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

THE GLACIAL PERIOD. ·31·
these two variations, the difference between the durations of summer
and winter would be the longest, when the eccentricity of the
earth is at its maximum and according as the winter and summer
occur at the points of perihelion or aphelion. It has been found
that this difference is equal to 33 days at the highest, and that at
the present day it is about 7½ days. Thus if the winter in the
northern hemisphere occurs when the earth is at P in its orbit
and the eccentricity is at its maximum, the winter will be shorter
by 33 days than the summer of the time. But this position will
be altered after 10,500 years when the winter, occurring at A,
will, in its turn, be longer than the corresponding summer by the
same length of time, viz., 33 days.
Now, since the earth describes equal areas in equal times in
its orbit, Herschel supposed that in spite of the difference between
the duration of summer and winter noticed above, the
whole earth received equal amount of heat while passing from one
equinox to another, the "inequality in the intensities of solar
radiation in the two intervals being precisely compensated by the
opposite inequality in the duration of the intervals themselves."
Accepting this statement Dr. Croll understated his case to a
certain extent. But Sir Robert Ball, formerly the Astronomer
Royal of Ireland, in his recent work On the Cause of an Ice Age
has demonstrated, by mathematical calculation, that the above
supposition is erroneous, and that the total amount of heat received
from the sun by each hemisphere in summer and winter varies as
the obliquity of the earth or the inclination of its axis to the
ecliptic, but is practically independent of the eccentricity of the
earth's orbit. Taking the total sun-heat received in a year by
each hemisphere to be 365 units, or on an average one
unit a day, and taking the obliquity to be 23° 27', Sir.
Robert Ball has calculated that each hemisphere would
receive 229 of these heat-units during summer and only 136