The New York herald., 1922-03-10

signed. as some leakage of the gas is
probable. Lord Rayleigh finds that, In
general, ages OF about one-third those
from estimates OF lead are obtained.
Professor Sollas pointed out the neces-
sity of making sure that the radioactive
clock was not as much too fast as
Lord Kelvin's was too slow. He drew
attention to the phenomenon of pleo-
chroic halos occurring in uranium bear
ing black mica. These halos. which
have been studied by Professor Jolly, are
formed by the X-rays expelled by ura-
MUM in the course of its disintegration.
In general the ranges OF the rays are
consistent with those found at the pres
ent time. In the case of the two inner
rings however. the ranges are greater
than normal and Professor Jolly has con-
cluded from this that in Caledonian times
there existed metope of the uranium
we now know with different properties.
IL this conclusion is correct the radium
clock has not been keeping uniform time
and estimates OF the age of the earth
which are based upon it are liable to an
error of an uncertain amount.
Professor Gregory dealt with the geo.
logical estimate OF the age of the earth
based upon the salinity OF the sea. Es-
Inmates obtained in this way varied from
seventy to one hundred and fifty million
years. He pointed out that the argu-
ment suffered from three fundamental
objections. 1t was assumed that the
sea was originally fresh. although the
oldest fauna, the Cambrian, had marine
characteristics, and the contrast be-
tween the fresh water and marine fauna
In PaIaozoic times was as sharp as II
is to-day. There was also no allowance
Tor the large supplies of sodium chloride
raised from beneath the earth's surface
by magmatic waters.
Further, a uniform rate OF denudation
was postulated. whereas there have been
alternating periods of quick and slow
crustal movements: the earth is now
under the influence of time OF quick
movement with, consequently. dcnuda-
ton faster than the average. Taking
these three causes separately Professor
Gregory estimated that TO allow for
them the age of the earth deduced from
the salinity argument should be multi
piled two fold, three or four fold and Ave
fold respectively. lie concluded by stat
ing that the best known geological esti-
mates of the age of the earth require TO
be multiplied ten or twenty fold in
order 10 agree with the physical csti-
mates and that this increase is consist
ent with the geological evidence. on
the other hand, Professor Sollas dis
sented from this view and was not pre-
pared to accept such an increase.
DR.. Jeffreys stated that from consid-
eratons of the temperature distribution
downward I'm the earth's crust, allowing
for the radioactive content. and also
from the tidal theory of tho origin OF
the solar system, he had separately de-
rived concordant estimates OF about
two thousand million years since the
solidification OF the carths crust. Thus,
with revised data. two Of Lord Kelvin's
methods OF reasoning have been brought
into agreement with the results derived
from other physical methods.
II will have been gathered that. on
the whole, there Is now a satisfactory
agrccmept between the results OF argu-
ments based upon astronomical, physical
and geological considerations. These
arguments combine in indicating an age
OF the earth. since soiidifcation, OF about
one thousand million years.