probable information as 
to the condition of other orbs in the solar system which fall 
below the earth in point of size. Precisely as the study of 
the giant planets, Jupiter and Saturn, has led astronomers 
to infer that certain peculiarities must result from vastness 
of dimensions, so the study of the dwarf planets, Mars, our 
moon, and Mercury, may indicate the relations we are to 
associate with inferiority of size. 
This thought immediately introduces us to another con- 
ception which causes us to regard with even greater interest 
the evidence afforded by the moon’s present condition. It 
can scarcely be questioned that the size of any member of 
the solar system, or rather the quantity of matter in its 
orb, assigns, so to speak, the duration of that orb’s existence, 
or rather of the various stages of that existence. ‘The smaller 
body must cool more rapidly than the larger, and hence the 
various periods during which the former is fit for this or that 
purpose of planetary life (I speak with purposed vagueness 
here) are shorter than the corresponding periods in the 
life of the latter. ‘Thus the sun, viewed in this way, is 
