Improvements in Horizon Glasses for Sextants and the like.
Year: 1894

page_text: Date of Application, 8th Sept., 1894--Accepted, 13th Oct., 1894
COMPLETE SPECIFICATION.
Improvements in Horizon Glasses for Sextants and the like.
I, GEORGE CHARLES LILLEY of 10 London Street, Fenchurch Street, in the-
City of London Compass Maker, do hereby declare the nature of my invention
and in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement :-
My invention has for its object to make horizon glasses for sextants, and the
like, in such a manner, that the silvering of the mirror portion is effectually
protected from injury from the penetration of moisture or from other cause.
According to my invention I cover the whole of the back of the glass, including
both the transparent and the silvered portion, by a sheet of sufficiently transparent
material, such as glass, which is preferably cemented to the back of the sextant
horizon glass or the like.
The accompaning drawing represents a sextant horizon glass or the like provided
with a transparent backing according to my invention.
Figure 1 is a front view a representing the transparent portion and 6 representing
the silvered portion. Figure 2 is an edge view and Figure 3 is a transverse section-
c is the backing of trans--
the silvering being indicated by the thickened line b²
parent material such as glass. It extends over the whole of the transparent and
silvered portions of the sextant horizon glass or the like and is preferably cemented
thereto by Canada balsam or like cement which will not interfere with the proper-
transparency of the part a.
The glasses and the transparent backing are mounted in a frame or carrier which
may be done in the usual way and in order to utilize existing frames, or carriers,
I may make the glass, and its transparent backing, of such a thickness that.
together they are about the thickness of ordinary sextant horizon glasses or
the like.
In order that the transparent backing may be truly parallel with the sextant
horizon glass or the like I may provide at the corners as at d or at the side edge
or top edges or at all three edges or any desired portions thereof films or the like.
of a thickness equal to that of the silvering at so that the backing may be
maintained at the same distance from the transparent portion a as it is from the
silvered portion b. This can be most conveniently effected by leaving portions of
the silvering at the corners or edges or any portions thereof.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. A horizon glass for sextants or the like provided with a transparent backing.
extending over the whole of the transparent and silvered portions of the said glass.
substantially as herein before described.
2. A horizon glass for sextants or the like provided with a transparent backing
extending over the whole of the transparent and silvered portions of the said glass
and with silvered portions or distance films at or towards the corners or edge or
edges of the transparent portion of the said glass for securing parallelism of the
backing with the said glass substantially as herein before described.
Dated the 8th day of September 1894.
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, W.C., Agents.