THE QUARTERLY 
HoOURNAL OF SCIENCE. 
JULY, 1875. 
EP eVARIATION INTHE; OBLIQUITY OF THE 
ECLIPTIC: 
By Colonel A. W. Drayson, R.A., F.R.A.S. 
PSHE problem of a variation, or possible variation, in the 
ah obliquity of the ecliptic, is one of the greatest interest 
and importance. As regards astronomy, it is a ques- 
tion which, although it may not materially affect observations 
made during short intervals, yet will produce most impor- 
tant changes after lengthened periods; and as regards our 
knowledge of astronomy, it is ten times as important to 
know whether the obliquity of the ecliptic can and has 
varied considerably, as it is to decide whether the sun 
is go or 95 million miles from the earth. When we 
examine this problem from a geological point of view, it is 
of even greater importance, for it would be the key to the 
solution of the climatic changes which are known to have 
existed on earth, and the records of which remain distinctly 
marked down to the present day. 
This problem is one which has not for some years attracted 
much attention, in spite of its paramount importance; the 
reasons for this neglect or indifference are probably the 
following: 
First, it has been generally supposed that the question of 
a variation in the obliquity was fairly and completely 
examined many years ago; that it was then proved as 
clearly as that the three angles of a plain triangle=180’, 
that the obliquity could vary only 1°21’; whatever, therefore, 
were the demands of geology for such an explanation as 
could be afforded by admitting a considerable variation in 
the obliquity, still it was supposed that the question had 
been long since disposed of, and nothing more remained to 
be done than to admit the impossibility of any variation 
greater than I’ ar’. 
The other reason why this problem has not been re-exam- 
ined appears to be that there is a belief that it is one which can 
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