492 THE GEOLOGIST. ■ 
Let B, E, and M be the sun, earth, and moon respectively ; and the last in con- 
junction with tiie first, as seen from the second. It will be sufficiently accurate for 
our present purpose to take the distance of the centres of the earth and moon 
as = 60 radii of the former body, the distance of the centres of the sun and moon 
as = 23,984 times the same unit, and the mass of the sun at 359,551 times that of 
the earth ; then, putting S and E to represent the attractions of the sun and earth 
on the moon, respectively, we have 
8 : E = 359551 x 60" : 1 x 23, 984* 
= 80899 : 35952 
=^9:4 nearly. 
So that the sun's claim to a visit from a * ' Lunar Sea" is greater than the earth's 
in the ratio of 9 to 4 ; and if the moon, according to the hypothesis, were formerly 
farther from the earth, she would be, by so much, nearer to the sun, when in con- 
junction ; and hence the attraction of the earth on the moon would be less, and 
that of the sun greater, at all earlier periods. 
Apologizing for the length of this letter, I am, yours, &c., 
Torquay^ Oct 12th, 1861. William Pengelli. 
To the Editor of the Geologist. 
SlR^ — Although the subject of the introductory paper of the October number 
of your justly popular journal more properly belongs to the science of Astronomy 
than Geology, yet, as some few of your many readers may be led from it to form 
unjust views of a by no means improbable reason which has been assigned for the 
absence of both air and water in appreciable quantities in that portion of the moon's 
surface which has ever been subjected to our observation, I think I may be excused 
for ofieriug a few remarks on this subject, more especially as they may suggest an 
answer to the query propounded, "Seeing there are waterless ocean (?) cavities on 
the moon, where have these waters gone to ?" 
It has long been a well- ascertained fact that the moon rotates on her axis, and 
performs her revolution round the eai'th in the same period of time ; it is also well 
known that if a stick loaded with a heavy weight at one end and a light one at the 
other be swung round by means of a string attached to the centre of this stick, that 
the heavy end will in the circulation assume a position further from the hand than 
the lio-ht one (see Hersch el's Outlines of A&tronomy, last edition, chap, vii.), hence 
it has been suggested by Professor Hansen, that the same cause which makes the 
heavier end of the stick describe the larger circle may in all probability be the 
reason why the moon always presents the same, or at least very nearly the same 
face to our eai-th, or, in other words, why the time of rotation on her axis and revo- 
lution round our earth coincide, namely, that in the moon, as in the stick, the centre 
of gravity does not coincide with the centre of symmetry. Let us now see what 
effect this would have on the distribution of water and air on the surface of a 
globe, as, although neither our moon nor the earth are truly circular, the difference 
of the effect produced in a globe of exactly the same figure as these bodies would be 
so small as in no way to affect the truth of our deductions or their applications ; 
then, first, let us take the case of a globe (fig. 1), in which the true centre, or centre 
of symmetry, and the centre of gravity coincide. In this case supposing the sur- 
