Evening star., 1936-01-14
STARS, MEN AND ATOMS
Notebook of Science Progress in Field,
Laboratory and Study.
BY THOMAS r. HENRY

A walking machine has been con-
structed and now is being tested at the
Bureau of Standards.
1t is designed to determine the wear
ing qualities of shoe leather in actual
use. The machine was designed to imi-
tate. to some extent, the forces which
are applied to a shoe in service Motion
pictures of persons walking were ana
lyzed and served as a guide in working
out the motions of the different parts
of the foot.
This walking machine, designed by E.
L. Wallace of the leather section. con-
siSts of eight radial cylinders having
pistons ground to fit smoothly. These
cylinders and their projecting pistons
form. in effect, the spokes of a rimless
wheel, and the whole is free to rotate
about an axis. Four pairs of Shoes fitted
to plastic rubber forms, are fastened to
the movable pistons by adjustable hinged
joints.
The load applied to each shoe is con-
trolled by an adjustable compression
spring within the cylinder. An endless
belt is driven across a bed of rollers by
a motor and the radial cylinders are
caused to rotate by contact of the shoes
on the belt surface.
The load on the shoe gradually in
creases and is at a maximum when the
piston is perpendicular to the belt sur
face. AS the shoe travels farther, the
load gradually decreases. the heel leaves
the belt and the toe is f1exed somewhat
as in walking. The shoes are run against
rubber belt to minimize any wear on
the soles, since the test primarily is in
tended to show comparative endurance
of the upper leather, Innings, stitches
and heels.
Preliminary tests now are being run on
tn, machine, and thus far the results
check closely with those obtaining In
actual walking. However rigidly de-
termined are the physical and chemical
properties Of leather. says the Bureau of
Standards account of the device, they are
of little moment compared with the
actual service test.
After more than II years work, Bu-
reau of Standards physicists have ar
rived at an absolute determination of
the ohm, the standard unit of electrical
resistance which is employed univer-
sally wherever electrical measurements
are made.
The internationally accepted standard
for the ohm is "the resistance offered to
an unvarying electric current by the COL
umn of mercury at the temperature of
melting ice, 14.4521 grams in mass, of a
constant cross-sectional area and of a
length of 106300 centimeters." More
practically, 1t is defined as the resistance
offered by 400 feet of common telegraph
wire.
At the Bureau of Standards it is de-
termined more precisely by coils of wire
which are so constructed that their re-
sistance is expected to remain constant.
The physicists long have recognized,
however, that the measurements were
not absolutely constant and that they
did not completely coincide with the
theoretical ohm as measured in the mer-
curry column, method which Is i'm
practical in actual use.
There were two highly important
reasons for making an absolute deter
mination of the ohm" says a Bureau OF
Standards report on the long investiga-
ton. I'm the first place it was essential
that the unit should correspond as closely
as possible to the fundamental dennitlon.
There are always errors In any expert
mental investigation, so that 1t Is never
possible to be certain that the actual unit
exactly corresponds to the theoretical
one. The present practical unit depends
on absolute measurements made more
than 10 years ago. During this time
there have been important improve
ments. both In materials available for
the construction of suitable apparatus
and IN measuring technique.
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