The New York herald., 1922-12-10


~ DR.. b. w, Aston, r. h.
II an ordinary evacuated electric
light bulb were pierced with an aper-
ture such that one million molecules
of the air entered a second. the pres
sure In the bulb would not rise to that
Of the air outside for a hundred million
years. Perhaps the most striking illua-
tration IL as follows: Take tunbler Of
water and-supposing It possible-labeI
all the molecules In II. Throw the
water into the sea. or. indeed. anywhere
you please, and after a period of time
so great that all, the water on the earth
lin seas. lakes. rivers and clouds-has
had time to become perfectly mixed. I'LL
your tumbler again at the nearest tap.
How many OF the labeled molecules are
to be expected in itf- The answer Is.
roughly. 1000; for although the num-
ber Of tumblerfuls Of water on the earth
is 6x1on. the number Of molecules Of
water In a. single tumbler u 10s'.
From the above statements 1t would.
at first sight. appear absurd to hope to
obtain effects. from single atoms. yet
this can now. be done in several ways.
and indeed 1t is largely due to the re-
suits of such experiments that the fig-
ures can By stated with SO much cohflr
dence, Detection Of an Individual Is
only feasible in the case Of an atom
moving with an enormous velocity when.
although Its mass Is so nslnute, its en-
ergy Is quite appreciable.s The charged
helium atom shot out by radioactive
u,,hsto xc~~ a., tho Fcrv, ~ ~ olrho ra u
possesses 80 much energy that the splash
Of light caused by. its impact against 2
fiuorescent screen can be visihly de-
tected. the ionization caused by Its pas
sage through. suitable gas can be
measured on a. sensitive eiectrometer,
and. in the beautiful experiments Of G..
T. r. Wilson, its path in air can be- seen
and photographed by means Of the con-
densation OF water drops upon the
atomic wreckage 1t leaves behind IT, :.
The first experimental comparison cf
the weights Of Individual atoms was
made by Sir j. ]. Thomson In his analy-
sis OF positive rays by the "parabolar
method. Subjected to this test most OF
the lighter elements appeared to follow
Dalton's rule, but the results with the
rare gas neon suggested the possibility
Of the atoms Of this element being OF
two different weights, roughly 20 and
% respectively. > In other words the
parabolas Of neon indicated that It
might be q mixture of isotopes. but the
accuracy of measurement by this
method was not sufficient to settle the
point with certainty.
The requisite accuracy has been OBJ
tained by an instrument for the analysis
of positive rays called the 'cass spec
trograph." BY this device the weights
of atoms can be compared to an accu-
racy Of one-tenth per cent, and 1t has
been demonstrated not only that neon
(202) Is q mixture Of atoms Of weights
exactly 20 and %. but also that chlo-
rine (s5.4e) Is mixture Of isotopic
atoms of weights IS and 81. Further
more, about half the elementS investi-
gated turn out to be mixtures. some OF
the heavier ones consisting Of six or
more different constituents. Most Inn
portant Of all Is the fact that every ele-
ment investigated. with the exception OF
hydrogen. consists Of atoms tho weights OF
which are expressibfe as whole numbers
on the oxygen scale used by chemists.
This remarkable generalization called
the whole number rule" has removed the
last obstacle In the way Of the unitary
theory OF matter. We now have no hes
itation in affirming that nature uses
the same standard bricks In the con-
struction Of the atoms Of all elements
and that these standard bricks are the
primordial atoms Of positive and mega
tive electricity. protons and electrons.
These are the natural unit charges OF
electricity. equal but Of opposite sign.
OF the shape of these particles we know
next to nothing. but the wonderful ad-
vances Of modern physics. In particular
those Of radioactivity. enable US to speak
Of their weights and dimensions with
some assurance. The weight OF the
proton IL very nearly the weight OF a
hydrogen atom, the electron IL nearly
two thousand times lighter. 80 that the
atomic weight Of an element (not con-
sixtins Of isotopes) will be roughly
equal to the number Of protons In Its
atomA.
We now know of what atoms are con-
structed, and may go on to consider the
evidences az to how their constituent
parts arc arranged. We're we to con-
struct a scale model Of the atom as