Semi-weekly herald., 1911-04-10
many cunning little devices for max
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ng her children comfortable


Nearly sSseery rgreat1 na94ioa power
maintains within-so of its ship
building plantsrrnr navy yards a toy
ocean. upon which miniature models
tDf laval vessels are launched and op-
Grated in order to determine whether
certain details of construction have
been carried out correctE', says Har-s
per's Weekly dfs7b aGiissuga4a .t
+ This idea had its inception in the
mind of ,Froude, the British naval CON-
lstructer, something over a quarter of
n century ago. He performed a. Sc
ries of experiments with scale models
designed to predetermine the resist
ance of ships about to be built for the
navy. He made small models of r,he
vessels to be constructed, giving great ii
l;care to the preservation of the scale; ;ul
and these models he then towed Y
Through the water under varying con-
ditions, by mechanism extremely SER
Isitive to variation in tho pub. The
tension in each case was carefully re- ~
corded, and conclusions were drawn as =
| to the lines most favorable for speed 2;
To. verifyshis results Rritish man *
of-war was towed by another vessel
and the. actual pull on he tow-rope
was. carefully measured and com,,ared
with the results of the experiments
made with small model. The two
sets of answers were so nearly alike
as to leave no doubt of the practica-
bility of actual experiments with re-
duced scale models. t.ff4.t..s adf .,4
The United States government pos
sesses such a model basin for expert
ments of this kind u. the Was!,sig-
ton navy, yard. Within q building de-
signed to protect it from ail disturb.
ing conditions Of the atmosphere is
tank of pure, fresh, water, almost 400
feet long and having depth of some
fourteen feet, Spanning, this narrow
sheet of water is movable bridge,
set upon steel rails, which run paral-
lei to the length of the BASIN, Heay-
lily built and fastened and braced so 5
tightly as to, avoid all unnecessary
vibration, this bridge is provided with
a powerful motor, which can drive it
along the rails, if need be, at rate
of twenty knots or more per hour.
The model of the proposed ship,
cut from soft-pine and ballasted with
the utmost care, is firmly fastened to
ar arm projecting from below the CEN.
ter of the bridge, or towing carriage,
Tas it is called. One the carriage are
placed the delicate dynamometrical
mechanisms that record the pull" of
the model as it glides through the
water beneath the span Of the. bridge.
This, multiplied by the proper guam
tity, must establish accurately the
power that will be required to over
come the resistance of the finished
vessel. By reason of an almost flaw
less electrical adjustment, the bridges
moves forward with an even motion,
without trace of rattle or jar. e.t
In addition to the motormen, there
are two persons on the carriage dur
ing an experiment They watch the
pens of the recording cylinder of the
ldynamometer. uoo.. sbiy ft,...t
When everything is ready for an
experiment, the bridge, at the clang OF
a gong, starts from the south to the
north end of the tank while beneath
il the model of the warship glides
evenly through the. water. AS the run
nears its end, and one wonders how
the bridge with its. delicate instru-
ment is going to avoid collision with Al,
the wall ahead, two great hydraulic
brakes operate automatically and
bring the mass to a gentle stop with
out jar or culver. aoja i1loN sdi
-IlanL Innn II. mimi ..at L..,.......tr.-