This world
of ours, though usually steady enough in its movements, is at times
decidedly eccentric. Not that I mean to impute to our old and
exceedingly respectable planet any occasional aberrations of intellect,
or still less of morals (such as might be expected from Mars and Venus);
the word is here to be accepted strictly in its scientific or
Pickwickian sense as implying merely an irregularity of movement, a
slight wobbling out of the established path, a deviation from exact
circularity. Owing to a combination of astronomical revolutions, the
precession of the equinoxes and the motion of the aphelion (I am not
going to explain them here; the names alone will be quite sufficient for
most people; they will take the rest on trust)--owing to the
combination of these profoundly interesting causes, I say, there occur
certain periods in the world's life when for a very long time together
(10,500 years, to be quite precise) the northern hemisphere is warmer
than the southern, or _vice versa_. Now, Dr. Croll has calculated that
about 250,000 years ago this eccentricity of the earth's orbit was at
its highest, so that a cycle of recurring cold and warm epochs in either
hemisphere alternately then set in; and such cold spells it was that
produced the Great Ice Age in Northern Europe. They went on till about
80,000 years ago, when they stopped short for the present, leaving the
climate of Britain and the neighbouring continent with its existing
inconvenient Laodicean temperature.
Pages:
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143