AN IMPROVED RANGEFINDER FOR ASCERTAINING DISTANCES AT SEA OR ON LAND
Year: 1882

page_text: LETTERS PATENT to George William Hart, of 22, Ordnance Row, Portsea,
in the County of Hants, for an Invention of "AN IMPROVED RANGEFINDER
FOR ASCERTAINING DISTANCES AT SEA OR ON LAND."
PROVISIONAL SPECIFICATION left by the said George William Hart at the
Office of the Commissioners of Patents on the 17th January 1882.
GEORGE WILLIAM HART of 22 Ordnance Row, Portsea in the County of Hants.
"AN IMPROVED RANGEFINDER FOR ASCERTAINING DISTANCES AT SEA OR ON
LAND."
I provide a bed, or base-plate of any suitable metal, divided into degrees minutes
and seconds, and which bed or base-plate can be rotated upon a vertical axis.
Upon this base-plate I mount two telescopes one of which is fixed, and the other
moveable, and between these telescopes I fix an index-plate to shew when the
telescopes are parallel, or the relative amount of their convergence, or divergence.
The motion of the moveable telescope is effected by a drum affixed to a tangent
screw which gears into a wheel, upon which wheel is fixed the above mentioned
index-plate. This drum is covered except in line with the
or zero of a
vernier, and upon said drum a succession of figures appears, as said drum is
revolved to move the moveable telescope. These figures indicate distances which
are read off by the observer, and the figures which appear under the number on
the cover corresponding to that shewn by the index-plate is the distance sought.
For use at sea where the instrument must be portable, I arrange it similar to a
binocular or opera glass in one tube of which I place a prism which can be revolved
by a similar drum to that herein before mentioned, and I place, an index-plate or
scale between or over the two glasses or telescopes and by revolving the drum the
image of an object in the telescope or glass in which is placed the prism as
aforesaid is brought to agree with the horizon line in the other glass, or telescope
and the amount of revolution required shews the distance.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent and of
an Order of the Lord Chancellor filed by the said George William Hart in
the Great Seal Patent Office on the 24th July 1882.
GEORGE WILLIAM HART, of 22 Ordnance Row Portsea in the County of Hants.
"AN IMPROVED RANGEFINDER FOR ASCERTAINING DISTANCES AT SEA OR ON
LAND."
The Invention has for its object improvements in instruments for ascertaining
angles, and measuring distances. The means by which my invention is carried
into practice and for the better explanation of which I refer to the accompanying
drawings in which the like letters, designate the like parts are as follows
Figure 1, is a side view of my improved rangefinder. Figure 2 is a plan thereof.
Fig. 3 is a front view, thereof. Figures 4 & 5, are respectively a plan and side
view of the rangefinder, when it is intended for use at sea.
For use on land I construct the instrument thus. I provide a base-plate h
figs 1 & 2 carrying two telescopes B B figs 1 & 2 of which telescopes one is fixed
and is attached firmly to said base-plate. The other Telescope which is moveable
is mounted between upright standards e e fig. 3 which standards, are secured to, a
circular base plate f1 figures 1 & 2. B* fig 3 is the moveable telescope so mounted.
Immediately over the elevated telescope B* fig 3 I provide a tangent screw c
which gears into a toothed pinion-wheel encircling and forming part of said
telescope for the purpose of enabling the same to be turned to the right or left
I provide a pinion D fig 3 which gears, into, a quadrant for the purpose of
elevating or depressing the Telescope. A catch f, figs 1, 2 & 3 furnished with
a pin at one end is caused to drop into a hole i fig 2 in the circular base-plate ƒ'
fig 1 and into a corresponding hole, in another base-plate g figure 1 immediately
under it. When it is desired to rotate the base-plate f¹ figs 1 & 2 upon which
the standards and moveable telescope are mounted said catch fis raised which
frees the upper base plate f¹ figs 1 & 2 from the lower base-plate g figs 1 & 2.
When the upper base-plate is turned 90° the aforesaid pin drops into a corre-
sponding hole in the base-plate g fig 1. I provide a drum D' (shewn in all the
figures) mounted upon a rod 7 figures 3 & 4 which rod has at one end a tangent
screw which gears into the toothed edge of the base-plate g fig 2. Said drum is
engraved with a series of figures which are tangent measurements for a given base.
By rotating said drum both the base-plates f¹ figure 3 and g figure 1 are moved
together and the divisions on the plate 9 shew the degrees whilst the distances
are shown on the drum. I may also use a clamping device k Figure 3 for
effecting the same result. I now proceed to describe the method of using the
instrument on land. The instrument being placed upon a tripod the moveable
telescope is directed towards the object the distance of which is required the
engraved base-plate g fig 1 being placed at 0 or zero when the object is "wired."
The said telescope and upper base-plate are turned 90° to the left or right and a
picket is driven into the ground on the line of sight. The whole apparatus is
then carried and placed over said picket and the uppermost base-plate rotated 180°
so that the picket showing where the instrument first stood can be wired by the
telescope. This having been done the upper base-plate is revolved again 90° to
the left, and the line of sight is then parallel to the line of sight from the first
station but the object being in full front of the telescope when placed at zero at
the first station it is evident that when moved to the other end of the base (which
has been measured) the object will appear to the right (or left) and the drum
attached to the tangent screw is revolved, thereby causing the base-plates ƒ¹ and g

page_text: now clamped together to move through a certain angle the amplitude of which, is
the measure of the distance, and the plate g shows the degrees through which the
telescope has been traversed and the minutes and seconds of arc are shown by the
drum attached to the tangent-screw. The series of figures engraved on the drum
show the distance of the object in yards.
For use at sea I construct the instrument as shown in figs 4 & 5 namely a
bi-nocular glass in one tube of which is fixed a prism m figure 4 which can be
revolved by the drum D¹ which gears by means of the tangent-screw into the
index-plate g¹ and thereby indicates the amount of rotation. Whilst one of the.
Telescopes shows the real horizon the other containing the aforesaid prism m figure 4
shows a horizon more or less elevated or depressed, and as the objects are situated
more or less below the horizon line the index-plate g' will show the amount of
rotation necessary to raise the object to the level of the horizon as seen in the tube
without the prism and hence be a measure of the distance. The scale engraved
on the drum D₁ is constructed and engraved for a definite height above
the sea.
Having now fully described the nature of my said invention and the means by
which the same can be carried into practice I claim what is substantially
mentioned in the foregoing specification and, illustrated in the accompanying
Drawings.
In witness whereof I the said George William Hart have hereunto set my
hand and seal this Twenty second day of July in the year of our Lord
One thousand eight hundred and eighty two,