A LEVEL WITH MIRROR
Year: 1869

page_text: PROVISIONAL SPECIFICATION left by Romain François Bigot at the
Office of the Commissioners of Patents, with his Petition, on the
30th April 1869.
I, ROMAIN FRANÇOIS BIGOT, of Paris, Empire of France, Mechanician,
do hereby declare the nature of the said Invention for "A LEVEL WITH
MIRROR," to be as follows:-
My improved leveling apparatus consists of a looking-glass with plane
surface shown at A, B, Fig. 1 of the accompanying Sheet of Drawing
forming part of this Provisional Specification, this glass being placed in
a frame, and suspended in any suitable manner upon an elbow rod bent
at a right angle, and which is in its turn fixed to a cursor or slide M.
sliding along the rod which carries the instrument. Two screws P, P',
(Fig. 2) fix the elbow rod to the cursor M. This rod may be moved
up and down at will, so that the fiducial line or line of sight C, D,
may be always at the height of the zero on the vernier or graduated
scale V. It further carries a forked piece N, which grasps the glass
and keeps it from oscillating while leaving it great freedom of motion.
Only that part of the glass which is placed beneath the line of sight is

page_text: silvered; the upper part might even be dispensed with. The foot is
composed of a cylindrical rod or stem of wood, or of hollow metal of
from about 5 feet 10 inches to 6 feet 6 inches in height, and graduated
in inches or centimeters all round, beginning at about 39 inches from its
base. The elbow rod which upholds the looking-glass is fixed to the
cylindrical rod by means of a socket or collar provided with a regulating
screw, which permits its being raised or lowered at will. The foot is
held in a vertical position by means of a moveable tripod. Lastly, a
small vernier V placed above the socket or collar permits the valuation
of fractions of inches or of centimeters. The sight used with this appa-
ratus is simply an ordinary one, with this difference that the latter is
moveable, whereas that which I use remains fixed at a height determined
by the elevations or differences of level to be calculated.
My apparatus will serve for simple or compound leveling, tracing
curves, and settling inclines for railroads, irrigation, or other works.
The apparatus is used as follows:-The person holding the sight or
leveling staff is placed with it at a suitable distance from the apparatus,
and when by moving the apparatus along its rod the operator has set
the line of sight he at once sees the difference of level on the graduated
rod, without being obliged to apply to the staff holder, often too far off
and sometimes too ignorant to give him the information. The sight is
taken by bringing the pupil of the eye, which is then reflected in the
looking-glass, on the sight line C, D, and at the same time on the fiducial
line of the staff; the looking-glass being vertical the line of sight is
perfectly horizontal, and easily gives the difference of level. To guide
the operator in taking the level four horizontal arms are placed two and
two on each side of the looking-glass, and united by two wires D, D¹,
placed in front of the fiducial line C, D.
Fig. 4 represents an apparatus which may also be fixed on the foot or
stock of the level, and serve to measure inclines and elevations. The
dimensions of the vertical rod and of the shifting alidade may vary.
The verticalness is obtained by means of a spirit level placed on a shelf
forming part of the apparatus.