New-York tribune., 1910-09-04


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margin of load capacity safely carry The marine
architect must calculate nicely the weight and water
displacement of his iron ships long before the keel is d
An error of few tons might easily make the shpafalure
But all these weighing achievements are simple and
crude compared to the work of weighing a sunbeam
raw of light or invisible gas. Scales nave oeen
constructed for this purpose when are niue soft vi
magical At University College, London, there is palr
of scales that will weigh seven thousand mlllonth OF
an ounce These are employed for weighing invisible
gases and even sunbeams and rays of light 1T seems
impossible that raw of light should have weight; but
these sensitive scales will demonstrate It.
The scales are kept in small underground chamDer
made of metal and the room IS always IN
for the light and the heat caused by it affect the delicate
beam. The scale beam is only few inches long ana IS
made of Silica glass too sensitive to heat to De OF
use It is a mere cobWeb-like machine, and When one
enters the scaleroom the alteration in the temperature
causes the beam to The operator must walt LOT
an hour in total darkness and silence to make reading
of the scale Even when the electric bulb IS turned on
the sensitive scale feels the vibration OF the AR caused
by the light The tiny tray of the scale contains glass
tube and into this imprisoned gas IS placed lot
weighing In spite of the delicacy OF the scale and Its
wonderful balance the gas weighs little that to the
eyes motion of the beam is visible but ray OF hight
is focused upon mirror and thence upon graduated
scale six feet away The weight of the tube OF gas IS re-
corded this scale and the magnifed result easily read
The record may show only thousand 1nlionth
of an ounce, the total weight of the Whit OF gas
Measures of Length
A T the Bureau of Weights and Measures at Sevres,
France the standard meter of metal, which IS the
standard length of the world is kept carefully in an un
deground vault and inspected only at long intervals
In Great Britain similar exercised IN guarding the
standard ward measurement As 1t was possible tor
these standards to be destroyed damaged IN the
course of time decided number of years ago to de-
termne the length of the standards IN wave lengths
of light which would be basis of value unaterable and
indestructibe. For this purpose the instrument known
as the nterferometer invented. This instrument
represented the highest order of workmanship and the
greatest skill of the best opticians of the world series
of refractng plates made the surfaces OF which
were fiat within onetwenteth of length OF light.
with sides parallel within second representing the
refinement of optical surfaces ever attempted
With the interferOmeter perfected the attempt was
made make the length of some definite light an
actual and practical standard of length For year
scientists worked this result and experiments
finally showed that there 553 164 wave lengths OF
red cadmium light in the French standard meter at hf-
degrees centgrade So great the OF these
experiments that they can be repeated within part IN
millions. So nconcevaby 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
COME of the greatest refnements of mechanical science
~ have been made in the division and the measure
nent of time and the delicate instruments employed