294 Variation in the Obliquity of the Ecliptic. [July, 
The calculations made of the effet produced by the moon 
and sun on the rotating earth, when the centre of gravity 
was in one position, could not hold good,—nor would the 
effects be the same when the centre of gravity was situated 
in another position. It may appear that the effects resulting 
from such a cause would be slight, but it must be remem- 
bered that whatever effect is produced during one rotation 
of the earth would have to be multiplied by upwards of 
9,000,000 to obtain the effect during one revolution only of 
the equinoxes ; and as 25,000 years is but a small portion of 
time when compared to the long epochs required by Geology 
for different periods, it will be seen that this is by no means 
a fact to be neglected or ignored. 
We know, from the researches of geologists, that there 
was in former times a vastly different distribution of land 
and sea to that which now prevails. We know that this 
cause would have produced, by the transfer of the water of 
the ocean, a change in the position of the centre of gravity 
of the earth ; and, as mechanicians, we know that it is im- 
possible to alter the position of the centre of gravity of a 
rotating body without altering the movement which the axis 
of this rotating body may at the time be making. Conse- 
quently it follows—if the statement made by geologists be 
true—that, in former times, continents now above the sea 
were formerly below that level, and that the change in 
direction which the earth’s axis now exhibits is not that 
which it formerly pursued ; and as the value in the obliquity 
of the ecliptic is dependent on the course pursued by the 
earth’s axis, it may be affirmed that the variation in the 
obliquity to a considerable amount is not only possible, but 
is most probable. 
The question of this great change in the obliquity is, we 
claim, one which cannot be definitely and arbitrarily settled 
by making certain calculations relative to the attraction of 
the sun and moon on the protuberant mass at the equatorial 
regions of the earth, and ignoring all other facts. It is one 
which no mathematician can deal with correctly, whilst he 
ignores or overlooks the fact of the present probable position 
of the earth’s centre of gravity, and of the certainty of this 
centre having formerly been located elsewhere, and also of 
there having been many changes in its position due to the 
transferral of the waters of the ocean, in consequence of the 
many elevations of land in various parts of the earth in 
former times. 
As a summary of this problem we may give the fol- 
lowing :— 
