Improvements in Instruments for Measuring Distances, to wit, a Tangent Reading Tacheometer.
Year: 1895

page_text: Date of Application, 21st Oct., 1895
Complete Specification Left, 21st July, 1898-Accepted, 21st Oct., 1896
PROVISIONAL SPECIFICATION.
Improvements in Instruments for Measuring Distances, to wit, a
Tangent Reading Tacheometer.
GEORGE JOSEPH BELL, County Surveyor, The Courts, Carlisle, and
WILLIAM OLIVER SMITH, WILLOUGHBY STATHAM SMITH and GEORGE
KEITH BULLER ELPHINSTONE trading under the title of Elliott Brothers,
Electrical Engineers, at 101-102 St. Martin's Lane, London W.C. do herebý
declare the nature of this invention to be as follows:-
The improvements consist in the application of the manner of construction and
graduation, which permits any form of theodolite, or such like instrument, to be
used trigonometrically, as well as geometrically, to determine distances and
altitudes at one and the same operation, by reading to the fifth place of decimals,
directly from the tangent scale of the instrument, the tangent of the actual angle
observed. The radius of the instrument is 6.25 inches, or one hundred sixteenthis
from the centre of the axis of the vertical are to the surface of the tangent scale,
and may be considered as radius 1. The horizontal or tangent scale is 4 inches in
length, and is graduated into 64 prime divisions, which are numbered each way
from the centre to 32 = 1 of an inch, and those divisions aro again subdivided by
an unnumbered line and, of an inch.
To this scale a drum head is attached, in such a manner that one revolution of
the drum either to the right or left moves the scale just one of these unnumbered
divisions i.e. end of an inch, or 500. The drum is divided into 100 equal parts,
and by meaus of a vernier into 500, thus dividing a full division on the tangent
scale into 1,000 visible equal parts, therefore the finest reading of the scale is
equal to Tobooth of an inch. In the same way radius 1 = 6.25 inches, or 10ths. of
an inch, therefore the numbered divisions ou the tangent scale are boths of the
radius of the instrument, and can be measured by the drum and vernier to read to
the 100,000th. part of the radius = to 00001 = tangent 2-06256459, hence reading
the tangents of observed vertical angles directly from the instrument, to the fifth
place of decimals.
Having devised this accurate method of reading, we use a suitably arranged
sighting staff graduated to use as a distant base, and by this means we determine
with practically absolute accuracy, at one operation, the actual horizontal distance
of any given object, and its vertionl height.
Dated this 16th day of October 1895..
GEO. JOS. BELL.
WILLIAM O. SMITH.
WILLOUGHBY S. SMITH.
G: K. B. ELPHINSTONE.

page_text: Improvements in Instruments for Measuring Distances, to wit, a
Tangent Reading Tacheometer.
We GEORGE JOSEPH BELL of The Courts Carlisle in the County of
Cumberland, County Surveyor, and WILLIAM OLIVER SMITH, WILLOUGHBY
STATHAM SMITH, and GEORGE KEITH BULLER ELPHINSTONE all trading
together under the name and style of Elliott Brothers 101-102 St. Martin's Laue
in the County of London, Instrument Makers, 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 :-
The object of this invention is to combine with theodolites and similar surveying
instruments generally used geometrically; a method whereby such instruments
may be also used trigonometrically, in conjunction with a specially designed staff
to form its distant base.
The improvements consist in the application of the manner of construction and
graduation of the instrument and staff, permitting the determination of distances
and altitudes at one and the same oporation, by reading to the 5th place of
decimals, directly from the tangent scale of the instrument, the tangent of the
actual angle observed; and when the solar attachment is applied to the tangent
reading tacheometer, the meridian, longitude, latitude, and time are readily
determined in the ordinary manner.
Fig. 1 is a side elevation of the complete instrument, showing all the usual
adjustments but without the solar attachment, which can be fixed to the instrument
when desired.
Fig. 2 is n plan of the instrument with telescope T (Fig. 1) and its attached
parts removed from the upright supports K Fig. 1, to show the scale D (Fig. 2),
more clearly.
Fig. 3 is a view of a piece of the scale D (Fig. 2) shown for sake of clearness
twice full size.
Fig. 4 is a diagram illustrating the principle of the instrument.
The instrument as constructed and shown in Figs. 1, 2, 3, consists of a finely
graduated horizontal limb F, Fig. 1, with vernier plates, mounted on a fitted
centre adjustable by the foot screws G.
Mounted on limb F is a graduated tangent scale D Fig. 2, with attached divided
drum head A and vernier B; operated by thumb piere E.
Scale D can be read by means of the microscope C. Fig. 1, fitted at right angles
to the telescope T, with attached finely graduated vertical circle H, supported on
the uprights K; both the horizontal and vertical limbs being fitted with tangent
adjusting screws, clamping screws, levels, &c., also a sensitive magnetic needle in a
brass trough box I, Fig. 1, attached to the telescope T.
The radius of the instrument, (that is, the perpendicular distance between the
trunnion axis of the telescope T, Fig. 1, and the scale D) being taken as
100,000 equal parts, the tangent scale is graduated into such parts (read by the
microscope C,) 32,000 each way froin the centre, and 32,000 100,000 is equal
to 32,000 or the tangent of 17° 44' 41' which is the limit of the tangent scale.
Consequently, the instrument reads angles from 2-06256459 seconds of are
to 17° 44′ 41″, practically by stages of 2·06256459 seconds, au that, the greatest
error can only be one second.
The radius of the tachcometer may be 6.25 inches or 100 sixteenths from the
centre of the axis of the vertical arc of the instrument to the surface of the
tangent scale, and may be considered as radius 1. But the length of the radius
varies according to the size of the instrument, and is always treated as radius 1.

page_text: If the radius is 6.25 inches the horizontal and tangent scale is four inches in
length, and is graduated into 64 primo divisions, which are numbered each way
from zero, in the centre of the scale, to 32, (=1e of an inch), and these division3
are again subdivided by an unnumbered line of an inch.
For fine adjustment, this scale D is traversed by the drum head in such a
manner that one revolution of the drum, either to the right or left. moves the
scale just one of these unnumbered divisions i.e. 3 of an inch, or 500 divisions of
radius.
The spindle of the dram head is a fine threaded screw which pushes the scale D
(Fig. 2) forward when the drum is rotated in a right handed direction. The spiral
spring 8.(Fig. 2) brings the scalo D back when the drum is rotated in a left
hauded direction.
E (Fig. 1-2) is a milled head fixed to the drum A (Fig. 1—2) for rotating it.
The drum scale is divided into 100 equal parts, and by means of a vernier
into 500, thus dividing a full division on the tangent scale into 1000 visible equal
parte, therefore the finest reading of this drum scale by means of the vernier is
equal to Tedor of an inch. In the same way if radius 1 is equal to 6.25 inches, or
100 sixteenths of an inch, the numbered divisions on the tangent scale are roths. of
the radius of the instrument, and can be measured by means of the powerful
microscope C, fixed at right angles to the teloscope, & by the drum scale and
vernier to read to the 100,000ths. part of the radius, and 1+100,000 is equal
to 00001, the tangent of 2-06256459 seconds, hence reading the tangents of
observed vertical angles directly from the tangent scale of the instrument to the
fifth place of decimals.
The microscope C, when the telescope T has been moved in altitude, reads on
the scale D the tangent of the angle, the scale itself being then moved a fraction
of a division by the drum D to bring the fiducial line in the microscope into exact
coincidence with the nearest graduation of the scale.
Having devised this accurate method of reading the tangents of vertical angles,
we use as a distant base a staff with euitable targets placed thereon, capable of
being adjusted 10 ft. apart; and by this means we determine with practically
absolute accuracy at one operation, the actual horizontal distance of any given
accessible object and its vertical height.
In using the instrument on rising ground, sight the upper target first, because it
is the greater augle. In this position the instrument is clamped and the tangent
read by means of the microscope with the drum and vernier; perform a similar
operation on the lower target and subtract the less tangent from the greater, and
with this romainder, divide the 10 ft. space between the targets for the horizontal
distance; and for the vertical height, multiply the horizontal distance by the
tangent of the less angle.
On falling ground, sight the lower target first, because in this case it is the
greater angle; find the horizontal distance as previously directed, and the vertical
height is found by multiplying the horizontal distance by the tangent of the
greater angle.
•
The Ravy
line a. a. (Fig. 4) represents the surface of the ground to be surveyed.
The following formula is proof of the accuracy of the method of using the instru-
ment described in the specificntion :—

page_text: instruments being used trigonometrically, substantially as described with reference
to Figs. 1, 2, 3, & 4 of drawings.
(2) A combined target staff for using as a distant adjustable base for the
instrument.
(3) The instrument and staff substantially as described and illustrated.
Dated this 21st day of July 1896.
GEO. JOS. BELL.
WILLIAM O. SMITH..
WILLOUGHBY S. SMITH.
G. K. B. ELPHINSTONE.
GEO. JOS. BELL.
WILLIAM O. SMITH.
WILLOUGHBY S. SMITH.
G. K. B. ELPHINSTONE.