Evening star. [volume] (Washington, D.C.) 1854-1972, 1935-03-03

in my hand - and it seemed over-Optimistic
to expect such toy-like thing to tell anything
important about the stresses which the
hundred times larger wall of concrete would
be called on to endure.
But the researchers have ways to get
around the obvious. In this Columbia labor
atory is an ingenious whirling machine. 1t can
multiply load 3 900 times - that is, increase
the weight" of pound to ton and half!
When the model was placed in this apparatus
and whirled, centrifugal forces were generated
which made the toy load of sand press against
the toy wall with force directly proportional
to that of gravitation. A flashing light illu-
minated the model for an instant at each
revolution, enabling fast camera to photo
graph the behavior of the wall under the
strain - and the weak spots were glaringly
revealed.
1t would be more direct, of course to test
the concrete wall itself, full size, under the
natural conditions of its site But this would
cost thousands of dollars and months of time,
and would eat up in advance any possible
saving. The small model costs few dollars
only, it can be set up within few hours, and
by applying the mathematical law of simil-
itude the critical facts about the wall can be
learned as accurately from the toy as from the
full-scale structure. As result of this dis
covery, whole Laboratories are given over to
the fascinating pursuit of tinkering with
marvelously exact scientific toys.
-- At the governments Waterways Expert
ment Station on the Mississippi near ViCks-
burg. for example, is l4O-acre tract on which
every dangerous curve and contour of the
Mississippi river has been worked out in
miniature. Recently, as a result of these
studies with toy river. seven bends in the
Mississippi were cut through. shortening the
stream by seventy miles and simplifying the
problem of flood control.
Before the first concrete for Boulder Dam
was poured, the whole project had been tried
out in plaster models at the laboratory of the
Bureau Of Reclamation in Colorado Mercury
was used to simulate water in the miniature
dam. Similar studies guided the Norris Dam
engineering in the Tennessee Valley.
A unique tower construction has been
adopted for the San Francisco Bridge now
being built across the Golden Gate. This
innovation was perfected through tests of
steel models, performed at Princeton Univer-
sity and at the University of California The
Port Authority of New York used brass as the
material for model Of the span of its Bayonne
Bridge; and by means of this model learned
the economy of using less expensive steel
than had been thought necessary
At Cambridge, Mass, is a shaking platform
geared to make motions like an earthquake
This jigger grew out of certain experiences in
California in 1893, when a quake put many
elevated water tanks out of use, seriously
crippling fire protection. So group of fire
insurance companies began to ask questions.
Are elevated tanks peculiarly vulnerable to
earthquake shocks1 What structural type will
stand most securely They turned to the
Massachusetts, Institute of Technology with
these questions II and the answer is being
sought from tank models on that shaking
platform. Already these studies have demon
strated that some OF the forms which have
been designed to add strength to structure
are in reality sources Of weakness under earth
quake conditions.
Architects are using models to try out
preliminary plans. When the new laboratory
building of the Mellon Institute in Pittsburgh
was projected few years ago. fou-foot-
high model of the proposed nine-story building
was erected. Certain changes resulted. and
then nineteen-foot model showed the design
in larger scale. Now full-size model of a
corner of the building and full-size models of
two typical laboratory rooms have been
erected for detailed studies of arrangement,
furniture and service features. Altogether
$4,000 was spent on these models - but
results justified it, say the engineers.
One of the current ingenuities of the experts
is to make the toy model out of glass. cellu-
lOid bakelite or some other fransnarent