A Method and Apparatus for Measuring Distances of Objects.
Year: 1889

page_text: Date of Application, 11th May, 1889
Complete Specification Left. 30th Jan.. 1890-Accepted. 1st Mar.. 1890
PROVISIONAL SPECIFICATION.
A Method and Apparatus for Measuring Distances of Objects.
I, CHARLES FRANCIS MARTIN of the 2nd Batallion The Highland Light Infantry,
Depot Hamilton in the County of Lanark, North Britain, Lieutenant, do hereby
declare the nature of this invention to be as follows:-
My invention relates to means of measuring distances of objects as för range
finding, topographical surveying and such like purposes.
.
By means of a suitable mirror or prism I determine a station whence the distant
object appears at or about right angles to a second object. I then pace or measure a
base in the direction of the second object until I come to another station whence
some other distant third object is at or about right angles to the second object.
At this last station I hold a double sight of known width at such a distance from the
eye that I see both the first and the third objects coinciding respectively with
the two slits or points of the double sight. Then by a simple proportion 1 compute
the distance of the first object from the first station, for, as the known width of the
two sights is to the ascertained distance of the sight from the eye, so is the paced or
measured base to the distanco required. The prism or mirror, the double sight and a
tape or other measure for ascertaining the distance of the sight from the eye may all
be accommodated in compact form for the pocket.
BULL
2
1000
ABEL & IMRAY,
Agents for the Applicant.
COMPLETE SPECIFICATION.
A Method and Apparatus for Measuring Distances of Objects.
I, CHARLES FRANCIS MARTIN, of the 2nd Batallion The Highland Light Infantry,
Depot Hamilton, in the County of Lanark, North Britain, Lieutenant, do hereby
declare the nature of this invention and in what manner the same is to be performed
to be particularly described and ascertained in and by the following statement :-
My invention relates to means of measuring distances of objects, as for range
finding, topographical surveying and such like purposes.
I provide an instrument such as is shewn in perspective by Fig. 1. The upper
part of the instrument has fixed in it a prism or mirrors A adjusted to reflect at
right angles, and has attached to it a sight plate B with three equidistant sights
which may be slits xyz. The lower part C forms a casing for a spring tape
one end of which is attached to the upper part. The tape when it is drawn out is held
by an internal catch, which can be released by pressing a knob D, allowing the spring
to wind back the tape. The sight plate B is fitted to slide between two guides on the
face of the casing C, or the upper part of the instrument may be otherwise detachabiy
held to the lower part. In operating with this instrument I proceed as I shall explain
referring to the diagram Fig. 2.
First, at a station R, I sight by the prism or mirrors a distant object P and at the
same time an object or picquet S such that the line RS is at right angles to RP as
determined by the prism or mirrors. I then by pacing, taping, chaining or otherwise,
measure the distance to a point T which is in the same straight line with RS, and
where another distant object Q can be seen by the prism or mirrors to be in a line TQ
at right angles to TR.
Having thus determined the position of the point T and its distance from R, 1
detach the upper part of the instrument having the prism or mirrors and sight
plate from the lower part C, and invert the upper part as shewn in Fig. 3. I

page_text: hold the lower part Cclose against the check and I move away the upper part,
drawing out the tape until I see the two objects P and Q over the two sights x and y.
or y and z.
As the triangle Ty x is similar to PRT, their sides are proportional or
y TTR: RP. The distance between the sights and y being known,
the distance y T being indicated on the tape, and the line R T having been measured,
1 can by the above proportion compute the distance R.P. It is convenient to make
the graduations on the tape equal to the distance between the sights and y, this
distance being thus a unit, so that the above proportion is worked by merely multiply-
ing the measured distance TR by the number of divisions to which the tape is drawn
out. When the objects observed are comparatively near, the two extreme sights a
and may be used, thus doubling the unit, in which case the distance RP is half the
product of the base RT by the tape indication.
There may obviously be additional sights at known units of distance apart, and for
convenience of computation the tape besides having equal divisions may be graduated
also in logarithmic divisions so that by doubling over the tape, it may he used as a slide
rule.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The herein described method of measuring the distance of an object by deter-
mining two base stations at a known distance apart, whence two distant objects
appear in lines at right angles to the base, then from one of the stations sighting
the two distant objects by sights of known width held at a measured distance from
the eye, and computing by proportion the distance of either of the objects.
2. For measuring distances in the manner above referred to, a pocket instrument
provided with prism or mirrors, tape and sights, substantially as described.
Dated this 30th day of January 1890.
ABEL & IMRAY,
Agents for the Applicant.