Richmond dispatch. [volume] (Richmond, Va.) 1884-1903, 1897-10-17
MEASURING VELOCITY.
Machine That VIII Photograph In
1OO,OOOth Part of n Second.

The Pittsburg Dispatch announces tina
| Professor Brashear has completed at MI
workshop. in Allegheny. new photo
| chronograph designed for the United
| States Government by Lieutenant Geors'
Squire, stationed at Fortress Monroe, va
The machine is the second one made fol
the government by Professor Brashear
and has many valuable improvements
over the first one, although the main prin-
ciples have not been changed Lieutenant
Squire and DR.. Crehore, one of the IN
ventors, have severely tested the wonder
full apparatus, and II has met all the ex-
pectations of the government experts. IL
is very simple, but is possessed of great
accuracy.
In the present instrument but one single
lever is used to fire the gun, to start the
tuning fork to vibrate, to open the main
shutter and also to release the electric
connections which throw the beam of
light on the Photographic plate. That is'
as soon as the lever is pulled the cannon
Is fired to strike a wire at any point de-
sired This opens the way TO the photo-
graphic plate, which is rotating l,5O revo-
lutions per minute A streak is made on
the Photographic plate, the length OF
which is determined by the rapidly with
which the ball Is moving. as also the
point at which the ball cuts the second
wire, where 1t instantly strikes off the
beam of light.
AS this distance can be readily mea-
sured, the question is to determine how
long the ball is between the two
wires. Before the cannon ball strikes the
first wire in front of the cannon tuning
fork Is set In vibration, and through a
delicate opening in small diaphragm
~ ha NJ timing
a powerful beam of light is sent on TO
the Photographic plate. The vibrations
Of the tuning fork are known exactly, and
as this makes a sinuous stream OF light
alongside of the streak produced ty the
moving cannon ball. It IS only question
of measuring the vibration OF the tuning
fork covered By this streak as also the
fractions of a vibration. In measuring
the fractions of the vibrations OF tuning
fork is where the most delicate work
comes in.
After the Photographic plate Is de-
yeoped 1t is placed under divided cir
Gle and the relations OF the two photo
graphic streaks measured with micro
meter. So exact has this method been
found, that the movement Of hall two
or three inches can readily be timed.
Heretofore measurements OF such short
intervals have been impossible, for the
reason that no Photographic shutter that
had weight could be moved in such
brief space of time. and in this point lies
the beauty of the new invention. Instead
OF moving something that has mass the
light from an electric arc impinSes on
two Nicols prisms. which lie Mt r'gnt
angles to one another. In this position
it is impossible for light to pass through
at all, and IL was DR.. Crehore who dis
covered that if a powerful current OF
electricity be passed through coll placed
between these Nicols prisms the light IT.
self can be rotated without rotating the
prisms. IL can be readily seen that the
electricity acts as shutter, and, as an
electric current has no weight, Ii can be
moved in an incredibly short space OF
time. And even with the lag that ac-
companies all motion, any view lasting
over the one hundred thousandth part
OF a second can be photographed.
The instrument made last year proved
so valuable at Fortress Monroe that the
new machine was ordered for the Sandy
Hook testing grounds. Not only can
the velocity OF cannon balls be deter !
mined between any two points outside |
the lannon's mouth, but IL can be mea-
sured within the cannon. Formerly, any |
attempts In this direction were rather UNI
successful. and the way II was done was
quite destructive to tho gum, as foot |
at time was cut off from the end, so |
as to determine the motion at each point. |
II is only necessary now to place |
stout wooden ramrod against the ball, |
place copper rings around the ramrod, and
make connection with these rings by /
electric brushes at the muzzle OF the gun.