AN IMPROVED PROTRACTOR OR INSTRUMENT FOR ASCERTAINING ANGLES OF ELEVATION AND DEPRESSION
Year: 1876

page_text: LETTERS PATENT to Willoughby Smith, of Wharf Road, in the County of
Middlesex, Electrician, for the Invention of "AN IMPROVED PROTRACTOR OR
INSTRUMENT FOR ASCERTAINING ANGLES OF ELEVATION AND DEPRESSION."
A communication from abroad by Philip Bell Baldwin, Lieutenant, R.E.,
resident at Bangalore, Mysore, India.
Sealed the 12th January 1877, and dated the 5th October 1876.
"
PROVISIONAL SPECIFICATION left by the said Willoughby Smith at the
Office of the Commissioners of Patents on the 5th October 1876.
WILLOUGHBY SMITH, of Wharf Road, in the County of Middlesex, Electrician.
AN IMPROVED PROTRACTOR OR INSTRUMENT FOR ASCERTAINING ANGLES OF ELEVA-
TION AND DEPRESSION." A communication from abroad by Philip Bell Baldwin,
Lieutenant, R.E., resident at Bangalore, Mysore, India.
The object of this Invention is to provide an instrument of great simplicity of
construction and of extreme portability, by the use of which angles of elevation
and depression can be accurately ascertained.
The instrument consists of a rectangular strip of wood, bone, or ivory, or of a
plate of metal or similar material, upon the edges of which is marked the protractor
scale. Towards the bottom of the plate a rectangular recess or slot is formed, to
one end of which is hinged a correspondingly shaped piece of metal or other material
which exactly fits the slot. The rectangular piece is hinged at one end of the recess
or slot and has a tendency to open partially outwards imparted to it by means of a
spring or other arrangement, while at the other end à catch is fitted which will
retain it when closed. The face of this piece which closes like a lid into the slot
is provided with a mirror so as to reflect the degrees with which the back or face
of the slot is marked. At the bottom of the plate and at its exact middle a plummet
is suspended by a thread.
In using the instrument, the operator takes the plate in his hand and looks along
its lower edge at the object the angle of which is required, taking care that the
piece or lid is opened. In doing so the thread carrying the plummet passes between
the plate and the mirror face of the piece covering the slot; the mirror reflects the
thread and the scale written upon the back of the slot, and thus enables the angle
Price dl

page_text: to be read off the scale immediately. On the opposite side of the plate to that on
which the protractor scale is written, a scale of "shade" may be provided by which
approximate angles of gradients and inclines can be read off at the same time as the
angles of elevation or depression.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by the
said Willoughby Smith in the Great Seal Patent Office on the 5th April 1877.
WILLOUGHBY SMITH, of Wharf Road, in the County of Middlesex, Electrician.
"AN IMPROVED PROTRACTOR OR INSTRUMENT FOR ASCERTAINING ANGLES OF ELEVA-
TION AND DEPRESSION." A communication from abroad by Philip Bell Baldwin,
Lieutenant, R.E, resident at Bangalore, Mysore, India.
The object of this Invention is to provide an instrument of great simplicity of
construction and of extreme portability, by the use of which angles of elevation and
depression can be accurately ascertained.
The instrument consists of a rectangular strip of wood, bone, or ivory, or of a
plate of metal or similar material, upon the edges of one face of which is marked
the protractor scale. Towards the bottom of the plate on the opposite face a
rectangular recess or slot is formed, to one end of which is hinged a correspondingly
shaped piece of metal or other material which exactly fits the slot. The rectangular
piece being hinged has a tendency to open outwards to an angle of 45° from that
face under the action of a spring or other arrangement. At the other end of the
slot a catch is fitted which will retain the piece when closed. The inside face
of this piece which closes like a lid into the slot is provided with a mirror so as to
reflect the degrees which are marked on the back or face of the slot. At the
ordinary bottom of the plate and at its exact middle a plummet is suspended by a
thread.
In using the instrument the operator takes the plate in his hand and looks along
its bottom edge (which is for the purpose brought uppermost) at the object the
angle of which is required, taking care that the piece or lid is opened. In doing
so the thread carrying the plummet passes between the plate and the mirror face
of the piece covering the slot; the mirror reflects the thread and the scale written
upon the back of the slot, and thus enables the angle to be read off the scale imme-
diately. On the opposite side of the plate to that on which protractor scale is
written, a scale of "shade" may be provided by which approximate angles of
gradients and inclines may be read off at the same time as the angles of elevation
or depression.
The instrument above referred to is clearly represented in the annexed Drawings,
all of which show the back face of an ordinary protractor strip or plate A. Bis
the door or lid hinged at C so that it may open outwards to an angle of 45° degrees
under the action of a spring D, fastened in the slot or recess as in Figure 1, or be kept
closed as in Figure 2 under the catch or hold of a slide bolt E. F is a plummet
and G a cord by which the plummet is suspended from a central point near to
what for the purpose of this Invention becomes the upper part, but is in reality the
botton of the protractor proper, the scale lines of which are upon the opposite face
to that shewn.
The inner face of the door or lid B has a mirror within it as in Figure 3, and the
face of the recess has a portion of a protractor scale upon it, so that as an observation
is being made the observer, having set the instrument to the angle according to the
line of sight, can read the angle in the mirror by the reflection of the scale lines
from the recess and of the cord which crosses the line corresponding to the angle, as
will be understood by reference to Figure 3, which represents a broad plate for the
better distinction of the lines. H is a pocket or aperture for the reception of
the plummet when the instrument is out of use, the cord being wound round the
plate

page_text: Having now described the nature of the said Invention, and in what manner the
same is to be performed, I declare that I claim the instrument represented in the
annexed Drawings, composed of a protractor plate, in one face of which is, 1, a
recess with a scale; 2, a hinged lid containing a mirror; and, 3, a plummet and
line, the whole combined in the manner set forth, by which angles of elevation and
of depression can be ascertained as described.
In witness whereof, I, the said Willoughby Smith, have hereunto set my hand
and seals, this Fourth day of April, One thousand eight hundred and seventy-
seven.
WILLOUGHBY SMITH. (L.S.)