The sun. [volume] (New York [N.Y.]) 1833-1916, 1891-12-13
When Will America ana Europe Next
be Covered Over with Ice?

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When Will America ana Europe Next
be Covered Over with Ice?
The enunciation by sn RoBEnr BALL OF
the fact, which seems to have been frat
clearly brought to light by him. that OF the
total amount Of heat falling from tho sun
In q year. upon either the Northern or tho
Southern hemisphere. 0S per cent. Is re-
ceived in summer and 81 per cent. In winter.
has awakened renewed interest In the prob
lem Of tho glacial epochs. Dr.. BALLS tho
orem not only strengthens the astronomical
explanation Of the cause Of such epochs.
but nlso adds to its clearness. This expla-
nation may be summed up In few words.
It must BIO remarked. to begin with. that
tho summer and winter bore spoken Of d.
vide tho whole year between them. the eQui.
noctiA points marking the lines OF division.
spring and autumn being merged into tho
greater seasons. Everybody knows that
summer in the Northern hemisphere. count.
Ing summer as extending In the broader
sense Just mentioned from the vernal TO tho
autumnai equinox, is seven days longer
than winter. In the Southern hemisphere
just the opposite condition prevails. This
difference arises from the eccentricity Of
the earth's orbit. II tho orbit wero circle
instead Of an ellipso winter and summer
would b. Of equal length.
But tho elllpticai orbit Of the earth IL not
absolutely axed. either In form or In It's 20.
sition In space. Owing to tho varying at
fractions Of the other planets. and more par.
ticularly Of Venus and Jupiter. the earth's
orbit Is alternately rounded up almost into
circle. and then drawn out into more
ecccntrio ellipse. These changes require
vast intervals Of time. 80 that we must go
far back into the geological ages In order to
obtain evidence Of their effects upon the
earth. But it Is clear, theoretically. that
great seasonal vicissitudes must result from
such variations in the form Of the earth'B
orbit. When 1t approaches nearly to q cir
Gle. which is its condition now, the differ
ence in the length Of summer and winter is
small: when it IL In it's state Of greatest
eccentricity, the difference Is largo, amount
ing under the most favorable circumstances
to as much as thirty.three days, or some
authorities say even more. instead Of seven
days. it's present amount.
Now the theory In question asserts that
tho glacial epochs in the history OF the
when. the eccentricity Of the orbit being
large. the difference in the length of sum.
mer and winter was at or near Q maxi
mum. Under such circumstances one
hemisphere would have 100 days OF winter
and 166 days Of summer. while the other
hemisphere had l68 winter and 100 summer
days. But there would be no difference in
the distribution OF the heat coming from
the sun. Just 63 per cent. Of 1t would con-
tinue to DO received In summer and 81 per
cent. in winter in each hemisphere. The
hemisphere which had 1893 days Of winter.
would have to spread the 81 per cent. Of
heat belonging to that season over all those
1919 days. while tho O. per cent. of summer
heat would be concentrated upon the
shorter period OF lG6 days. Accordingly
there would be very long and cold winter.
followed by short and hot summer. The
heat of the latter would not suffice to melt
away the snow and ice accumulated during
the former. and this accumulation would
go on until whole continents were buried
under q blanket Of Ice thousands Of feet
thick. In the other hemisphere there would
be. on the contrary. a short. mild winter
and long summer. So glaclation In one
would be accompanied by genial
climatic conditions In the other.
Such is, in brief. the outline OF the as
Economical theory OF the cause Of glacial
epochs. We have purposely used the plural
in describing such epochs. although we
hoar only one Ice age spoken of.
because one OF the most interesting points
about this theory Ii that while accounting
for that age Of leo whose handiwork Is so
familiar to biologists In the Northern
it also demonstrates that there
must have boon many glacial epochs Of
varying intensity in the past. and that
there will be many mora In the future
This wonderful thing. the burying Of half
Of North America and the greater part Of
Europe under Ice. and the absolute destruc-
ton OF all their manifold forms Of life, can
then happen again, nay. must happen again.
Naturally. the question arises. when2 A
precise answer cannot DO given, owing to
the intricate nature OF the causes at work.
but 1t seems possible to give ON approx
mate answer. DR.. JAMES CHoLL. In his work
on Climate and Time" has computed the
periods OF greatest and least eccentricityof
the earths orbit for million years to
come, and for still greater period Of time
In the past. About $4,000 years ago the CO.
attained Its greatest possible
amount. From 100000 down to 5000 years
ago the orbit continued to be very eccen-
trio. and DR.. CRoLLs conclusion vas that
the latest Ice age In the Northern heml.
sphere ended with the close of tho period OF