Evening star., 1937-12-07
impossible Jobs Done in Jiffy
At Bureau of Standards ShO,u
200, 600, ,OOO, ,OOO, 900 Grains of Cement IL,
Bag Counted as a Routine Task at
Exhibition of Methods.
requirements for different sorts Of

requirements for different sorts OF
jobs.
Another thing Mr. Tucker revealed
is that tamping Of cement is old-fash-
ioned. Nowadays it is hammered
down into solid mass by vibrations"
which shake the particles into place,
and one of the really outstanding de-
velopments Of the year is vibration
measurer. BY means of this instru-
ment. developed by George Pigman
and Floyd Hornibrook of the Bureau
staff, it is possible to measure at any
point at any time in concrete job
the amplitude. velocity and accelera-
tion Of the vibrations which are being
sent through the mass of cement. The
development may be of extreme i'm
portance for cement structures by de-
tecting weak spots which are not being
sufficiently vibrated.
From the cement laboratory the in
quisitive reporter walked across the
way to the room where c. G. Peters
was showing members of the Bureau
staff how to make measurement Of
2000, 900 000ths of an inch. That is
the most precise measurement which
can be made with much confidence.
When the laboratory staff try to make
a finer determination a slight error
may creep in.
Light Wave Utilized.
Obviously one doesn't measure In
billionths of inches by footrule, or
any other measuring device made by
man. The measuring rod is wave
length Of red light obtained by
making luminous the rare element
cadmium. 1t now is the accepted
standard the world over. This is
about .00003 of an inch in length.
Where two objects to be compared
differ from each other by more than
this, the disparity is apparent from
the interference fringes shown by
device known as the interferometer.
Then other wave-length of light. of
known length, are used to get finer
and finer distinctions.
Altogether this is probably the
most delicate piece of measuring ever
done in the world and the Bureau
of Standards looks upon it as one of
its major achievements. 1t is so
fine. in fact, that up to date there is
little practical use for it. About
millionth of an inch is good enough
for industry but If it was not possible
to measure as delicately as this some
Of the most marvellous mechanisms
of the age would be impossible.
Egg Spins EndIessIy.
And a few doors away-just to
amuse the children, it was explained
was fellow who was going Columbus
about 10 better. He not only. was
making an egg stand on its small
end but was making it spin around
endlessly in that position, like top.
The egg, made of metal, was placed
in a .wcoden bowl which in turn was
placed over two coils through which
passed an alternating, two-phase cur
rent. The egg was set in rotation by
currents induced in it's own shell
and once the rotation grew fast
enough it stood naturally on its
small end.
The trick was arranged to illustrate
principle of considerable importance
in testing the master meters in the
possession of power companies, with
which they in turn calibrate meters
in the houses of their customers.
Beside it was another electrical device
by means of which quarter inch rod
of iron was melted in Is seconds.
The exhibit last night was held for
members of the Bureau of Standards
staff and their families. 1t will be
repeated tomorrow night for a group
of specially invited guests.