Year: 1888

page_text: Ascerta.
I HENRY SAMUEL SPILLER WATKIN, Major Royal Artillery of the Wilderness
Cautwell Road Woolwich, 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 consists of two parts.
1st. An arrangement for ascertaining a right angle, or angle greater or less than a
right angle.
2nd. An arrangement of angle or range drum whereby angles or their corresponding
ranges can be read with great accuracy without a vernier.
The instrument will be better understood by first describing the method of using
it as shown at Figs. 1 and 2.
Suppose C an object the distance of which is required, a position A is selected so
that CAB is as nearly a right angle as the nature of the ground will allow con-
siderable latitude is however permissible.
A second station B distant preferably about 20 of the distance AB, is marked by
a picket B. The instrument is placed over a picket at A, and the image of B as seen
by double-reflection made to co-incide with C as seen by direct vision by manipulating
the milled head screw H (Fig. 5). The act of doing this sets the instrument, so that
on looking through the second eye-hole when at station B, the double reflection of A is
seen in a position D, BD being parallel to A C.
On turning the range drum the reflection of A is moved so as to coincide with C,
and thus measures the angle CBD which is equal to ACB. This is usually registered
on the drum as a range. A subsidary base BE being set out with a flexible cord of
definite length allows of the distance or base A B being measured from station A.
This is accomplished by first setting the sliding collar on the base bar to the number
representing the length of the sub-base adjusting as before the image of B on to (
and then turning the drum so as to cause the image of E. to coincide with C. The
reading on the drum will give the length of the base A B.

page_text: i
The method by which the movement of the adjusting screw (H fig. 5) causes the
mage of picket B to coincide with when working at station A, and the image of A
to appear at D when working at station B is shown in Fig. 3.
CD, DE, are two mirrors exactly at right angles to one another-A B is another
mirror half silvered (the upper half being plain glass) Now if the angle between A B
and CD be 45° that between AB and BE will be 45° and the eye placed at H will
see an object F at right angles to A. H. and the eye placed at K an object G at right
angles to B K.
Now if the mirror AB be moved as shown at Fig. 4 so that the angle between A. B
and CD is say 40° the angle between AB and DE must be 50°, and the double
reflection as seen at H and K would be respectively 80° and 100°, making up the
value of two right angles-and so on for any other movement of the mirror A B.
In this manner the object A (Figs. 1 & 2) is seen reflected at the point D so that BD
is parallel to CA if only the mirror A B (fig. 3) is first sot when at station A so that
the reflection of B is co-incident with C-Generally then the object of this peculiar
arrangement of mirrors is to enable the angle A CB being measured from station B
whether the angle CAB be a right angle or not.
The construction of the instrument for carrying this into practice will now be
understood from the following description.
Fig. 5 shows a plan of the instrument the cover protetcting the mirrors and
containing the eye holes being removed.
QBX an open frame bed plate.
OP steel arm pivoting at O.
On this arm is fixed the frame carrying the mirrors CD, DE. at right angles to
one another-In a frame AB pivoting at F is secured a half silvered mirror and
rigidly connected to the frame is a brass piece FG. A screw GH. regulates the
positio nof FG and therefore of the mirror AB, a spiral spring Y keeping G constantly
pressed against the end of the screw.
A bar B M N pivoted at B has a steel piece at N which is pressed by the action of
a spiral spring Y against the steel face of the drum K.
The angular movement of the bar is thus regulated by the position of the drum K.
working on a screw JK. the movement of this drum is shown by a fixed index L.
and a continuous spiral graduation on the drum.
On the base bar BMN is a sliding collar M with a projecting point which presses
against the straight surface PZ of the steol arm PZO.
It follows from this arrangement that the relativo position of the mirror A B with
the mirrors CD, DE will dopend
1st on the movement of the screw GH. which enables the image of B. fig. 1 to
co-incide with object C as before described.
2nd on the movement of the drum K.
•
3rd on the position of the slider M.
2 & 3 admit of the measurement of the angle DBC fig. 1.
The drum K is engraved with numbers representing ranges, and the base bar BMN
with numbers representing the length of the bases generally employed.
If then the slider M be set to the length of the base A B fig. 1. the number found
opposite the index L when the drum has been revolved so as to obtain co-incidence of
the image of A on to C. will be the range or distanco A C.
A index at the end A of the frame AB (Fig. 5) works over a scale graduated with
figures thus 3210123.
When the index is at 0 it shows that the mirror A B is equally inclined to the
mirrors CD. DE. and that the ranges given on the drum K are the true ranges
but should the index be at 12 or 3 it shows that A B is not equally inclined to
CD, DE. and it will be necessary to deduct 1, 2 or 3 per cent. from the
on the drum to obtain the true distances.
ranges shown
A cover fits over the portion ABXQ having suitable eye holes at Q¹ and X for
viewing the object by direct vision through the upper portion of the mirror A B and

page_text: the double reflection from that mirror and the mirrors CD DE. For long ranges
arrangements are made for inserting a small telescope in these eye holes.
I do not bind myself to the exact construction above detailed as the same 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 the manner in which the same is to be performed I declare that
I claim.
1st. An instrument for measuring angles or ranges with the peculiar arrangement
of mirrors constructed substantially as herein described.
2nd. The arrangement of screw drums and bar for measuring the movement of the
mirror substantially as herein described.
3rd. The arrangement of index and scale for showing the per centage to be deducted
from the ranges substantially as herein described.
1
HENRY SAMUEL SPILLER WATKIN,
Major, R.A.
HENRY SAMUEL SPILLER WATKIN,
Major, R.A.