IMPROVEMENTS IN INSTRUMENTS FOR SURVEYING AND LEVELLING
Year: 1862

page_text: LETTERS PATENT to George Henry Birkbeck, of the Firm of Tongue
and Birkbeck, of 34, Southampton Buildings, Chancery Lane, in the
County of Middlesex, Patent Agents and Engineers, for the Invention of
"IMPROVEMENTS IN INSTRUMENTS FOR SURVEYING AND LEVELLING."-A com-
munication from abroad by Monsieur Germain Auguste Leroyer, Principal
of the Institute of Vincennes, in the Empire of France.
Sealed the 27th May 1863, and dated the 24th December 1862.
PROVISIONAL SPECIFICATION left by the said George Henry Birkbeck
at the Office of the Commissioners of Patents, with his Petition, on the
24th December 1862.
I, GEORGE HENRY BIRKBECK, of the Firm of Tongue and Birkbeck, of
34, Southampton Buildings, Chancery Lane, in the County of Middlesex,
Patent Agents and Engineers, a communication from Germain Auguste
Leroyer, Principal of the Institute of Vincennes, in the Empire of France, do
hereby declare the nature of the Invention for "IMPROVEMENTS IN INSTRUMENTS
FOR SURVEYING AND LEVELLING," to be as follows:-
This Invention has for its object the arrangement and combination of parts
so as to form a compound surveying instrument to be called a "level
graphometer square," which is capable of executing the various operations

page_text: which each of the above-named instruments is only capable of performing
separately.
This improved instrument is composed of a cylinder of brass or other suit-
able metal divided longitudinally with its axis into two equal parts, connected
together by a central pin or axis, thus forming two cross staffs, to each of
which "pinules" are hinged so as to fold down out of the way when out of
Between the two semi-cylindrical parts a dial or plate, having divisions
thereon, is fixed and used when the instrument is employed as a "grapho-
meter," the instrument in this case being mounted by means of a screw, pin,
or otherwise upon a suitable stand or support.
When the instrument is employed as a level it is suspended by a ring
attached to the upper end thereof, and it is accurately adjusted perpendicularly
by a moveable weight actuated by an adjusting screw attached to the lower end,
sight holes or openings are formed through the moveable semi-cylindrical part
of the instrument through which the divisions on the dial plate may be seen
and read off when required, a fine wire or thread being stretched across each
aperture in the direction of the line of sight. Flat plates connected by a
central pin or axis may be substituted for the semi-cylindrical parts before
described, by which the construction of the instrument will be simplified, but
its form will not be so elegant. The divisions on the dial plate are in sections
of five or other suitable number of degrees, so that the instrument acts not
only as a "square" (which in other respects it replaces very advantageously)
but it also admits of small angles being taken as with the "graphometer."
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said George Henry Birkbeck in the Great Scal Patent Office on
the 23rd June 1863.
TO ALL TO WHOM THESE PRESENTS SHALL COME, J, GEORGE
HENRY BIRKBECK, of the Firm of Tongue and Birkbeck, of 34, Southampton
Buildings, Chancery Lane, in the County of Middlesex, Patent Agents and
Engineers, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-fourth day of December, in the year of our
Lord One thousand eight hundred and sixty-two, in the twenty-sixth year of
Her reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said George Henry Birkbeck, Her special licence that I, the said

page_text: George Henry Birkbeck, my executors, administrators, and assigns, or such
others as I, the said George Henry Birkbeck, 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 term therein expressed, should
and lawfully might make, use, exercise, and vend, within the United King-
dom of Great Britain and Ireland, the Channel Islands, and Isle of Man,
an Invention for " IMPROVEMENTS IN INSTRUMENTS FOR SURVEYING AND LEVELLING,"
a communication to me from abroad by Monsieur Germain Auguste Leroyer,
Principal of the Institute of Vincennes, in the Empire of France, upon the con-
dition (amongst others) that I, the said George Henry Birkbeck, my executors or
administrators, by an instrument in writing under my; or their, or one of their
hands and seals, 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 George Henry Birkbeck, do hereby
declare the nature of the said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement thereof, that is to say :-
This Invention has for its object the arrangement and combination of parts
so as to form a compound surveying instrument to be called a "level-grapho-
meter square," which is capable of executing the various operations which
each of the above-named instruments is only capable of performing separately.
This improved instrument is composed of a cylinder of brass or other suit-
able metal divided longitudinally with its axis into two equal parts connected
together by a central pin or axis, thus forming two cross staffs, to each of
which "pinules" are hinged so as to fold down out of the way when out of
Between the two semi-cylindrical parts a dial or plate, having divisions
thereon, is fixed and used when the instrument is employed as a "graphometer,"
the instrument in this case being mounted by means of a screw, pin, or other-
wise upon a suitable stand or support.
use.
When the instrument is employed as a level it is suspended by a ring
attached to the upper end thereof, and it is accurately adjusted perpendicularly
by a moveable weight actuated by an adjusting screw attached to the lower end.
Sight holes or openings are formed through the moveable semi-cylindrical
part of the instrument through which the divisions on the dial plate may be
seen and read off when required, a fine wire or thread being stretched across
ench aperture in the direction of the line of sight. Flat plates connected by

page_text: also forms an excellent level, for whilst being suspended by the ring a point
may be taken or seen across the pinules c of the part A, in the direction of the
diameter A, B. The correctness of level of the instrument is ascertained by
looking first at a point between A and B and then between B and A, on
reversing the instrument. If in each case the sight comes to the same point
the instrument is level, if it is not level it is made so by causing the weight M,
to advance or recede by means of the screw N, after which it can be worked
with much certainty. Lastly, the three interior divisions repeated right and
left of the vertical diameter, and above and below the horizontal diameter, serve
to give the height and distances both accessible and inaccessible on land,
(without which it would be necessary to construct proportional figures) which
thus places these beautiful and useful operations within the reach of all.
a
For taking the heights if the instrument (after being well levelled and.
suspended either from a finger or from a fixed point) point is seen under an
angle of 45° the vertical height of this point above the horizontal line (which
is set off from the feet to reach the foot of the object of which the height is
sought to be obtained) is precisely equal to the distance which separates the
instrument from the object itself. However in measuring, when this distance
is measured it will give the height of the object required, to which height it
is necessary to add the height of the instrument from the ground. If a point
is seen at an angle of 26 degrees, then the distance will be equal to double
the height sought to be ascertained, to which distance it will be necessary to
add double the height of the instrument above the ground. But if it is not
possible to approach the object it must first be seen at an angle of 45° and
then at an angle of 26 which will allow of the height of the object being
ascertained though it be impossible to approach the base of it. Lastly, if an
object is seen at an angle of 63 degrees a distance is obtained equal to half
the height of the object, to which must be added half the height of the instru-
ment above the ground. It must be clearly understood that if the operator is
placed in a position more or less elevated than the base of the object of which
the beight is desired, it will be necessary to determine this difference of level
or height and to calculate this difference either by adding or subtracting accor-
ding to whether the point where the operator stands is above or below the object
of which the height is required.
For measuring distances accessible and inaccessible the instrument is placed
horizontally on a foot or stand by means of the screwed boss d, and the opera-
tion is exactly the same as for measuring heights excepting that it is not
necessary to refer to the height of the instrument above the ground. There

page_text: is thus obtained a base equal to the distance, the half distance, or the double
distance which is desired. This base is drawn by means of two or three small
poles or stakes. The dimensions of the instrument herein described and
shewn in the Drawing may be varied according to the desire of the user and
the purpose for which it is required.
In witness whereof, I, the said George Henry Birkbeck, have hereunto
set my
hand and seal, this Twentieth day of June, in the year of our
Lord One thousand eight hundred and sixty-three.
G. H. BIRKBECK. (L.S.).