AN IN- PROVED REFLECTIVE LEVELLEB."
Year: 1856

page_text: LETTERS PATENT to William Barrie, of Maida Hill, London, in the
County of Middlesex, Commander R.N., for the Invention of "AN IN-
PROVED REFLECTIVE LEVELLEB."-A communication from Adolphe Morlot,
of Montreux.
Sealed the 4th July 1856, and dated the 9th January 1856.
PROVISIONAL SPECIFICATION left by the said William Barrie at the
Office of the Commissioners of Patents, with his Petition on the 9th
January 1856.
I, WILLIAM BARRIE, of Maida Hill, London, in the County of Middlesex,
Cominander R.N., do hereby declare the nature of the said Invention for
AN IMPROVED REFLECTIVE LEVELLER" to be as follows:-
'The applicationoroneormoremirrorsto telescopes, and all other instruments
where a level is required, in such manner as to enable the observer to obtain
a true level while looking through the instrument, without direct reference to
the air bubble in the liquid contained in the glass tube of the level, and
consequently without any tripod or other apparatus for fixing the instrument.
The annexed Diagrams will assist in explaining the means by which this
important object is attained. Fig.1 represents a vertical longitudinal section,
and Eig.2 a vertical transverse section, of a telescope fitted with my improve-
ments. A mirror A,of glass or metal (the latter being preferable), is fixed with
its uppersurface at an angle of 45° to the axis of the instrument, immediately

page_text: beneath the centre of the liquid level B. The air bubble in the glass tube
is reflected in the mirror, and when the centre of the reflected bubble is
brought by the observer to correspond with a lino marked across the mirror
at the axis of the tube of the telescope C, the instrument is levelled. The
glass tube B is adjusted parallel with the axis of the telescope, by means of
the springs, and screw a, shewn at Fig. 3. By reference to Fig. 2, the
relative positions of the liquid level and the mirror will be seen. The glass
tube B is placed a little on one side of the centre of the instrument; the
inner edge of the mirror A is in a vertical line with the centre ofthe glass tube,
and consequently only one half of the air bubble is seen on the mirror; this
answers every purpose of the bubble, and leaves the sight clear through the
telescope. D is a thin piece of glass with a divided edge, forming the well-
known military distance measurer. It is placed on one side of the vertical
plane of the focus of the ocular lense L, and opposite the mirror. I propose
to combine this distance measurer with the mirror when required.
An important modification of this reflective principle of levelling is shewn
at Fig. 4, where the reflecting mirror presents a cylindrical surface; this
enables the mirror to be placed at an increased distance from the bubble;
but what is of still more importance, the mirror inay be placed at or near the
focus of the ocular lense, by which the length of the glass tube B may be
increased, and an air bubble of any degree of sensibility obtained; since by
varying the radius which describes the surface of the mirror, the apparent
length of the bubble, as represented by reflection on the mirror, can be
reduced to any desired si ze. As by this arrangement the position of the
spider's web or silk thread usually placed across the field of view at the focus
of the ocular leuse is occupied by the mirror, a reticule of glass, with a
diamond-drawn line across it, is substituted. Fig. 5 represents a cross section
of Fig. 4; the same letters of reference_referring to similar parts, as in the
Figs. 1 and 2..
Fig. 6 shews a sketch of an arrangement of mirrors, by which angles
may be measured between two fixed points, either by the horizon or spirit
level, both being reflected on the mirrors m, m³, while the objects observed
are seen on the mirror o. In this case the mirrors m, m³, would be of the
form shewn at Fig. 7. This reflective principle, in combination with a liquid
level, can be applied in a variety of forms and multiplication of the reflectors,
to all instruments where a level is required, or where angles are required
to be measured between two fixed points, or from the horizon, or a true
level.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said William Barrie in the Great Seal Patent Office on the
7th July 1856.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
BARRIE, of Maida Hill, London, in the County of Middlesex, Commander
R.N., send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Ninth day of January, in the year of our Lord
One thousand eight hundred and fifty-six, in the nineteenth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said William Barrie, Her special licence that I, the said William Barrie,
my executors,administrators, and assigns, or such other as I, the said William
Barrie, my executors, administrators, and assigns, should at any time agree
with, and no others, from time to time and at all times thereafter during the
terin therein expressed, should and lawfully might nake, use, exercise, and
vend, within the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention, communicated to me by a foreigner
residing abroad, for "AN IMPROVED REFLECTIVE LEVELLER," upon the condition
(amongst others) that I, the said William Barrie, by an instrument in
writing under my hand and seal, should particularly describe and ascertain
the nature of the said Invention, and in what manner the same was to be
performed, and cause the same to be filed in the Great Seal Patent Office
within six calendar months next and immediately after the date of the said
Letters Patent.
NOW KNOW YE, that I, the said William Barrie, do hereby declare the
nature of the said Invention, and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement (that is to say):-
"
An instrument for the use of navigators, surveyors, engineers, and other
persons who require the use of a levelling apparatus. It consists in an
improvement upon the hand leveller con trived by Romershausen, wherein a
mirror placed in a tube at an angle of forty-five degrees to the axis of the
tube, reflects one half of the air bubble of a spirit level placed above the
mirror, so that by looking through the tube the observer sees in one direction
the air bubble reflected upon the mirror, the thread, or spider's web, or
reticule across the tube, and the landscape beyond. By bringing the centre
of this reflected bubble in line with the reticule the instrument is levelled.
This Invention consists firstly, in the application and adaptation of the

page_text: above described reflecting instrument to telescopes where lenses are employed,
in order that the reticule may be placed in the focus of an ocular lens"; "a
longitudinal section of such an instrument is shewn on the accompanying
Sheet of Drawings at Fig. 11.; where E represents the ocular lens; B, the
spirit level; and b, the air bubble, reflected at a, upon the mirror A, which
may be either of glass or metal, the latter being preferable. The mirror A is
placed with its upper surface at an angle of forty-five degrees with the axis of
the tube, and the inner edge of the mirror a little on one side of the axis, as
shewn in Fig. IV., which is a cross section of the instrument between the
ocular lens and the mirror; the object of moving the mirror thus to the loft
is to leave the field of view clear to the observer. The spirit level B lies
parallel with the telescope tube, but is also a little on one side of a vertical
plane, cutting the axis of the telescope; the centre of the level is thus in a
vertical plane with the inner edge of the mirror, which consequently reflects
one half of the bubble. The level is adjusted in its parallelism by the springs,
and set screw shewn detached at Fig. III.. The well-known military
distance measurer may be also used with this instrument, and placed opposite
to the mirror, as shewu at D, Fig. IV. By the above-described instrument
it will be observed that the reticule facross the tube C can be placed in the
focus of the ocular lens E, but the mirror A must be between the lens and its
focus. To obviate this defect, a modification of the instrument is shewn at
Fig. V., which is a similar section to Fig. IV.; but the centre of the mirror,
and consequently the centre of the reflected bubble, is placed in the focus of
the lens E, and the plane of glass D, forming the distance measurer, is carried
across the field of view, with a fine diamond-drawn line across it, in lieu
of the spider's web or thread forming the reticule.
An arrangement for fixing the image of the reflected bubble more distinctly
with respect to the reticule is shewn at Fig. VIII., which represents the spirit
level detached. Across the centre of the glass tube a band of metal c is
passed, so as to hide a portion of the bubble; the band c may be placed
across the top or the bottom of the glass tube, or across both.
An important modification of the instrument consists in making the mirror
of a plano-cylindrical form, with the cylindrical surface presented opposite to
the spirit lovel, as shewn in Fig. II. This form of mirror contracts tho
apparent length of the reflected bubble to any desired size, by varying the
amount of curvature of the mirror, so that the reflected bubble may be made
to appear the thickness only of the reticule; and much greater accuracy thus
obtained in levelling the instrument. It also euables the spirit level to be
placed at any desired distance from the axis, of the telescope. Another

page_text: advantageous circumstance is, that an image reflected by a cylindrical mirror
in the direction perpendicular to a parallel with the axis of the cylinder
is distinctly seen at the distance of the reflection from the eye, just as if
the object stood at the position of the reflected image instead of its own in-
creased distance. This allows an ocular lens of any focus to be used, and the
mirror to be placed at the focus of the lens employed, by. which we gain
an increased length of spirit level, and greater sensibility of the bubble.
It will be obvious this instrument will be applicable to a variety of
scientific purposes. Fig. 1. represents its adaptation to the sextant, to dispense
with the use of the horizon at sea. At Fig. VII. an arrangement is shewn
for the threefold purposes of levelling, measuring elevations, and measuring,
as with the sextant, angles between any two given points. For that purpose
let the mirror m¹ go quite across the first tube T, and cut out the centre of
the mirror, as shewn in the separate view Fig. VI. ; have a second objective
lens o, and a second mirror m, to reflect the horizon, and you will then have
the horizon reflected in front of the eye upon the mirror m² at a¹, and the
reflected bubble (when required to be used) upon the opposite side of the
mirror mata, while the field of view will be clear between the two reflec-
tions to observe the object reflected upon the outer mirror p. This outer
mirror p must of course be attached to a radius arm moving along a gradu-
ated are similar to the sextant, to read off the angle between the two objects
observed, or the angle of elevation, or the altitude of the object.
I claim the application of the bubble reflector to all instruments of
observation wherein lenses are employed, and the use of mirrors with
curved surfaces, for reflecting and varying the apparent size of the reflected
bubble, as described, in all geodetical, astronomical, and other instruments of
observation.
In witness whereof, I, the said William Barrie, have hereto set my
hand and seal, this Seventh day of July, in the year of our Lord One
thousand eight hundred and fifty-six.
Witness,
EDWARD JAMES POWELL.
WILLIAM BARRIE. (L.S.)