A NEW OR IMPROVED RANGE FINDER OR DISTANCE MEASURER
Year: 1878

page_text: PROVISIONAL SPECIFICATION left by George William Hart at the Office
of the Commissioners of Patents on the 25th July 1878.
GEORGE WILLIAM HART, of Croydon, in the County of Surrey, Engineer. "A
NEW OR IMPROVED RANGE FINDER OR DISTANCE MEASURER."
This Invention relates to a new or improved range finder or distance measurer.
According to my Invention the distance of an object is ascertained by reading off
upon a scale on the base of a right angled triangle divisions equivalent to the angle
of two lines of sight denoted by an index scale, the two sides of the triangle, i.e., the
perpendicular and the hypothenuse, being the two lines of sight to the object, and
the length of the base varying with the distance of the object observed, which is
seen at the apex of the triangle, the distance thereof being measured by the width
of base required to enable the perpendicular line of sight to meet the object on the
oblique line.
The oblique line of sight in my instrument is obtained along what I term a
radius arm, the angle of which to the base may be set at pleasure. The part of the
instrument forming the other line of sight at right angles to the base has a sliding
action along the base (so that the latter may be lengthened or reduced), but is
always at right angles thereto.
For the base I divide a space of 6.282 inches or some decimal part or some
multiple thereof, the reason for this being to enable me to obtain decimal readings
of the length of the base instead of other parts, 6-282 being the proportion of circle
circumference to radius; also for setting the radius arm for the oblique line of sight
I provide a scale to enable it to be set to the decimal of a degree.
To illustrate my Invention, as the cord of arc of an angle is to the radius as 1 in
57.35, then if the radius arm of the instrument be in length 57-35 inches, it follows
that for an angle of one degree it will be at its end one inch out of perpendicular
to the base. The oblique line of sight being along the radius arm, will therefore
meet at 57-35 the perpendicular line of sight with one inch base, and the object
(apex of triangle) will be distant 57-35 inches from the observer, i.e., 57.35 times
the length of the base line. The base line being divided to scale, the distance of
the object may thus be read off;

page_text: If the angle of oblique line of sight be decreased to the decimal of a degree or the
radius arm be shortened, the value of the divisions of the base line becomes pro-
portionately increased. I may have a telescope on each line of sight, but I prefer
employing only one, and that by preference on the oblique line of sight. Or a hair
sight may be substituted for the telescope.
The other line of sight when not furnished with a telescope has a prism or
reflector, so as to reflect the image of any object, along a line parallel to the base on
to another prism or reflector in the field of view of the telescope. One half of the
field of view of the telescope affords a direct sight of the object, whilst the lower
half of the field is stopped by the reflector, and the ray passes to the other reflector 1
and thence to the object.