IMPROVEMENTS IN INSTRUMENTS FOR MEASURING ANGLES AND TAKING ALTITUDES
Year: 1858

page_text: LETTERS PATENT to Henry Glover, of New York, United States of
America, Mathematical Instrument Maker, for the Invention of
"IMPROVEMENTS IN INSTRUMENTS FOR MEASURING ANGLES AND TAKING
ALTITUDES."
Sealed the 25th January 1859, and dated the 26th July 1858.
PROVISIONAL SPECIFICATION left by the said Henry Glover at the
Office of the Commissioners of Patents, with his Petition, on the
26th July 1858.
I, HENRY GLOVER, of New York, United States of America, Mathematical
Instrument Maker, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN INSTRUMENTS FOR MEASURING ANGLES AND TAKING ALTITUDES,"
to be as follows:-
My Invention is designed for the purpose of measuring the angular distance
of two or more objects from each other, and consists of improvements upon
that class of reflecting instruments which are of the sextant and quadrant..
kind. By means of my said improvements I am enabled to measure at one
and the same time, if occasion require it, not only the angular distance of two-

page_text: celestial or other similarly situated objects, but their altitude above the
horizon also I can also obtain the zenith distance of an object without a
;
sea or artificial horizon. An instrument constructed with my improvements
when arranged for measuring the angular distance of two objects, together
with their altitude, consists of two graduated arches combine: in such manner
that the plane of one arch shall be at a right angle to that of the other.
Each arch has a limb attached with nonius as usual in sextants, and as also
reflectors placed on the end through which the axis pin is placed; one of
these arches measures the altitude, and the other the angular distance between
two contiguous objects that are at the same altitude. The arch measuring the
distance apart lies horizontally, and that which measures altitude is verical when
held in position for conducting observations. The two will be called therefore
the horizontal and the vertical arches in the description, although, in taking
some observations, these positions will not be rigorously observed.
The vertical arch is seen at A in the Figures I. and II. of the Drawings
annexed, and as there representated is substantially a sextant frame having its
limb B with nonius C and inirror D, as usual.
The horizontal arch is seen at E, attached to the front leg of the frame of
A, at that part where the horizon glass is usually placed in the ordinary
sextant; it has a limb F, with nonius scale, as in the other arch and as
represented. At the axis of this limb is an inclined mirror or reflector G,
which, by being attached to the said arm, follows it in its movement along the
arch E; at this part of the instrument there is also another mirror or reflector
G', but this one is so attached to the frame of A as to be capable of movement
on an axis pin passing from the end of the said mirror into the said frame.
In connection with this mirror is a post H, at the top of which is the sighting
piece or telescope H', through which the reflected object is viewed. The
mirrors G and G¹ are placed so as to stand at an angle to each other, which
angle.may be varied by moving the arm H. The mirror G, however, always.
being placed so as to be parallel with D, when the limb to which the latter is
attached is upon zero of the graduated arch. This angle causes them to have
the general position of the letter V, when the upper and lower edges of their
frames are parallel. As, however, the mirror G moves with its limb F, this
parallelism is only maintained when the said limb is at the centre of its arch
E; the other angle is constant however the limb F may be moved. It is
this feature, viz., that by which the angle of glasses laterally may be changed
without alteration of the angle at which the ends incline, that the angular dis-
tance of two objects, together with their altitudes, may be simultaneously
iueasured.

page_text: On the back of arch A there is a second arch I of smaller dimensions
secured to the first at a short distance from it, but so that the two will be
parallel. The front leg of the frame is also to be in line with that of A, as
seen in the back view, Figure II. The limb I to this arch carries a cross
level at its head, as at J, which is fixed upon a centre, & has its ends
supported by adjusting screws, as shewn. The limb I' is to be at the zero
upon the other arch, and the bubble of the level must then be in the middle.
It will be seen from the position of the sighting points HI' that one eye can
be viewing the position of the level while observing the objects to be measured
with the other eye. The method of using is as follows:-It is desired to
observe the altitude, and at the same time the angular distance apart of two
objects, as a, y; the limb B must be brought to the zero on its arch, then, by
holding the frame A in a vertical position, and so as to present the instrument
toward the object, get a near adjustment by looking down with the naked eye
placed near the sight H' upon the mirror G, until a is seen within it; then
view it through the sight or telescope H¹, if need be, moving the arm H to
alter the angle of the glass G' to that of G, the limb F being at zero (which
is at the middle of its quadrant). The course of the ray from a will be first
to the mirror D, and thence it will be reflected upon G, and from that upon
G; the angle of incidence must there be such as to reflect it vertically to the
eye. The limb B having been clamped at zero, it will be found that to get this
course for the ray from the object a, the arm or post H has been slightly
moved, so that both arms and limbs are held at the time of the observation
in a perfectly perpendicular position. This will have thrown up the front leg
of the frame equal to half the altitude of the object. The observer now
keeping the star (if that be the object measured) on the cross bars of his
telescope with one eye, and then looking down upon the level with the other,
moves the limb I¹ along, until the bubble is seen in the middle; the arch
may now be read off, which will give the altitude.
Now, to measure the distance of y from a, when they are at nearly the
same altitude, keeping x in the field, as before, move the limb F until y
appears in the field; continuing the motion, it will approach a; and when the
two coincide the arch F may be read off, and will be the angular distance.
In case the two stars are at the same exact altitude, they will eclipse each
other in the telescope, and of course the angular distance in such case will be
more exactly ascertained than when the two differ in altitude. To get the
difference of altitude, procced as before described for x, by bringing y to the
cross lines, and adjusting the level anew.
A part of these improvements are also applicable to quadrants, whereby

page_text: they are capable of measuring an object in altitude, either by sea horizon, as
usual, or by zenith distance, in case the horizon is at any time obscured while
the sky is clear above. For this purpose all may be dispensed with except the
two mirrors G and G¹, and the vertical sight. These mirrors are only partly
silvered, and hence an eye piece or sight placed, as usual, upon the arm of
the frame horizontally opposite, enables an observation to be taken from the
horizon, as in that by a zenith distance. For this latter mode a vertical sight,
as H, will have to be used in the manner already described for measuring
two objects.