वेदों की प्राचीनता एवं काल-निर्णय / ओरायन (लोकमान्य बाल गंगाधर तिलक - खगोलीय वैदिक शोध)

THE GLACIAL PERIOD. 27
is enormous; but in the present state of geological evidence it is
difficult to decide in favour of any one of these views. All that
we can safely say is that the duration of the Pleistocene period,
which included at least two Glacial and one Inter-Glacial epoch,
must have been very much longer than the period of time which
has elapsed since the commencement of the Post-Glacial period.
According to Sir Robert Ball the whole difficulty of finding
out the causes of the Glacial period vanishes when the solution of
the problem is sought for in astronomy rather than in geography.
Changes which seem to be so gigantic on the globe are, it is said,
but daily wrought by cosmical forces with which we are familiar
in astronomy, and one of the chief merits of Croll's theory is
supposed to consist in the fact that it satisfactorily accunts for a
succession of Glacial and Inter-Glacial epochs during the Pleisto-
cene period. Dr. Croll in his Climate and Time and Climate and
Cosmology has tried to explain and establish his theory by elaborate
calculations, showing that the changes in the values of the variable
elements in the motion of the earth round the sun can adequately
account for the climatic changes in the Pleistocene period. We
shall first briefly state Dr. Croll's theory, and then give the
opinions of experts as regards its probability.
Let PQ'AQ represent the orbit of the earth round the sun.
This orbit is an ellipse, and the sun, instead of being in the centre
C, is in one of the focii S or s. Let the sun be at S. Then the
distance of the sun from the earth when the latter is at P would
be the shortest, while, when the earth is at A it will be the longest.
These points P and A are respectively called perihelion and
aphelion. The seasons are caused, as stated above, by the axis of
the earth being inclined to the plane of its orbit. Thus when the
earth is at P and the axis turned away from the sun, it will produce