Artic Home of the Aryans by Lokamanya Bal ... - Mandhata Global

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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 ease 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 during winter, whatever the eccentricity of the
earth may be. But though these figures are not affected by the
eccentricity of the orbit, yet we have seen that the duration of the
summer or winter does vary as the eccentricity.