The Indianapolis journal. [volume] (Indianapolis [Ind.]) 1867-1904, 1897-05-09

and even to the mortar dispfoves the idea
that they may have existed In the stone
before use for building. Cracks down the
walls. moreover, are visible marks that the
lightning seems to have left in some cases.
The ordinary electric spark, in a length
ened form a synonym for inconceivable
rapidity, is too slow for modern require
ments. In his attempts to photograph fly
ing bullets by the light Of the spark Prof.
c. Vernon Boys found that the double flash
produced lasted somewhat less than the
lOO,VVOth or q second, giving only blurred
pictures. He therefore shortened the
spark. Instead of wire terminals, ne used
two very thick. broad bands of copper not
more tina two inches long, which reached
round opposite edges of the Photographic
plate in such a manner that a spark re-
suited when electric junction was effected
by the passage of the bullet. The spark
was thus shortened to about 1-13,OV0.O OOth
of a second. In this time a bullet from
an ordinary magazine fifie could not traVel
more than 1-500th of an inch, and good ana
sharp pictures were obtained.
The latest determination of the limits of
addition, according to Lord Rayleigh, gives
twenty-four complete vibrations a second
for the lower limit and about twenty thou
sand for the upper. Both limits, however,
are i'll defined, depending largely on the
vigor of the vibration and the individual.
Experiments seems to show hat q Vlora-
ton having an amplitude of only S-lO0, OOO,O00
of a centimeter can still affect the ear,
such a vibration being one hundred times
smaller than the smallest object Visible
in any possible microscope; or, stated in
another way, the ear is so sensitive that 1t
distinguishes differences of pressure one
hundred times less than the residual pres
sure of the best VacuumS, which is meas
ured in millionths or less of an atmoS-
phere. The propagation of strong sounds
is doubtless greatly hindered by atmoS-
pheric refraction. This would seem to eX-
plain why some sixty-horse-power Trinity
House sirens can scarcely be heard two
miles away, although calculation from the
law of inverse squares would seem to prove
that the sound should travel 1,50O miles.
In the perception of pitch a good observer
can distinguish a difference of only a third
of q vibration per second. This is when
sounded simultaneously, there is scarcely
any limits TO the minuteness of difference
revealed by the beats. The feeblest grave
sound, with a remarkable power OF obit-
Grating and masking q high one, is able to
make itself heard very s~trikingly in spite
of high ones.
In his tests of the Turbinia, the first YES
sci using the compound steam turbine, the
Hon. Chas. A. Parsons has experienced the
not wholly unforeseen difficulty of ex-
cessiVe speed of the screws. The effect of
this was shown by an ingenious expert
ment. Model screws We're revolved in a
bath of hot water, a revolving mirror on the
screw shaft rejecting the light of an cleo
trio arc to the screw at one point only, and
thus causing the shape and growth of the
cavities to appear as plainly as if station
airy. A cavity or blister first formed a lit
tie behind the leading edge and near the
tip of the blade. AS the speed of revolu-
ton increased this cavity enlarged in all
directions, until, at a speed corresponding
to that of the Turbinia's propeller, it COW
cred a sector of the screws disk of 80
degrees, and at q little higher speed nearly
the whole energy of the screw was eX-
pended in maintaining a vacuous space.
The turbine ultimately used is of the three
stage compound Order, each expansion haV-
Ing us separate motor WORKING It's OWn
propeller shaft. The vessel, which is one
hundred feet long. nine feet beam and for
ty-four and one-half tons displacement, has
exceeded thirty-one knots, the energy de-
veloped being 1876 indicated horsepower,
with a steam consumption Of 1886 pounds
per HORSEPOWER hour. The total weight
The results seem to be Unprecedented for
a vessel of the size, although it is recog-
niZed that Improvement of motor and re-
duction of revolutions are necessary to
make the system practicable.