Improvements in Instruments and Appliances for Ascertaining Distances.
Year: 1889

page_text: Date of Application, 19th Nov., 1889-Accepted, 28th Dec., 1889
COMPLETE SPECIFICATION.
Improvements in Instruments and Appliances for Ascertaining
Distances.
I, HENRY SAMUEL Spiller Watkin, of the Wilderness, Woolwich, in the county
of Kent Major Royal Artillery 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 :-
The instrument and appliance consist of three parts
(a). An optical square, fitted with a telescope, and hinged flap.
(b). A telemeter by which the distance are read off on a drum.
(c). A peculiarly constructed cord which forms a base, at the ends of which the
instruments are worked.
The optical square is shown in Fig. 1. and Fig. 2. A B C D is a rectangular box
(having the sides fluted to give additional strength when required), and made prefor-
ably of an alloy of aluminum containing about 20 per cent. of aluminum. EF is
the index glass wholly silvered, G the horizon glass half silvered, and placed at 45
to E F. His a telescope which can be used instead of a plain eye hole when
required to obtain greater definition. M is a hinged flap, on which is screwed a
piece of ivory L. The opening K for observing the object is contracted as much as
possible, so as to prevent rain driving in on the mirror. Fig. 3 shows a plan of the
telemeter with the cover removed. A B C D is a rectangular box (the sides of
which may be fluted to give additional strength) and preferably made of the same
alloy as described for the optical square. T is an aluminum arm cast with suitable
fittings for fixing on an index glass. A german silver spring O is firmly secured
to this arm, and also to the box at C. The spring is so arranged that the end of
the arm T constantly presses against the point of the screw M². An horizon
glass G¹ half silvered is secured firmly to the base of the box, at an angle of 45° to
the normal position of the index glass E F¹. A block S is secured to the base of
the box, in which works the screw M2, this screw is revolved by the drum N in a
manner hereafter described. On the drum are engraved figures representing yards,
or other units of measurements. A telescope H' can be employed in lieu of a sight
hole when required.
A flap M is fitted to the telemeter similar to that described for the optical square.
In the normal position of the instrument the arrow on the drum N is opposite the
index point, when in this position the mirrors F1 F1 and G₁ are exactly at an angle
of 45°, so that objects viewed by direct vision through the plain part of the horizon
glass are at exactly at right angles to those in coincidence with them as seen by
double reflection. As the drum N, and consequently the screw M², is revolved, the
angle of inclination of the mirrors is reduced owing to the spring O pressing the
arm I against the screw M². The amount of this inclination is measured by
the figures engraved on the drum, which are calculated in distances for the base
employed.
The peculiar nature of the screw which constitutes one of the main features of
this invention is shown in Fig. 4, which is an enlarged section through the centre
longitudinally. Al² is a fine screw say of 30 threads to the inch, P being an
enlarged cylindrical continuation of the screw part M², in which is cut a longitudinal
key way, in which a feather Q slides. R is a hollow cylinder forming part
of the pedestal S, in this is cut a female screw with say a pitch of 10 threads to
the inch.
A hollow cylinder V is cut with a screw, to fit the screw cut in R. The feather Q
is secured to the cylinder V. The cylinder V is soldered to a circular base ✗, to
which is also secured the drum N.

page_text: It follows from this arrangement that on turning X, the drum N is revolved, which
in its turn, by means of the feather Q rotates the screw M². The screw M² is
withdrawn at the rate of 3 of an inch for every turn, but V and N at the rate
of of an inch at every turn. In this manner a slow rate of advance of the
screw M² is ensured, which serves to record minute variations in the inclination
of the index glass É F₁ Fig. 3. while the more rapid movement of the drum N
allows of a readable spiral scale being engraved on its surface.
The cord used as a base for working the instruments, is the outcome of several
experiments to obtain a flexible cord, which would alter little with variations of
tension and atmospheric changes. It is composed of several strands (generally 4) of
a hemp cord made with little or no twist, these strands are joined together by an
outer covering of silk woven on. The whole is then boiled in melted paraffin wax.
The cords are of 12 yards lengths, the ends being fitted with spring hooks for
looping them together. The cords are generally wound on a fishing reel which is
attached to a belt fastened round the waist. The method of obtaining distances is as
follows. Two cords are looped together, thus making a length of 25 yards, one end
is then fastened to the optical square, and the other to the telemeter. The observer
with the optical square moves into such a position as to obtain coincidence with the
object viewed by direct vision, and the ivory mark on the telemeter by double
reflection, thus placing himself in the right angle between the object observed, and
the observer with the telemeter. The observer with the telemeter revolves the drum,
until he also brings the object and the ivory on the optical square into coincidence.
The reading on the drum opposite, the index will then give the distance of the
object observed. Should the space be restricted, only one cord is used, but the
ranges read on the drum must be halved. If greater accuracy is required four
cords may be hooked together, making a base of 50 yards, in which case the
reading on the drum must be doubled.
A suitable scale on the lid of the instrument allows of any readings being
halved or doubled at sight.
To obtain ranges of moving objects all that is required is for the observer with
the optical square to constantly obtain coincidence by swaying his body, and shifting
his position. In this manner the ranges of Artillery, Cavalry, and Infantry in
motion have been taken; five or six ranges per minute being obtained, to an
accuracy of one per cent.
I would remark that the above described methods of carrying my invention into
effect are those I have found to answer, but I do not confine myself to the precise
details shown and described, as such may be varied without departing from the
peculiar character of my invention.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is
(1) The peculiar arrangement of screw and drum, substantially as herein
described.
(2) The arrangement whereby the said screw is applied to form a telemeter,
substantially as herein described.
(3) The construction of cord for use with the telemeter, substantially as herein
described.
Dated this 19th day of November 1889.
HENRY SAMUEL SPILLER WATKIN,
Major R.A.