AN IMPROVED APPARATUS FOR DETERMINING DISTANCES
Year: 1877

page_text: LETTERS PATENT to George Anderson Vetch, of Edinburgh, in the County of
Mid Lothian, North Britain, for the Invention of "AN IMPROVED APPARATUS
FOR DETERMINING DISTANCES."
Sealed the 27th July 1877, and dated the 18th April 1877.
PROVISIONAL SPECIFICATION left by the said George Anderson Vetch at
the Office of the Commissioners of Patents on the 18th April 1877.
GEORGE ANDERSON VETCH, of Edinburgh, in the County of Mid Lothian, North
Britain. "AN IMPROVED APPARATUS FOR DETERMINING DISTANCES."
This Invention which relates to improvements in determining distances, and in
apparatus employed therefor, has for its object to effect the desired purpose with
accuracy, facility, and rapidity, and without the use of chains or other measures
ordinarily employed.
The apparatus, which is used in conjunction with a theodolite or other instru-
ment for taking angular observations, consists of a horizontal bar or rod mounted
on a convenient tripod stand, or other upright support, and having on its face a
graduated scale. A theodolite or other instrument of observation is placed at one
of two stations, the distance between which is required, and the horizontal bar at
the other, where it is adjusted in such a manner as to be at right angles to the line
of sight, and thus forms a base of an isosceles triangle, the sides of which correspond
with a given angle at the opposite station, and the graduations on the face of the
bar, which are included within the said sides, give the distance between the
stations.
When the distance is so great that the length of the horizontal bar is insufficient
to subtend the given angle this angle is halved, and the graduations of the bar then
represent twice their original value, and should this be found still insufficient the
angle is again halved, and the graduations of the bar represent four times their
original value, and so on, and according as the original angle is halved or divided
by four the number of observations is doubled or quadrupled, the sum of the
readings giving the measurement required; and any inaccuracy occurring in any
one observation is corrected by being distributed over the whole.
Instead of adopting a certain angle at the station of observation, as described,

page_text: the measurement between the stations may be determined by adopting a certain
length of the bar or rod as a constant base, and the angle which it subtends at any
given position when referred to a table of measurements computed for the purpose
will indicate the distance of that position from the station of observation.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said George Anderson Vetch in the Great Seal Patent Office on the
15th October 1877.
GEORGE ANDERSON VETCH, of Edinburgh, in the County of Mid Lothian, North
Britain. "AN IMPROVED APPARATUS FOR DETERMINING DISTANCES."
My said Invention which relates to an improved apparatus for determining
distances has for its object to effect the desired purpose with accuracy, facility, and
rapidity, and without the use of chains or other lineal measures ordinarily
employed.
The apparatus, which is used in conjunction with a theodolite or other instru-
ment for taking angular observations, consists of a horizontal bar or rod mounted
on a convenient tripod, stand, or other upright support, and having on its face a
graduated scale. A theodolite or other instrument of observation is placed at one
of two stations, the distance between which is required, and the horizontal bar at
the other, where it is adjusted in such a manner as to be at right angles to the line
the length of which is required, and supplies the base of a triangle, the other two
sides of which include a given angle at the opposite station. The graduations on
the face of the bar which are included within the said two sides give the distance
between the stations.
When the distance is so great that the length of the horizontal bar is insufficient
to subtend the given angle this angle is halved, and the graduations of the bar then
represent twice their original value, and should this be found still insufficient the
angle is again halved, and the graduations of the bar represent four times their
original value, and so on, and according as the original angle is halved or divided
by four the number of observations is doubled or quadrupled, the sum of the readings
giving the measurement required.
In taking these observations the upper horizontal limb of the theodolite remains
clamped after the laying off of each angle until the telescope is re-directed to the
zero or initial lines of the graduations of the rod, when the said upper limb is
released and a similar angle again laid off. By thus commencing the laying off of
each successive angle with the theodolite clamped at the reading of the previous
one, and completing the angular observations so that the theodolite at the last
observation gives the reading of the full angle, all intermediate errors of observa-
tion are cancelled, any errors due to the first setting of the theodolite plates and
the final reading alone remaining to affect the whole series of angles, which series
of angles may be multiplied to any extent with a view to increased accuracy.
Instead of adopting a certain angle at the station of observation, as described,
the measurement between the stations may be determined by adopting a certain
length of the bar or rod as a constant base, and the angle which it subtends at any
given position when referred to a table of measurements computed for the purpose
will indicate the distance of that position from the station of observation.
And in order that my said Invention may be properly understood, I now proceed
more particularly to set forth the system, mode, or manner in or under which the
same is or may be used or practically carried into effect, reference being had to the
annexed Sheet of Drawings, and to the letters and Figures marked thereon, that is
to say -
At Figures 1 and 2 on the appended Sheet of Drawings are represented front
elevations of one modification of my said Invention which may be used for

page_text: determining distances by both of the aforesaid methods, one of which I prefer to
designate as the direct method, in contradistinction to the other, in which the
distances are ascertained by observations on a given constant base, combined with
reference to computed tables of distances, as herein-after more fully specified.
The face of the rod or bar A is graduated throughout a portion of its length into
major divisions denoted thereon by the Figures I., II., and so forth, corresponding
to one, two, or more definite lineal measurements, say chains, and as many of these
as may be necessary or desired are subdivided into tenths, as indicated by the
Figures 1, 2, and so forth, and thereafter into hundreds, the last-named division
corresponding obviously to links. At the ends thereof the rod or bar A is furnished
with plates or targets a, a', Figure 1, of which one-half of each is preferably coloured
red, the other being white. The central divisional line o, o, of the target a is that
which marks the zero or initial line of graduation of the rod or bar, which latter is
mounted on a tripod stand B, as shewn, whereby it may be adjusted to become
level, and upon which it may revolve horizontally, a clamping screw b being provided
to fix it in any desired direction. On the upper side, and at the centre of the rod or
bar, are hinged sight plates c, c', having niches or grooves cut therein, and which
enable the rod or bar to be adjusted at right angles, with an imaginary line con-
necting the two stations, the distance between which it is desired to determine.
The method by which this distance is determined will be better understood by
reference to the diagram represented at Figure 3, in which the stations or pickets
are represented by the letters x and y, at the former of which a theodolite, or other
instrument for taking angular measurements, is placed, and the rod or bar A at the
latter.
The graduations on the face of the rod or bar A are calculated to subtend at the
point of observation a given angle. As shewn on the Drawings, they are
calculated for an angle of two degrees, being a convenient angle for practice. The
rod A having been adjusted horizontally by means of the tripod legs and screws,
and having been also adjusted by means of the sight plates c, c¹, so as to be at right
angles to the line y, x, is then clamped by the screw b aforesaid. The theodolite at
is now directed to the zero line of the rod, and the angle o, x, ol, equal to 2 degrees,
is laid off, when the reading at the point o' will indicate the horizontal measure-
ment of x, y, o, o', being the base of the approximately isoceles triangle o, x, o¹,
subtending at the point of observation a an angle of two degrees, to which, as
5 aforesaid, the graduations on the rod are calculated.
In cases where the distance between the stations or pickets is so great that
the graduated rod or bar A would not suffice to subtend an angle of two
degrees, the angle o, x, o¹, is made equal to one degree; and the upper plate of the
theodolite being clamped, it is re-directed to o, when the upper plate is released
and moved round until the vernier indicates two degrees from the commencement
of the observations; the telescope of the theodolite being now re-directed towards
the base at y, and a second reading of the graduated base having been taken, the
sum of these readings on the rod give the desired distance. In the same manner a
still greater distance can be determined by again halving the angle o, x, o¹, (thus
5 reducing it to half a degree or thirty minutes), and doubling the number of observa-
tions, which in such case will be four in number, and so on.
The modification of my said Invention, illustrated at Figures 1 and 2, is, as afore-
said, also adapted for the determination of distances by adopting a definite length
of rod as a constant base, and for this purpose the rod may be either a single piece,
0 or with a view to convenience when being carried, it may be of composite con-
struction.
Figures 1 and 2 show a composite rod provided with two arms d, d, which when
the instrument is being used, as before described, are in the position shown at
Fig. 1, that is to say, in the hollow body of the rod or bar A; but when it is
5 desired to use the instrument as a constant base, these arms d, d', are extended
longitudinally, as seen at Figure 2, to the requisite length, where they are retained
by the action of the springs and pins e, e¹. At the extremities of these armis d, d, are

page_text: attached the targets T, T¹, coloured, as indicated, which are so made as to allow of
their upper and under portions being folded back, and thus enabling them to
be withdrawn into the body of the rod, as seen at Figure 1. The distances
between the centres of the targets T, T¹, being a constant base of an isoceles
triangle, the angle subtended by it at any given point, if referred to a table of
relative distances computed for the purpose, the distance between the stations
desired to be determined is at once ascertained. To secure accuracy, the angular
observations may be multiplied indefinitely, the readings in the theodolite for each
successive angle commencing where the previous one left off, by which method
preceding errors of reading, with the exception of the first setting of the theodolite
are cancelled as these observations progress, leaving only the errors due to the first
setting and last reading of the theodolite to affect the entire series. The constant
base may be of any suitable length.
At Figures 4 and 5 are represented a front view and plan respectively of another
modification of my said Invention, in which the rod or bar A is provided with
hinges D, whereby it may be readily folded or extended. It is adapted for both
the herein-before described methods of determining distances, and is provided with
graduations on the top corresponding with those on its front face, small holes being
pierced at each of the former, as scen more particularly in the enlarged view
Figure 8. The object of having these holes is that the targets, as herein-after
described, may be placed therein for observation when the graduations of the rod
cannot be distinctly seen through the telescope of the theodolite.
It is to be understood that the rod or bar A is intended to be mounted on a
stand similar to that shown at Figure 1, and is furnished at its centre with the sight
plates c, c¹, hinged at opposite edges of the rod. Of these sight plates one is for
adjustment of the rod at right angles when observing upwards, and the other when
observing downwards. The central block of the rod is checked or stepped to pre-
vent the contact of the faces of the several portions thereof when the rod or bar is
closed or folded, and the ends being bevilled at the back do not project beyond the
face of the central block.
When the distance between the stations is so great that the graduations on the
face of the rod cannot be distinctly seen by the observer at the opposite station, a
target T2 of the form seen at Figure 7 is inserted in the hole of the graduation to
which the reading extends, and in the determination of distances in which it is
necessary to multiply the number of observations, as aforesaid, the target T is
placed in that hole on the top surface of the rod, which is in the line of the telescope
of the theodolite when the first angle is laid off.
Successive observations are made by clamping at T², re-directing the telescope on
the initial line of the rod, and again clamping for another observation on T%; this
is continued until the final observation of the series is arrived at, when having
observed as before on the initial line and unclamped the upper plate of the
theodolite, instead of now observing on T2, the theodolite is set to the complete full
angle of which the previous ones have been fractions. A second target is here inserted,
and the sum of the readings at the first target plus that at the last gives the
required distance.
It will be observed that the final setting of the theodolite at the correct full
angle corrects the previous angles.
In order to allow one target to be inserted in a hole near to or adjoining that in
which another is placed the targets are provided with hinges, whereby they may
be folded down.
Towards the end of the rod or bar A, in the modification shown at Figs, 4 and 5,
are pivotted the targets T, T¹, which are moveable through an are of 90 degrees; and
when the bar is being used under the indirect method as a base of constant length
the targets are clamped by the screws m, m³, in the position shown on the Drawing.
The distance between their divisional centre lines constitutes the base to which the
table of measurements is calculated, and to this table the angles subtended by it at
the point of observation are referred, in order to ascertain the distance desired to be

page_text: determined between any two stations or pickets. When the rod is folded or closed
the targets T, T¹, are brought into a horizontal position, grooves or recesses being
cut in the face of the rod for their reception, as shown.
Figure 8 represents a back view of the rod when folded and adapted for use
for shorter distances by the direct method, as herein-before described with reference
to Figure 1.
The first division of Figures 1 and 6 and the first two divisions of Figures 2
and 4 are not graduated, such graduation not being necessary where the original
angle is capable of being subtended by the said divisions. In such cases distances
may be measured by adopting the first major division as the initial point on the
rod, and the angle thus falls more equitably on either side of the centre of the rod
or bar, but if desired this latter may be graduated throughout.
In adjusting the rod or bar to be level and to be at right angles, as af esaid,
great accuracy is not necessary in ordinary surveying, as with care th error
arising from imperfection in these respects is not appreciable, but the sight plates
are preferably dished or grooved on their upper faces to assist in the latter
adjustment.
Having now described and particularly ascertained the nature of my said
Invention, and the system, mode, or manner in or under which the same is or may
be used or practically carried into effect, I would observe in conclusion that what I
consider to be novel and original and therefore claim as the Invention secured to me
by the herein-before in part recited Letters Patent is,―
First. The horizontal rod or bar having one or more of its sides graduated or
divided in the manner shewn, or any mere modification thereof, used in conjunction
with a theodolite or other instrument of angular observation, whereby the portion
of the rod or bar subtended by a given angle at the point of observation indicates
the distance between any two stations or pickets, substantially as herein-before
described, and shown on the accompanying Sheet of Drawings.
Second. The adoption, arrangement, and construction of the horizontal rod or
bar for the purpose of affording a constant base, the angles substended by which
indicate, when referred to, a specially computed table, the distances between the
said base and the points of angular observation, substantially as herein-before
described and shown more particularly at Figures 1, 2, 4, and 5 on the accompanying
Sheet of Drawings.
In witness whereof, I, the said George Anderson Vetch, have hereunto set
my hand and seal, this Eleventh day of October, One thousand eight
hundred and seventy-seven.
GEORGE A. VETCH. (L.S.)