Evening star. [volume] (Washington, D.C.) 1854-1972, 1910-09-04

margin of load capacity it safely carry The
architect calculate nicely the weight and water
displacement of his iron ships long before the keel is laid
An of few tons might easily make the
But all these weighing achievements simple and
crude compared to the work OF weighing sunbeam,
ray of light, some invisible gas. Scales have been
constructed for this purpose which little short of
magical AT University College, London, there is pair
of scales that will weigh seventhousand millionth of
an ounce These are employed tor weighing invisible
gases and sunbeams and rays OF light. 1t seems
impossible that ray of light should have weight; but
these sensitive scales will demonstrate it.
The scales kept in small underground chamber
made of metal, and the always in semidarkness;
for the light and the heat caused by affect the delicate
beam. The scale beam only few inches long, and is
made OF Silica as glass IS too sensitive to heat to be OF
enters the scaeroom the alteration in the temperature
causes the beam The operator must wait for
hour in total darkness and silence make reading
of the scale. Even when the electric bulb is turned
the sensitive scale feels the vibration of the air caused
by the light The tiny tray of the scale contains glass
tube and into this some imprisoned gas is placed for
weighing In spite of the decacy of the scale and its
wonderful balance the gas weighs SO little that to the
eyes motion of the beam visible but ray OF light
is focused upon mirror and thence upon graduated
scale six feet away The weight of the tube of gas
corded on this scale and the magnifed result easily read
The record may show only thousand mionth
of ounce, the total weight of the Whit OF gas.
Measures of Length
A T the Bureau of Weights and Measures at Sevres.
"A France the standard meter of metal which is the
derground vault and is inspected only at long intervals.
In Great Britain similar exercised in guarding the
standard yard measurement. As II possible for
these metal standards be destroyed damaged the
of time decided number of years ago to de-
termne the length of the standards in lengths
of light which would be basis Of value unalterable and
indesructble. For this purpose the instrument known
the inerferometer invented. This instrument
represented the highest order of workmanship and the
greatest skill of the best opticians of the world series
of refracng plates made, the surfaces OF which
fiat within twentieth of wave length OF light,
with sides parallel within second, representing the
refinement of optical surfaces attempted.
With the interferometer perfected, the attempt was
made to make the wave length of some definite light
actual and practical standard of length For year
scientists worked to this result and experiments
finally showed that there 553 wave lengths of
red cadmium light in the French standard meter, at fiji
teen degrees cengrade So great the accuracy OF these
experiments that they can be repeated within part in
two millions. Soinconceivaby small is such possibility
of that should the material standard of length be
damaged destroyed the standard wave length of light
would remain unaltered basis from which exact
duplicate of the original standard could be made.
Scientific Clocks
SOME of the greatest renemens of mechanical science
- have been made in the division and the measure
ment Of time, and the delicate instruments employed