IMPROVED APPARATUS FOR INDICATING THE NUMBER OF REVOLUTIONS OF THE PADDLE WHEELS OR SCREW PROPELLORS OF STEAM VESSELS, APPLICABLE ALSO TO DENOTING THE SPEED OF STEAM ENGINES
Year: 1874

page_text: PROVISIONAL SPECIFICATION left by Henry James Barr at the
Office of the Commissioners of Patents, with his Petition, on the
29th May 1874.
I, HENRY JAMES BARR, of Culter House, near Aberdeen, General in
Her Majesty's Indian Army, do hereby declare the nature of the said
Invention for "IMPROVED APPARATUS FOR INDICATING THE NUMBER OF
REVOLUTIONS OF THE PADDLE WHEELS OR SCREW PROPELLORS OF STEAM VESSELS,
APPLICABLE ALSO TO DENOTING THE SPEED OF STEAM ENGINES," to be as
follows:-
My Invention consists of two dials, the upper is designated the indi-
cator dial and the lower one the clock dial. The latter is carried round
by clockwork worked by a spring and makes one complete revolution in
eight minutes. It is marked off into minutes and half minute spaces.
At each half minute space there are fixed upon the periphery of the dial
metal pins.
Over the clock dial is a metal spring arm which is provided
with a cam working over the metal pins. As the dial revolves the cam
of the metal spring arm in passing the pins is gradually raised until on
reaching the highest part of the cam it is forced down by the spring.

page_text: The lever at its upper extremity carries a piece of slate pencil or chalk,
and this is forced down by a spring and makes a mark upon the dial of
the indicator which is of slate, thus plainly indicating periods of half
minutes upon the indicator. The clockwork may be made to run for
six, twelve, or twenty-four hours each time it is wound up. The
indicator dial is of slate and is mounted in a rim of brass. This rim is
divided into 100 cogs or teeth which are numbered in distinct and
legible characters on the dial from 1 to 100. Close to the upper part of
the brass rim is placed a metal lever escapement, which is worked by a
spring which forces the lever into the teeth of the indicator dial in
succession as they pass over it. This lever is raised out of the teeth of
the dial in the manner to be presently explained. The indicator dial is
revolved by a strong spring in connection with toothed wheelwork,
which carry it round to the extent of one tooth at a time when the lever
escapement is moved. At the upper portion of the indicator dial is
fixed a piece of metal plate, on the inner surface of which is a piece of
moistened sponge and a piece of soft dry cotton cloth. A bottle or other
vessel is provided, and this is filled with water which is conveyed by
filaments of cotton to the sponge to keep it moist. There are two means
by which the lever escapement may be worked; the one is by means of
an electro-magnet; tlie second by direct mechanical connection with
some part of the moving machinery of the engine, such as the rod of the
injector or that of the slide valve. In the former the wires connecting
the electro-magnet with the battery are so arranged that each time the
paddle or screw of the engine to be registered makes one revolution, tho
electric circuit is completed for a moment and the magnet being excited
thereby withdraws the lever and permits the dial to advance in its
rotation to the extent of one tooth. The next revolution of the shaft
allows the dial to advance one more tooth, and so one step by step, such
step indicating one revolution of the paddle or screw. In either case
cach revolution of the shaft of the paddle wheel or of the screw moves
the indicator dial onwards one tooth.
Now supposing the machinery of both dials wound up and the vessel
in motion. The lever of the clock dial will mark on the slate dial of the
indicator cach half minute, and the revolutions of the paddle or screw
shaft will allow the indicator to advance step by step.
Supposing the revolutions to be sixteen per minute, the numbers on
the indicator dial contained between two of the pencil marks made by

page_text: the pencil carried by the lever will be eight, showing eight revolutions
per half minute or sixteen per minute. As soon as the dial bearing the
pencil markings indicating half minutes passes under the moistened
sponge and dry cotton cloth, these marks are obliterated and the dial is
clean and ready to receive the pencil marks anew. The dial of the
indicator will thus show at a glance the number of revolutions made
each half minute for the space of six minutes, and it will do this
continuously.
If necessary an addition to the instrument will enable it with equal
facility and exactness to record the total number of revolutions in twenty-
four hours or any longer period that may be desired. Two of these
indicators will of course be required, one in the engine room for the
engineer, and one on the deck or upon the bridge. That in the engine
room should I think be worked by a direct mechanical connection with
the engine shaft or other part of the machinery. The other on deck by
electricity, but both would make their indications simultaneously. I
estimate the cost of each instrument at about ten pounds at a maximum.
Of course if desired the slate of the machine in the engine room may be
moved simply by hinged arm worked direct from the machinery without
the necessity for the wheelwork and spring, although in the case of the
instrument on deck these would be necessary.
For reading the instrument at night I attach a reflecting lamp such