The Washington times. [volume] (Washington [D.C.]) 1902-1939, 1922-02-13
WEIGHING SUNLIGHT
DO LIGHT RAYS WEIGH ANYTHING?
Prof. Serviss Says 1t Has Been Shown TheO-
retically and Experimentally That
Light Exerts Pressure.

gravitation. He preoicteo Inc
bending Of the rays Of light,
phenomenon that most persons
today suppose to have been dis
covered by Einstein. All that
Einstein has done Is to approach
the subject in a new way, MADE
possible by the advance OF scien-
tific knowledge since Newtons
day.
And now mark how science
sometimes pauses, and goes back
a little way along her path, picks
up something thet she had drop
ped, examines it with freshened
attention, and discovers aim Sst
a new world of knowledge in II.
No doubt she has unwittingly
thrown away many diamonds
that she will never recover. One
of the latest returns on her track
that science has made Is now in
the very act. Nobody knows
vet all that may result from 1t,
but one very notable thing is that
II has already restored, In a GER
tain sense, Newton's original idea
that light Is made up Of some
kind of protectiles shot out from
shining bodies.
They now call these ''quanta.
There is still a great deal of the
enigmatic about them, and we
need not consider them futher, ex-
cept to point out that a projectile
of any kind, necessarily implies
the possession of mass, and mass
cannot exist in the presence OF
gravitation without manifesting
what we call weight.
The streams Of projectiles, or
auanta, that forms light rays, must
be drawn out of their course by
the gravational force of the earth,
the sun, and every other massive
body. But they go SO fast-le6.OOO
miles in a second-that ordinarily
they get past, and practically out
of the reach Of the attracting body
before a noticeable DETECTION has
occurred in their direction. II re-
quires a body of great mass and
size, like the sun, to affect a pass
ing light ray with sufficient in
tensity, and for a sufficient length
of time, TO IT, n IL so much aside
that our means Of observation may
detect and measure the wandering.
This is the lever that lifted Elm
stein into popular fame. He pre-
dicted. as Newton had virtually
done long ago. that II would be
found that a ray of light from a
star passing close to the sun was
bent a little by the suns "gravi-
rational field The uninitiated
might suppose that any astrono-
mer could try that experiment any
day. But not so; the experiment
requires very exceptional condi-
tons which are very rarely met
with.
To mention only one thing-the
sun must be hidden from the OBJ
servers eyes in order that the
star lying nearly behind ii may be
seen, and this can only happen
during a total eclipse Of the sun
by the moon. Moreover, the sun
must happen at the moment to be
very nearly in line with some star,
or several stars, bright enough to
be easily seen in the semi-obscur.
ity of an eclipse.
These conditions were met IN
the eclipse of May 90. 1919, ard,
being then for the first time actu-
ally looked for, then for the first
time the bending of a ray of star
light in passing the sun was OBJ
served and measured. The light
was DETECTED one-and-three-quar-
ter seconds Of arc from it's nor
NAL course, the amount agreeing
with Einstein's prediction. And so
we have got to the door Of Elm
STEMS lodge without having en-
countered any Of the errors Of his
wilderness.
Here, then. you have visual
proof that light weighs some
thing" just as a long distance
shell, a wing on it's way of destruc-
ton through the high air, gives
visual proof Of its weight by curv-
ing gradually downward toward
the attracting earth. But there is.
and has been, other proof no less
satisfactory.
1t has been shown. both theorat-
ically and eXperimentally, that
light exerts pressure. 1t cannot
do that unless il has momentum,
and it cannot have momentum nm
less IL possess mass, and, Conse-
uuently, in the presence of a grav
itating body. weight. Your very
act of seeing is a proof of the
weight Of light, for the nervous
structure OF your eye is so con-
trived that the impact Of the light
on the retina is transformed in
your brain into the sensation OF
vision. as the hammering strokes
Of air-waves on the ear drum make
the senSa ton of sound.
A. S. Eddington has calculated
the weight of light. "All the sun
light falling on the earth" he
says, amounts to 100 tons daily"