The sun. [volume] (New York [N.Y.]) 1833-1916, 1882-12-17

equatorial regions. anu consequently bn oA-
traordinary supply OF tho raw material OF
snow in the temperate regions. But how
arc We to account for tho vast accession
of hoat which would havo been required
to lift from seas and rivers a quantity
OF water corresponding to the magnitude Of
the leo sheets which. according to the glacier
ists covered tho continents during the drift
agop None Of tho conjecturcs which would
give II subterranean origin to tho great increase
Of heat which followed the tertiary era. and
preceded the ice ago. arc satisfactory. Pref
Frankland. for example. thought that the ocean
might have been rendered hot by tho internal
fires of the earth and thus the water sent up
in clouds to fall in ice and snow. But Sir John
Lubbock refutcd this theory by showing that
the fauna of the seas during the glacial period
possessed an Arctic character
What. then. according to Mr.. Donnolly. are
the elements OF the problem presented by the
phenomena of the drift age2 First. we are to
find something that instantanoously increased
to vast oxtcnt the heat of our planet. vapor-
lied in large degree the seas, and furnished
material for delugcs Of rain. great storms Of
snow. and accumulations of ice north and
south of the equator aud In the high noun
| tains We are to find something also That
brought to wide areas of the earths surface
incalculable masses of clay and gravel. contain
ing mono OF the earths fossils. and marked
after fashion not exhibited elsewhere on earth.
The agency to be discovered mus. .urtner be
one that wvuin Produce cyclonic commissions
upon q scale for which the ordinary operations
Of nature afford no parallel Would comet
meet all these prerequisites? 1t is the object
| of this book to answer the question in the af-
| frmative.
According to the received opinions among
astronomers comets consist OF a blazing nu-
cleus and a mass Of ponderablo separated mat
ter. which grows more and more attenuated
and transparent toward the end OF the comets
tail. The material OF the trailing appendage ar
ranges itself in regular order. the largest frag-
ments being on or nearest the head the smaller
| further away diminishing in regular graduation
until the extremity consists of dust and gases.
There is continual movement of the PARTICLES
| Of the comets trail. caused by the laws
of attraction. The fragments collide and
crash against each other. each stone so
placing itself in conformity with a natural
law chat its longest. diameter comedies with
| the direction OF the motion Of tho planet :
hence. as these stones scrape against each
other they mark each other with lines
or strie Tho fine dust ground out
by these perpetual collisions does not
TO Off into space. but, still governed by the at
traction of the head. falls to the rear, and takos
its place ut the end OF the comets tail. Ii is to
this comet dust that Mr.. Donnely would trace
the origin of the drift clays. for clay. we are
minded. is II finely lovigated earth. formed by
the disintegration of feidspathic or granite
rocks. Now. ON the surface Of our globe gran
ito is found only in limited areas. altogether
inadequate to produce by leyigation or erosion
the masses Of drift clays which cover CONT
ncnts to a depth OF hundreds of feet. More
over it is observed that no such clays are being
now formed under glaciers and Arctic ice
sheets. SO much for the cays which form the
greatest portion of the drift Mr.. Donncly
further argues that 1t is to comet We must
look for the source Of great part Of the do
posit of gravel. pebbles and stones found In
the drift because the earth supplies of
gravel are insufficient to account for such de-
posits. and because neither sea beaches nor
rivers produce stones shaped and marked like
those found in the drift.
Assuming the correctness Of Mr.. Donnel-
lys hypothesis. that the drift deposits
were made by a comet, in what circum-
stances are We to suppose that the col
lison between the comet and our earth took
place? The authors conjecture is that great
comet like that Of 1913. approached close to
the sun, as was the case in the year mentioned
and swung through q great arc its mighty
tail more than a hundred millions OF miles in
ength. moving. too. at rate almost equal to
the velocity OF light. and swept past the earth
the earth as 1t were. plunging like bullet
through the midst of the tail. which would ex-
tend for a vast distance beyond and around it.
In this movement tho side OF the earth facing
the advance Of the tail would intercept the
mass Of materiai-sones, gravel. and the
finely ground dust that. compacted by
water is now cay-which came in contact with
il. while the comet would sail Off into snace.
disodged. perhaps. in some degree from its
orbit like Ipypll'S comet when il became n
tangled with Jupiter's moons. but shorn Of
only comparatively small portion OF its sub
stance. We should bear in mind. in consider
ing this hypothesis, that the great comet Of
1s43 whose head is believed to have actually
grazed the surface of the sun. possessed a tail
100000 600 miles long-a TAIL that is. which
would reach from the sun to the earth and have
over 80. 000, 900 miles to spare. Again. the tail
Of the great comet Of 1871 was 1l6 900. 900 miles
long. and nearly l4,00o,o00 miles broad at its
widest part, Conceive, says Mr.. Donncly, such
Il comet as the last named rushing with awful
velocity past this earth of ours. whose insig
nincant diameter falls short of 5000 miles
The earth would simply make bullet hole an
cyelet hole. pin hole through the comets
tail 14O000 900 miles broad. And yet in that
moment Of contact the side OF the earth facing
the comet might be covered with hundreds Of
icet Of debris.
1t may be objected that the dense masses Of
clay and gravel composing the drift could not
have fallen from comet because the tails Of
comets are composed of material so attenuated
that sometimes the stars are seen through them
Mr.. Donnclly reons that although the particles
of dust composing the tail had been as minute
as those Of clay dust and although they had
been separated from each other bya distance Of
many feet, they would still-if we supposed the
tail to have been as broad as that of the comet
Of lSll-have left deposit on tho face Of any
object passing through them much greater
than the drift. The author demonstrates the
truth Of his assertion in this wise. You ride.
on o summers day. n hundred miles in rail
road car seated by an open window. There is
no dust pcrccptib!e. yet at the end Of the jour-
ney you find yourself covered with an unmis-
taxable coating Of dust Now, suppose that
instead OF travelling 100 miles. our ride had
been prolonged for IA 600 900 miles. and that.
instead of tho atmosphere being perfectly clear.
We had moved through q cloud OF dust not
dense enough. indeed. to intercept the light of
the stars, and yet dense enough to reflect the
light of the sun. In such case we can hardly
/ doubt that long before we had reached the end