Improvements in Artificial Horizons.
Year: 1893

page_text: Date of Application, 26th Apr., 1893-Accepted, 27th May, 1893
COMPLETE SPECIFICATION.
Improvements in Artificial Horizons.
I, WALTER PIERREPONT SHADBOLT, of 11 Billiter Square, in the City of
London, Wood Broker, do hereby declare the nature of the said invention, and in
what manner the same is to be performed to be particularly described and ascer-
tained in and by the following statement, that is to say :-
Artificial horizons are instruments used by surveyors and others in conjunction
with sextants and other such like instruments for ascertaining the angular elevation
of a celestial or other body above the horizon when the sea horizon is not visible.
Such an instrument as heretofore constructed generally consists of a dish or trough
containing mercury from the upper surface of which the image of the body is
reflected to the sextant or other angle-measuring instrument employed. This dish
or trough is sometimes covered with a removable glass roof, the object of which is
to prevent currents of air reaching the surface of the mercury and agitating it
while the observations are being made. It also serves, though imperfectly, to
prevent the access of dust and dirt to the mercury while the instrument is in use.
Sometimes the instrument is provided with a reservoir to receive the mercury
when not in use, and this reservoir is sometimes provided with a closable orifice
through which the mercury can be admitted to, or withdrawn from, the said
reservoir.
The objects of my invention are:-
1. To dispense with all loose parts.
2. To prevent disturbance of the surface of the mercury by air or wind when the
instrument is in use.
3. To prevent the mercury from dust and dirt.
4. To avoid the loss of mercury.
5. To avoid the exposure of the mercury to the external air.
6. To allow of the shifting, carrying about or overturning of the instrument
without loss or exposure of the mercury while the instrument is ready for use.
7. To facilitate the removal of scum from the surface of the mercury.
8. To allow of the observation of very small angles of altitude.
To effect these objects I construct the lower part of the instrument in the form
of a reservoir intended to contain the whole of the mercury when the instrument is
not in use, this reservoir is covered with a plate on which the mercury rests when
the instrument is in use the said plate having holes through it communicating with
the reservoir beneath and capable of being opened and closed to a greater or lesser
extent, as may be desired, from the outside of the instrument. The covering plate
is so shaped that its upper surface slopes downwards towards the points where the
aforesaid holes are situated, so that any mercury on the plate will drain off into the
reservoir below through such holes when the same are open and any dirt or scum
will be left behind on the plate. I further fix the glass roof above the aforesaid
plate and reservoir so as to form a closed chamber from which the mercury cannot
escape and into which the external air cannot penetrate.
And in order that my said invention may be fully understood I will now
proceed to describe the same with the aid of the accompanying sheet of drawings
in which
Figure 1 is a side elevation, Figure 2 a sectional elevation taken on line X X of
Figure 3 and Figure 3 a plan of an artificial horizon constructed in accordance with
my invention.
Similar letters of reference relate to like parts in all the figures of the drawings.
A is the reservoir for containing the whole of the mercury when the instrument

page_text: is not in use, or so much of the mercury as is not required to be above the division
plate B when the instrument is in use. The bottom of the reservoir A is closed
with a plate C for example which may be secured to the sides A¹ A³ of the
reservoir A by means of screws D tapped into lugs E cast on the sides of the
reservoir, or otherwise. The plate C must be jointed to the sides A¹ A³ mercury-
tight by suitable packing or otherwise, and in it is provided an opening F for filling
the reservoir A with mercury. This opening is preferably made large enough to
allow of thoroughly cleaning out the reservoir through it and is closed with a screw
stopper G. This stopper is preferably made so that it can be screwed in or out by
hand without the aid of any tool; but care should be taken that when the said plug
is closed no part of it shall project down so far as to prevent the instrument from
standing steadily upon three legs when in use. In Figures 1 and 2 two only of these
legs are seen marked H.
The plate B is provided with holes or passages I leading to the reservoir A.
These holes can be opened or closed at pleasure by means of the screw valves or
stoppers J which can be operated from outside the instrument. The upper surface
of the plate B is made to slope downwards towards the holes or passages
I as shown
in Figure 2. The sides K of the chamber above the plate B are formed as upward
prolongations of the sides A¹ of the reservoir A. The apices of these sides are
connected together by a cross bar L, and the frames M containing the glass
plates N forming the roof are secured mercury-tight by screws P, or otherwise, to
the said crossbar L, to the sloping edges of the sides K, and to the upper edges of
the ends A¹ of the reservoir A. The glass plates N are cemented mercury-tight
in the frames M and these with the glasses N are inclined to the centre of the
instrument at an angle of 45°, or thereabouts, to the vertical.
Instead of mounting plates of glass N in frames M and securing the latter to the
parts A², K and L, plates of glass truly ground and polished and without frames
may be secured in the same position by means of the screws P passing through holes
formed in the said plates of glass.
The four sides of the reservoir A, the plate B, the sides K of the upper chamber
and the cross-bar L may all be cast in one piece in one piece of metal; it is obvious
however that the parts to be cast together may be varied according to circumstances,
and in some cases instead of casting several parts together the instrument may be
made up of several pieces joined together in any suitable way; but in that case care
must be taken that the parts are very firmly secured together, and that all the
joints are perfectly mercury-tight. The frames M, or the plates of glass used
without frames may conveniently be secured to the parts A³, K and L by means of
screws as shown, but any other mode of securing them may be employed that will
admit of their easy removal to enable the interior of the upper chamber to be
cleaned.
The instrument may be made of any suitable material but all parts that come
in contact with the mercury must be made of, or lined with such material as has
no effect on mercury, and is not acted on thereby.
By fixing the glass roof mercury-tight to the edges of the sides K and A³ the
upper surface R of the mercury on the plate B may be raised above the upper
edges of the lower bars of the frames M (when frames are used) or above the
upper edges of the plate B when plates of glass without frames are used, whereby
the surface of the mercury impinges upon the inner surface of the transparent
roof and the whole surface or nearly the whole surface of the mercury is brought
within view of the observer so that the reflection of a body from the surface of
the mercury at a very low angle is not interfered with.
It will now be understood that when a sufficient quantity of mercury has been
charged into the reservoir A through the opening F, the stopper G screwed into
place, and the valves or stoppers J closed against the ends of the holes or
passages I the instrument may be moved about from place to place without fear
of the mercury escaping, as it is confined in the mercury-tight reservoir A. When
it is desired to use the instrument it is only necessary to open the holes I by

page_text: unscrewing the valves or stoppers J a short distance and tilting the instrument
up so as to allow a sufficient quantity of mercury to flow out of the reservoir A
through the lowermost of the holes I into the compartment above the plate B, air
entering, through the other hole, from the said compartment into the reservoir A in
proportion as the mercury quits the latter, then on closing the valves J and
turning the instrument into the horizontal position the mercury spreads over the
plate B and its upper surface is available for making the required observations,
being shielded from currents of air or wind, and protected from dust and the
external air by the fixed roof M N. Moreover in the event of the instrument
being overturned while the mercury is in the upper compartment, the said mercury
cannot escape by reason of the joints of the various parts being made mercury-
tight. When it is desired to return the mercury to the reservoir A the valves or
stoppers J are opened and the mercury drains off the plate B, the lower part of
the mercury passing first through the holes I and the upper part last, thus tending
to leave on the plate any solid matter or scum that may have been floating on the
mercury and this solid matter or scum can be afterwards removed from the plate
by taking off one of the glass frames M N. It will be understood that any dirt
or scum in the reservoir A floats on the top of the mercury therein when the
instrument is tilted up, and is consequently retained in the said reservoir along
with the excess of mercury that is not required for use in the upper compartment.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I desire to have it
understood that I make no claim generally to the use of mercury for an artificial
horizon or of a glass roof over the trough containing the mercury, or of a reservoir
to contain the mercury, or of a closable hole or passage to let the mercury into
or out of the reservoir, as I am aware that these are not novel per se, but that
what I do claim is :-
:-
First. Constructing an artificial horizon with a glass roof fixed mercury-tight to
the instrument substantially as hereinbefore described, and illustrated in the
drawings.
Second. Constructing an artificial horizon with two mercury-tight compart-
ments divided from one another by a plate adapted to form the top of the lower,
or reservoir compartment, and the bottom or floor of the upper or observation
compartment, the said division plate being provided with closable holes or
passages for the transference of the mercury from one compartment to the other,
substantially as hereinbefore described, and illustrated in the drawings.
Third. In an artificial horizon constructing the plate or floor on which the
mercury rests, with its upper surface sloping towards the holes or passages
through which the mercury is drained off from such plate or floor substantially
as hereinbefore described, and illustrated in Figure 2 of the drawings.
Fourth. The construction of an artificial horizon in such manner that the surface
of the mercury can be raised to such a height in the instrument that the whole
or nearly the whole of such surface is brought within view of the observer, substan-
tially as hereinbefore described, and illustrated in Figure 2 of the drawings.
Dated this 20
20th day of AJH 1898.
1000
W. P. SHADBOLT,
Per W. H. Beck,
115, Cannon Street, London, E.C., Agent.