The daily dispatch. [volume] (Richmond [Va.]) 1850-1884, 1866-08-29
Y....-...,n. 10 scientific Men.

At the recent Scientific Convention held
IN one of the northern States Professor
Uilgard said he proposed to say few
words on the probable causes of the
changes Of climate which produced the
glacial period. If we could assign any
cause adequate to producing On excess OF
winter precipitation over winter cvapora-
ton, however small at first, and continued
over great number of years, we should
have no difficulty in accounting for an &C
cumulation Of snow sufficient to account
for all the glacial phenomena. Such q
cause is to be found in change OF the
cccentricity of the earth's orbit around the
sun, which has lately been shown by lie
Verrier to have at various times been far
greater than at present. Suppose the &C.
centricity to have been such that the ell
feet of differences Of distance from the
sun at opposite points of the orbit be
nearly canal to the effect of the incllna-
ton of the axis, which is what produces
orr present differences of climate. Let the
southern hemisphere be that which has It's
summer in perihclion and its winter III
anhclion, as at present. Its SUMMERTIME
neriod from the vernal to the autumnal
misunderstanding with its greatest
distance from the sun, would De
cooled, while its winter would DC
warmed by its greater proximity to the
sun, so as to produce a nearly equable,
moderate climate throughout the year.
The other hemisphere, on the contrary,
would have its seasons greatly eXagge-
rated having a short, hot summer in per-
helion, and a long, cold winter in aphelon.
1t is true, the total amount of heat re.
ceiyed from the sun between the vernal
and autumnal equinoxes would be pre-
cisely equal to that received during the
complement of the year, brit the amount
radiated into space would he prOportioned
to the time. The average temperature OF
the globe always remains the same, but its
distribution becomes very different from
what it is now. The heat of the short
summer is insufficient to melt all the
SHOWS of the long winter; from year to
year q greater accumulation of snow takes
place. The effect is, the air is charged
with vapor during the summer; the sky
covered with n dense cloud, prevents the
penetration of the suns rays, as we see it
on days when thaw sets in after fall OF
snow.
The period during which by the revolu-
ton of the axis Of the earth's orbit each
hemisphere passes from the stage from
perpetual spring through every interme-
diate climate to that Of glacial condi-
ton, and back again to the former state,
is about twenty-five thousand years. The
ranges in the ecccntricity of the earth's
orbit are of much longer period and very
complicated, with irregular recurrence
About one hundred and forty thousand
years ago the value of the eccentricity
was such as to produce the condition de-
scribed. At several distant periods SINH
lar conditions have obtained, especially
about eight hundred thousand years ago
when perhaps glacial period previous to
the carboniierous may have taken place
For fifty thousand years past it has been
and for one hundred thousand years to
come it will remain, very small, as it is
: now. Both hemisphercs would be alter.
nately subjected to these changes. We
have here an explanation based on known
principles, and atiording ample time fol
the effects to be produced without invo
king violent commissions or cataclysms o
nature. At no time arere the changes inpro
gress more rapid than they are nou.
Professor Hall said that much credit wa
! due to Professor Hilgard for the explana
ton which he has given of the cause o
the glacial period, and that he deserved
the thanks of biologists throughout tho
world for affording so lucid an exposition
/ in relation to this hitherto vexed question