Evening star., 1951-05-16
Rotating Mirror Used
To Test Speed Of Light
Device Developed at U. of Va.
Is Suspended in Vacuum
By Thomas R. Henry

by inOmoS II. F1enTy
A rotating mirror, magnetically sus-
pended in a vacuum and Whirling at a
rate of 10000 revolutions second, now
Is in operation at the physics laboratory
Of the University of Virginia.
Its ultimate object is to measure
more accurately than ever before the
fundamental constant of all creation.
the speed of light, now estimated at
299, 1925 kilometers per second.
Theoretically this device of DR.. Jesse
w. Beams and j. M. Watkins should be
able to measure light speed to within
one part in 100G0000 although this
probably actually will never be possible
The difficulty lies in the impossibility
of measuring distance with sufficient &C
curacy. There is no way known of
measuring yard within 10 millionth
Of an inch, DR.. Beams says.
The speed of light is the ultimate
speed obtainable. Upon it rests the
major theories of the structure of the
universe. 1t is the basis upon which
the theory of relativity, now generally
accepted, must stand or fall.
One Implication of Theory.
One of the implications of this theory,
as promulgated by Albert Einstein, was
that this speed should remain invariable.
One outcome was classic experiment
in science, the Nicholson Morley ex-
pertinent, one of the most revolution
ary in all modern science. This involved
distance of approximately a mile
With DR.. Beams device it should be
possible to measure light speed with
extreme accuracy over a distance of
few yards in both air and water
The rotating mirror devised in DR..
Beams laboratory is about a quarter Of
a square centimeter in area. For all
practical purposes, it is entirely free Of
friction. The vacuum is as perfect as
can be obtained on EARTH so the fric-
ton with air particles is so slight as
to be immeasurable. There are no con-
tacting parts. due to the magnetic
suspension.
More accurate measurement Of the
speed of light is of tremendous theo-
retical Importance. But there will be
great practical value, DR.. Beams said,
in measuring the speed of many "in-
stantaneous phenomena" which enter
into present-day mechanics, such as
what happens in the course of an ex-
ploSion.
Close to Perpetual Motion.
DR.. Beams and his associates also
have produced a large, magnetically
suspended ultra a-centrifuge which, once
in operation. will continue to revolve at
almost constant speed from so to 100
hours. This is about the closest to per-
petual motion yet attained. AS in the
N1r,iSN fYia SC
although it never can be overcome en-
tirely with any human device. The loss
in this case is somewhat less than two
revolutions second day.
This centrifuge is intended especially
for the extremely accurate measurement
of the weight of heavy chemical mole
cules. It is relatively large, about seven
inches in diameter.
The centrifuge is started revolving by
an air turbine outside the vacuum
chamber in which it is suspended. After
a desired speed of revolution has been
reached, all connections with the tur-
bine are disattached and the rotor coasts
from then On. Reliability is extremely
high.
The centrifuge primarily has been
development of DR.. Beams and his Uni
versity of Virginia associates. 1t has
become of more and more Importance
during the past 20 years for the sepa-
ration of particles of otherwise immeas-
urably different weights. The principle
is much the same as that of the cream
separator.
Last year Dr. Beams and his associ-
ates introduced a modification which
made theoretically possible the weigh
ing of an object within billionth of
gram.