An Improvement in or relating to Sextants and like Instruments.
Year: 1897

page_text: PROVISIONAL SPECIFICATION.
An Improvement in or relating to Sextants and like Instruments.
I, EDWARD PLUMSTEAD, of Henry House, Putney Vale, in the County of Surrey,
Private Secretary, do hereby declare the nature of this invention to be as
follows:-
This invention relates to an apparatus adapted to be applied to any instrument
used for taking altitudes of celestial bodies, or for solving problems in navigation,
surveying and the like, and it consists essentially of a pendulum adapted to be
attached to the instrument to be used. This pendulum carries a point adapted
when it comes into contact with a similar point on or attached to an arc on the
instrument to complete an electric circuit which gives an audible signal, thus
indicating that the instrument is being held either vertically or at any desired
angle. The electrical contact is preferably so arranged that if the observer
wishes to take an observation after dark the current also lights a small electric
lamp the light of which is so shaded and directed that although it is sufficient to
illuminate the wire of the instrument it is not sufficient to eclipse the planet or
star being observed.
I do not limit myself to the use of any particular form of pendulum or to any
specific means of obtaining either the electric current or completing the electric
circuit as these may be effected by any of the well-known methods.
By the use of this apparatus the observer can concentrate his whole sense of
sight on the observation, as his sense of sound will indicate to him when the
instrument is being held in the proper position for taking the observation.
D
1
. 100
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An Improvement in or relating to Sextants and like Instruments.
I, EDWARD PLUMSTEAD, of Henry House, Putney Vale, in the County of Surrey,
Private Secretary, 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 relates to an apparatus adapted to be applied to sextants and
like instruments used for taking altitudes of celestial or terrestial bodies, or for

page_text: solving problems in navigation, surveying and the like, and it consists essentially
of a pendulum mounted on the instrument and adapted when the instrument is
held vertically i.e., perpendicularly, or at any predetermined angle, to complete
an electric circuit which gives an audible or visible signal or both in combination.
In the accompanying drawing which illustrates by way of example one applica-
tion of this invention:-
Figure 1 is a view in elevation of an edge bar sextant fitted with the apparatus
for giving either or both an audible and visible signal.
Figure 2 is a view in section on line 2-2 of Figure 1 and
Figures 3 and 4 are detail views.
Throughout the views similar parts are marked with like letters of reference.
A pendulum A is carried and adapted to swing on a centre B which is prefer-
ably formed with a knife edge as shown. This centre B is mounted on the back
of the frame X of the instrument and is extended to form one of the legs on
which the instrument rests when lying face upwards. The underside of the bulb a
of the pendulum A carries a contact piece C, which although shown rigidly
mounted may conveniently take the form of a spring to make it more sensitive.
This contact piece C comes into contact with an adjustable contact screw D carried
by a block fixed to the frame X of the instrument, and so completes an electrical
circuit.
By means of the adjustable contact screw D the position of the contacts C and D
with respect to one another are so adjusted that the electrical circuit is only
completed when the instrument is, held in a truly vertical or perpendicular
position, that is to say when the telescope W is truly horizontal or at right angles
to the pendulum A and the shape of the said 'contacts is such that they do not
engage unless the pendulum is swinging in a plane parallel to the instrument.
The contacts C and D. are arranged either in an ordinary electric-bell circuit
whereby an audible signal is given or in an electric-lamp circuit whereby a visible
signal is given, or in a joint circuit so that both signals are given simultaneously.
The electric bell and battery therefor may be of any suitable type and arranged
in any convenient manner.
The electric glow lamp E is carried in any convenient form of holder such as e
capable of being removably held within a spring socket F. This socket F is held
through the medium of hinged and adjustable arms f behind the screens y of the
horizon glass Y.
The visible signal is most useful for night work as it not only serves to indicate
that the instrument is being held vertically or perpendicularly but also to
illuminate the wires of the telescope.
Instead of using the lamp for a visible signal it may be used as an illuminant
only in which case it is placed in an independent electrical circuit.
The lamp E is made readily removable from the socket F to allow it being used
for reading either the arc or the watch.
The pendulum A is preferably cut away at its middle as shown to allow of it
being readily removed from the instrument by passing over the handle Z after
first removing the nut b.
In practice the instrument is held as steadily as possible and the index bar V
moved until the image of the body under observation is coincident with the central
point of the telescope W. A very little practice enables the operator to depress
the telescope W until contact takes place, at the same time manipulating the
tangent screw U so that at the instant of contact the image is brought to the
junction of the wires in the telescope. The altitude is then read off in the usual
way.
Used with the hand alone altitudes can be taken with considerable accuracy
at any time that the object under observation is visible. Resting the hand or
instrument upon a staff, or slinging it so as to relieve the hand of its weight,
materially increases its usefulness,

page_text: It will be understood that the contacts C and D are connected to the leads of
an electric bell or other circuit in any convenient manner, that shown on the
drawing being by way of illustration only.
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 apparatus hereinbefore described for application to sextants and like
instruments for giving an audible or visible signal or both in combination when
the said instrument is held vertically or at any other predetermined angle.
(2) In a sextant or like instrument the use of a pendulum so mounted and
arranged as to complete an electrical circuit when the instrument is held vertically
or at any predetermined angle.
(3) In a sextant or like instrument, the employment of an audible and, or,
visible signal for the purpose of indicating when the instrument is being properly
held for taking the desired observation, as set forth.
12th day of May 1898.
ROBERT E. PHILLIPS, Assoc. M. Inst. C.E., M.I. Mech. E..
Consulting Engineer and Patent Agent,
70, Chancery Lane, London, W.C., Agent for the Applicant.