IMPROVEMENTS IN AZIMUTH COMPASSES
Year: 1879

page_text: LETTERS PATENT to Alexander Louttit, of Osborne Villas, Tollington Park, in
the County of Middlesex, for the Invention of "IMPROVEMENTS IN AZIMUTH
COMPASSES"
PROVISIONAL SPECIFICATION left by the said Alexander Louttit at the Office
of the Commissioners of Patents on the 28th October 1879.
ALEXANDER LOUTTIT, of Osborne Villas, Tollington Park, in the County of.
Middlesex. "IMPROVEMENTS IN AZIMUTH COMPASSES."
My Invention relates to compasses such as are used at sea for the purpose of
observing azimuths of heavenly bodies, my object being to render such instruments
applicable for observing azimuths of stars at night, and to secure accuracy of such.
observations.
I fit to the compass bowl on its underside a small lamp, and by means of a bent
tube, which may be bright inside, or provided with a reflector, I conduct a faint
light from this lamp so as to illuminate a small portion of the compass card imme-
diately in front of the sight to which the eye is applied, which sight is fitted in the
usual way with a prism. In order that this light may render visible a few of the
divisions on the card I make the card of talc or other transparent material in
the usual way. On the opposite side of the compass bowl I provide an upright
gnomon or pin of sufficient size to be visible at night, and behind this I hinge a
inirror, which can be folded on its hinge so that a star can be seen in it, and the
image of the star can be brought into the line of sight. The compass bowl is sus
pended by gimbals mounted on a vertical axis, on which it can be turned until the
image of the star is seen to coincide with the gnomon by an eye applied at the sight,
and at the same time by means of the prism the eye perceives the reading on the
card, which gives the required azimuth. By arranging a graduated circle around
the vertical axis on which the bowl turns the bearing of the star relatively to the
axis of the vessel can be noted at the time of the observation. In order to secure
accuracy of observation I mount the pivot of the card on a slide, which can be
adjusted by setting screws so as to bring the pivot exactly into the line of sight.

page_text: inclined more or less as required, or when not in use it can be folded flat down, as
indicated by the dotted lines. The upper part of the compass is enclosed in the
glass lantern K having sliding doors k, k, opposite to one another to give access
respectively to the eye piece G and the mirror I, and having its side lamps L, L,
for illuminating the compass at night. These lamps are provided with sliding
doors l, l, by which their light is excluded when a nocturnal azimuth observation
is taken. In that case the light from the lamp F passing up the tube E illuminates
a portion of the compass card immediately under the prism, and the card being of
talc or such like material partially translucent the eye can see reflected by the
prism some of the slightly illuminated divisions of the card at the same time that
it observes a star in line with the gnomon H, either directly or as reflected from
the mirror I.
Having thus described the nature of my said Invention, and in what manner
the same is to be performed, I claim as my improvements in azimuth compasses,—
First. The combination of the eye piece and prism, and the gnomon and mirror
opposite thereto, with a lamp arranged under the compass card to illuminate a
portion thereof under the prism, substantially as and for the the purpose herein set
forth.
Second. Mounting the pivot of the compass card so that it can be adjusted to the
line of sight.
Third. The construction of an azimuth compass herein described with reference
to the accompanying Drawings.
In witness whereof, I, the said Alexander Louttit, have hereunto set my hand
and seal, this Sixth day of March, in the year of our Lord One thousand
eight hundred and eighty.
ALEX. LOUTTIT. (L.S.)