An Improved Surveying Instrument.
Year: 1893

page_text: Date of Application, 23rd Jan., 1893
Complete Specification Left, 19th Oct., 1893-Accepted, 25th Nov., 1893
PROVISIONAL SPECIFICATION.
An Improved Surveying Instrument.
I, JAMES HENDERSON, Civil and Mining Engineer, Member of the Institution of
Civil Engineers, residing at Dalvenie near Truro, Cornwall, with offices at
31 Lemon Street, in the said City of Truro, do hereby declare the nature of this
invention to be as follows: :-
My invention relates to an instrument for surveying according to the plane table
method, this instrument being so arranged that it retains a record of the directions
of the lines of survey, which lines can afterwards be readily transferred to a
plan.
The improved instrument consists of a disc mounted on a tripod stand with
suitable adjusting screws for levelling. On this disc is temporarily fixed a sheet
of celluloid or other like material on which pencil lines and marks can be made,
the sheet having marked on it a number of circles concentric with the centre of
the disc. Round the centre pin of the disc can revolve an alidade having one of
its edges, the fiducial edge, which coincides with a diameter of the disc, notched at
points corresponding with the circles drawn on the celluloid. The alidade, which
can be clamped in any position, is provided at each end with a sight, one of which
may be a vertical slot graduated, so that, while sighting for horizontal direction,
the elevation may also be observed. For more accurate sighting for elevation, a
graduated semicircle is fixed on the alidade, and the sights are fixed on a vertical
radial arm which can be turned round the centre of the semicircle.
Operations with the instrument, for which preferably three tripods are employed
in a survey, are carried on as follows. The alidade being sighted backwards for
the first line and clamped, the two lines are drawn along the fiducial edge where it
crosses one of the annular spaces between the concentric circles, and a number or
other mark is made to distinguish this line of survey. The alidade is then sighted
forward and the direction of the second line is similarly marked. The instrument
is then removed with its alidade still clamped to the tripod in front and sighted
back to the tripod from which it was taken; the alidade is then unclamped and
sighted forward for a fresh line which is marked. Thus a series of lines of
direction are marked on the annular spaces of the celluloid, among these a north
and south line taken by a compass applied to the alidade at any part of the survey.
For plotting the survey, the sheet of celluloid is removed from the disc and
temporarily fixed on the paper; then by a parallel ruler the various lines of
direction are transferred to any part of the paper, the lengths of the lines being
determined by the measurements noted during the survey.
Dated this 23rd day of January 1893.
ABEL & IMKAI,
Agents for the Applicant.
COMPLETE SPECIFICATION.
An Improved Surveying Instrument.
I, JAMES HENDERSON; Civil and Mining Engineer, Member of the Institution
of Civil Engineers, residing at Dalvenie near Truro, Cornwall, with offices at
31, Leinon Street, in the said City of Truro, do hereby declare the nature of this
invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
My invention relates to an instrument based on what is known as the plane-table

page_text: system of surveying, by means of which enclosed and open traverses, on the surface
or underground, can be effected and subsequently laid down on paper with great
rapidity, facility and accuracy. Unlike the plane table, however, it is not intended
that this traverse instrument should be used for plotting the survey in the field, a
process involving many great objections, but this is readily done afterwards in the
drawing office, with the aid of a parallel ruler and scale.
The instrument has a circular table mounted on a tripod stand, with the usual
adjusting screws, and an alidade with an ordinary "sight" at each end, revolving
round a fixed centre pin.
Upon the face of the table, a disc of celluloid, or other suitable material, is
securely attached, by means of several small screws, over which the alidade,
having a groove to clear them can travel freely. Celluloid is preferred as the
material of the disc as it requires no protection from weather, and does not
"buckle" or become deformed when wetted.
This disc is divided into a number of concentric rings, slightly scratched, or
grooved or pencilled on the celluloid, and the fiducial edge of the alidade is also
thus divided with a small semicircular notch at each annulus, for the purpose of
figuring or lettering the line observed and pencilled on the disc.
The object of these concentric rings, is to allow of separate surveys being
accomplished on one disc without overcrowding of direction lines in any particular
part of the disc.
By means of ordinary clamping screws, the table carrying the celluloid disc
can be clamped to the stand, and the alidade with its sights to the table when
required.
Fig. 1 of the accompanying drawings is a perspective view of the instrument,
Fig. 2 shews a modified construction with graduated semicircle for the accurate
measurement of vertical angles; Fig. 3 is a vertical sectional view of the
instrument shewing a portion of the tripod stand in side elevation and Fig. 4 illustrates
the mode of marking the lines on the annular divisions of the disc on the table.
A is a metal table secured in the usual manner to a tripod stand B, and levelled
by the aid of a small spirit level. C is the celluloid disc, divided into five
concentric rings 1, 2, 3, 4, 5 which are slightly scratched or pencilled upon it; D is
a small holding down plate for securing the disc, which is also secured at the
periphery by screw pins E. F is the alidade, having a half round or angular
notch at the middle, fitting against a centre pin G, which forms the centre
pivot round which the alidade turns. On the bevilled fiducial edge of the alidade
which coincides with a diameter are marked divisions corresponding to the
divisions 1, 2, 3 &c. of the disc C, and at these divisions half round or angular
notches are formed in the bevelled edge to allow of suitable marks being made
opposite the lines drawn on the disc. HH' are respectively the leading and back
sights attached by hinge joints to the lower frame I of the alidade, which is
provided with screws J for clamping it upon the table.
The instrument is worked as follows:-
It is set on its stand B and levelled by aid of a fixed or portable spirit level, and
the alidade F is sighted (by a back sight) on the starting point of the survey, and
both the alidade and the table are securely fixed by their respective clamps J
and K.
The direction of this first line of the survey is then marked with a finely pointed
pencil on one annulus of the disc, at two points equidistant from the centre, and
lettered, or figured, within the notch cut in the edge of the alidade.
The alidade is then unclamped and sighted to the forward stand, or tripod, and
clamped (three tripods being recommended for properly conducting a traverse)
and the direction of the second line of the survey is marked on the annulus as
before.
The instrument is then removed from its stand and fixed, with the alidade still
clamped, on the forward stand and sighted back to the tripod which it formerly
occupied, and clamped.

page_text: This being done, the alidade is unclamped, sighted to another forward stand;
and again clamped and the direction of the third line of the survey is marked, and
figured, on the disc. This is repeated throughout the traverse, the surveyor.
recording in his book the lengths of the several lines, with offsets in the
ordinary way.
The magnetic meridian is taken at any convenient spot in the course of the
traverse by means of a "trough" compass placed temporarily against the back
edge of the alidade; the line, thus obtained is pencilled on the disc, establishing
the polarity of the whole of the survey.
The same disc on its table can be used on any disconnected part of a survey, by
again placing the trough compass against the alidade, clamped on the previously.
pencilled north line, the table being moved until the needle points to the north.
The leading direction of each line is given by simply making a half arrow
against the line before moving the alidade as at Fig. 4 thereby showing the course
or direction of line 2.
The fiducial edge of the alidade should always be to the surveyor's right hand,
he facing in the direction of the traverse line, so as not only to afford greater
facility for drawing, and figuring, the lines on the disc, but also to prevent any
chance of misplacing the guiding half arrow referred to.
In order to use the instrument on hilly ground, the sights at each end of the
alidade, are marked in degrees up to 25° as indicated at L Fig. 1, so that by
looking over the top of the back sight and getting the forward object in line with
one of the divisions, the angle of declination can be read and recorded.
Where greater accuracy as to vertical angles is required, as in diagonal shafts of
a mine, a semicircle is attached to the alidade, as shown at M Fig. 2, by which the
angles can be read to minutes, as in the ordinary theodolite, or miner's dial.
For this purpose the ordinary sights H H₁ are removed, and the graduated
semicircle M is screwed on the alidade F. N is the pivotted arm with sights,
vernier, and level as in a theodolite and like instrument. Or a telescope can be
substituted for the sights when required, and, in order that the telescope may be
used for taking a back sight without having to turn the alidade half round, I
prefer to make the telescope reversible by pivotting it on an axis radial to the
semicircle on which it is mounted.
-
The observations are plotted in the drawing office in the following manner.
One or more meridian lines having been drawn on the intended plan, the disc is
removed from the instrument and placed with the north line which was marked on
it in the field, in coincidence with a meridian in which position it is held by a
weight. A rolling parallel ruler is then applied to each line of the survey
appearing on the disc, and a corresponding line is drawn on the plan. In a large
survey the disc can be moved to any of the meridian lines the disc practically
serving as an accurate protractor.
For further reference, the disc itself may be kept marked with the name and the
date of the survey, or the magnetic bearings of the lines may be read off and
entered in the field or survey book, whereupon the celluloid disc can be washed
clean for use in another survey.
For rapid triangulation the instrument can be used as follows: A suitable base
line having been measured, the instrument is set up at the ends of the line, and the
bearings of the distant points are marked on the disc, the work being subsequently
plotted in the office to any desired scale.
The instrument, being very portable, requiring no skilled manipulation, no
reading of angles and no subsequent calculation, can be used with advantage for
military purposes, as it can be worked in all weathers, and the salient points of the
country, the position of the enemy or other objects can subsequently be mapped
with speed and accuracy.
It could also be used as a range finder, a base line being measured and a pair of
the instruments being worked simultaneously at both ends, the range of even a
moving object could be ascertained with approximate accuracy.

page_text: Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. In a traverser for surveying purposes, the combination with a table, adapted
to be fixed on a stand, of a disc of celluloid or the like temporarily secured on the
table and marked with concentric annular divisions, an alidade pivotted to the
centre of the table and having divisions and notches on its fiducial edge to suit
the divisions of the disc, a sight at each end of the alidade, and means for clamping
the table and alidade, substantially as described.
2. In a traverser for surveying purposes, the combination with a table adapted
to be fixed on a stand, of a disc C of celluloid or other suitable waterproof material,
having marked thereon concentric circular divisions for the reception of lines
marked thereon by the aid of an alidade, substantially as described.
3. In a traverser for surveying purposes, the combination with a table A adapted
to be fixed on a stand, of a disc C of celluloid or the like, having concentric
circular division lines marked thereon, an alidade F pivotted to the centre of the
disc and table and having divisious with notches corresponding to the divisions of
the disc, sights H H' detachably mounted on the ends of the alidade so that on the
removal of the sights, a graduated semicircle with pivotted arm carrying sights or
a telescope and vernier for measuring angles may be secured to the alidade,
substantially as described.
Dated this 19th day of October 1893.
ABEL & IMRAY,
Agents for the Applicant.