IMPROVEMENTS IN THE CONSTRUCTION OF LEVELLING INSTRUMENTS
Year: 1875

page_text: PROVISIONAL SPECIFICATION left by William Barnicoat at the Office
of the Commissioners of Patents, with his Petition, on the 9th
September 1875..
.
I, WILLIAM BARNICOAT, of 4, Smith Terrace, New Road, Battersea
Park, in the County of Surrey, Engineer, do hereby declare the nature
of the said Invention for “IMPROVEMENTS IN THE CONSTRUCTION OF LEVELLING
INSTRUMENTS," to be as follows:-
The object of this Invention is to provide a levelling instrument
which may not only be used in the same manner and for the same
purpose as the common spirit level, but also on an inclined plane for
checking or verifying the slope thereof, and which may likewise be
réversed for ascertaining the true level of a ceiling or any other surface
placed above instead of beneath the base of the instrument. To this
end I construct a levelling instrument in accordance with my Invention
by either of the two methods set forth in the following:-
By the first I provide a glass spirit tube enclosed within a metal tube
of the ordinary construction. Instead of attaching this metal tube to a

page_text: .
metal plate or similar appliance directly I furnish the one end of the
tube with an eye, lug, or fork piece fitted with a pin or axle, the central
_part of which rests within or upon a support fitted to a bottom plate of
-the-ordinary-kind,-so-that-the-tube_may_pivot_upon_the_pin_or_axle_as
its fulcrum. To the opposite end of the bottom plate I fit a circular
metal plate with degrees or other subdivisions marked thereon; and I
furnish the corresponding end of the metal tube with a pointer or other
suitable mark intended to denote any one of the subdivisions of the
divided circle, the tube being so adjusted that this mark comes opposite
the centre of the divided circle. When the axis of the tube is
parallel to the lower surface of the bottom plate I am enabled to apply
the instrument, to sloping or inclined surfaces, and by bringing the
bubble within the middle of the glass tube check or verify the angle at
which the surface is to be inclined, the level tube- itself acting in this
instance as a radial arm, which may be fixed by a set screw or other
similar appliance in the position required in each individual case.
.
By the second method I provide a bottom plate, to the middle of
which I fit a circular metal plate, divided in the same manner as in the
arrangement herein-before described. To the centre of this circle I fit
a hand or pointer, either in the manner in which this is done in clocks
and similar instruments, or else by furnishing the pointer or hand with
two conic points, one of which is held against the centre of the circle,
whilst the other rests against a support or pivot opposite thereto, and
fitted to the bottom plate of the instrument. To the bottom end of the
hand or pointer I fit or attach a counterweight in such a manner as to
compel the hand or pointer constantly to maintain its vertical position
while at rest, and_the_longitudinal_axis_of_the_hand being parallel to
the vertical-diameter of the divided circle, which itself is perpendicular
to the bottom plate, it follows that when the end of the pointer is
opposite the zero of the circle the instrument must always indicate a
true level; or if the pointer is opposite any one of the divisions it shews
that the surface to which the instrument is applied is inclined at the
angle denoted by such division.

page_text: By the construction herein described the spirit level is entirely
dispensed with, and it is obvious that in applying the bottom of the
plate to a ceiling or any other superposed surface the pointer will act in
the same manner as if the instrument rested upon a horizontal surface.