Year: 1886

page_text: Date of Application, 30th July, 1886.
Complete Left, 25th Feb., 1887.
Complete Accepted, 29th July, 1887,
I, GEORGE PALMER EVELYN of the Army & Navy Club, Pall Mall in the County
of Middlesex, Honorary Colonel 3rd Battalion East Surrey Regiment do hereby
declare the nature of this invention to be as follows:-
This invention has for its object an instrument for measuring angles of altitude.
My improved instrument resembles an ordinary sextant insomuch that the object to
be observed is seen by double reflection whilst the observing telescope is pointed
approximately in a horizontal direction. As in a sextant one of the reflecting mirrors
is movable, it is set to a suitable inclination to bring the image of the object to the
position required and the angle of elevation is then read off on a graduated scale.
My improved instrument however is intended for use when a natural horizon is not
available; it is provided with a spirit level or glass tube charged with liquid and con-
taining a small air bubble. Over this tube there is a reflector preferably a prism and
the reflection is at an internal surface. The telescope tube is fitted up with half lenses,
and in looking through the tube the reflecting prism is seen directly without the inter-
vention of lenses. When the telescope is held horizontally the image of the bubble
comes into view through the telescope tube being reflected in the prism. When the
instrument is suitably set and directed the object to be observed is also simultaneously
seen through the half lenses of the telescope and after reflection in the two ordinary
sextant mirrors. This image of the object being brought to coincide with that of the
bubble the double angle of the mirrors is read off on the graduated limb and this is
the altitude required.
I employ preferably a very small bubble and this I obtain by closing the end of the
glass tube with a cork or stopper having in its end a cavity of dimensions such as to
contain a bubble of the size desired. The tube is completely filled with liquid and the
cork is then thrust in displacing a portion of the liquid which escapes around its sides.
Then when the tube is inverted the bubble passes out of the cavity to its place in the
tube. By these means the size of the bubble can be accurately adjusted and it can be
renewed at any time with great facility.
This method of obtaining a suitable bubble is described in the specification of a
former patent granted to me No. 1964 in the year 1885.
'
11
2011 1
T-1 1000
CARPMAEL & Co.,
Agents for the Applicant,

page_text: I, GEORGE PALMER EVELYN of the Army and Navy Club, Pall Mall in the County
of Middlesex, Honorary Colonel 3rd Battalion East Surrey Regiment, 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 :-
This invention has for its object an instrument for measuring angles of altitude.
My improved instrument resembles an ordinary sextant insomuch that the object to
be observed is seen by double reflection whilst the observing telescope or tube is
pointed approximately in a horizontal direction. As in a sextant one of the reflecting
mirrors is movable-it is set to a suitable inclination to bring the image of the object
to the position required and the angle of elevation is then read off on a graduated
scale.
My improved instrument however is intended for use when a natural horizon is not
available; it is provided with a spirit level or glass tube charged with liquid and con-
taining a small air bubble. Over this tube there is a reflector preferably a prism and the
reflection is at an internal surface. The telescope tube is fitted up with half lenses, and
in looking through this or the observing tube the reflecting prism is seen directly
without the intervention of lenses. When the telescope or observing tube is held
horizontally the image of the bubble comes into view through the telescope or tube
being reflected in the prism. When the instrument is suitably set and directed the
object to he observed is also simultaneously seen through the half lenses of the telescope
or through the observing tube and after reflection in the two ordinary sextant
mirrors. This image of the object being brought in contact with that of the bubble
the double angle of the mirrors is read off on the graduated limb and this is the
altitude required.
I employ preferably a very small bubble and this I obtain by closing the end of the
glass tube with a cork or stopper having in its end a cavity of dimensions such as to
contain a bubble of the size desired. The tube is completely filled with liquid and the
cork is then thrust in displacing a portion of the liquid which escapes around its sides.
Then when the tube is inverted the bubble passes out of the cavity to its place in the
tube. By these means the size of the bubble can be accurately adjusted and it can be
renewed at any time with great facility.
This method of obtaining a suitable bubble is described in the specification of a
former patent granted to me No. 1964 in the year 1885.
In order to control and render manageable the action of the bubble the curvature of
the glass tube is much greater than that of an ordinary spirit level. I prefer one of a
radius of 12 inches giving about 5° in an inch of circumference and being about equal
to the distance of distinct vision or of the horizon glass of a sextant from the eye.
This makes the movement of the reflected bubble in the prism approximate to the
vertical angular movement of the sea horizon in the glass of a sextant. The bubble

page_text: horizon is therefore as manageable and sensitive as the sea horizon and may be much
more or less so by using levels of greater or less curvature.
In order that my said invention may be fully understood and readily carried into
effect I will proceed to describe the drawings hereunto annexed.
DESCRIPTION OF THE DRAWINGS.
Figure 1 is a side view of the complete instrument and Figures 2, 3, 4 and 5 shew
details of the level and its attachments.
In figure 1 a is the telescope or observing tube, b is a mirror fixed to the arm c
which is pivotted at its upper end and at its lower end carries the vernier d by which
the graduations on the arc e are read. f is another mirror fixed to the frame. The
arm c is shewn at about the zero point so that rays from the object under observation
would come to the mirror 6 in an almost horizontal direction. From thence they
would be reflected on to the mirror f by which they would be again reflected to the
telescope or observing tube a. The whole of the above arrangement is that adopted in
an ordinary sextant.
9 (figures 3 and 5) is a spirit level consisting of a curved bottle closed by the
cork g which has a recess in it as above described. The level 9 and its cap; is
enclosed in the metal tube / which is slotted at the bottom to receive the pin j¹ on the
cap which is thereby prevented from turning when the second cap k is screwed on
to the tube h. The tube his carried by another tube at right angles to it which is
fixed to the bracket attached to the frame of the instrument. The tube is open at
its lower end (as shown in figure 3) and a ray of light is thrown into it by the
reflector m. This ray passing through the spirit level is internally reflected into the
telescope or observing tube a by the prism n fixed to the top of the tube / the mirror f
(figure 1) not standing out sufficiently from the frame to intercept it. A cross wire o
is provided to mark the centre of the tube l.
The
In using the instrument it must be so held that on looking through the telescope or
observing tube a the bubble of the spirit level is seen bisected by the wire o.
image of the object whose altitude is to be observed is (by moving the arm c) brought
to the centre of the field and its altitude is then shewn by the graduations on the
arc e.
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. An instrument for measuring angles of altitude in which the object and the
bubble of a spirit level are viewed simultaneously substantially as described.
2. Regulating the curvature of the level so that the movement of the image of
the bubble as seen through the instrument shall approximate to that of the horizon as
viewed through an ordinary sextant.
3. An instrument for measuring angles of altitude arranged substantially as
described and shewn in the drawings.
Datad this 95th day of February 1887