IMPROVEMENTS IN AND ADDITIONS TO THEODOLITES AND OTHER SIMILAR INSTRUMENTS TO FACILITATE THEIR USE FOR MEASURING AND ASCERTAINING DISTANCES
Year: 1876

page_text: LETTERS PATENT to James Wallis, of Cranmer Road, Brixton Road, in tho
County of Surrey, Optical and Mathematical Instrument Maker, for the
Invention of "IMPROVEMENTS IN AND ADDITIONS TO THEODOLITES AND
OTHER SIMILAR INSTRUMENTS TO FACILITATE THEIR USE FOR MEASURING
AND ASCERTAINING DISTANCES."
aled the 7th November 1876, and dated the 9th May 1876.
PROVISIONAL SPECIFICATION left by the said James Wallis at the Office
of the Commissioners of Patents on the 9th May 1876.
JAMES WALLIS, of Cranmer Road, Brixton Road, in the County of Surrey,
Optical and Mathematical Instrument Maker. "IMPROVEMENTS IN AND ADDITIONS
TO THEODOLITES AND OTHER SIMILAR INSTRUMENTS TO FACILITATE THEIR USE FOR
MEASURING AND ASCERTAINING DISTANCES."
This Invention relates to improvements in and additions to theodolites and other
similar instruments to facilitate their use for measuring and ascertaining distances,
and consists in fitting a disc prisin in a frame between the eye piece and the object
glass, such frame having a motion upon a hinge joint under the control of an
eccentric pin, which is capable of being turned by a button head on the outside
that the prism can be moved or turned to one side out of the optical axis of the
telescope to enable the instrument to be used for ordinary surveying purposes, and
be brought or turned into or across the optical axis to enable the instrument to bo
used for measuring and ascertaining distances. The eccentric pin works in a slot
formed in a barrel portion of a piece of tubing, to which the tail end of the hinge is
attached, and as the tube is moved to and fro by the rotatory motion of the
button head the prism frame turns upon its hinge. I arrange a double ended spring
to a fixed part of the telescope that its free ends may bear upon pins of the prism
frame, and exert a power to retain it in position whether within or outside of the
optical axis.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said James Wallis in the Great Seal Patent Office on the 9th November
1876.
"
JAMES WALLIS, of Cranmer Road, Brixton Road, in the County of Surrey,
Optical and Mathematical Instrument Maker. IMPROVEMENTS IN AND ADDITIONS
TO THEODOLITES AND OTHER SIMILAR INSTRUMENTS TO FACILITATE THEIR USE FOR
MEASURING AND ASCERTAINING DISTANCES."
This Invention relates to improvements in and additions to theodolites and
other similar instruments to facilitate their use for measuring and ascertaining
distances, and consists in fitting a prism in a frame between the eye piece and the
object, glass, such frame having a motion upon a hinge joint under the control of an
excentric pin, which is capable of being turned by a button head on the outside
that the prism can be moved or turned to one side out of the optical axis of the
telescope to enable the instrument to be used for ordinary surveying purposes, and
be brought or turned into or across the optical axis to enable the instrument to be
used for measuring and ascertaining distances. The excentric pin works in a slot
formed in a barrel portion of a piece of tubing, to which the tail end of the hinge is
attached, and as the tube is moved to and fro by the rotary motion of the button
head the prism frame turns upon its hinge. I arrange a double ended spring to n
fixed part of the telescope that its free ends may bear upon pins of the prism frame
and exert a power to retain it in position whether within or outside of the optical
axis.
"
The improvements above set forth are clearly represented in the annexed
Drawings, which show a mathematical instrument in Figure 1, which I call the
euperimeter," with which and without change of position or a known base line
distances of distant objects may be determined in a few minutes to as high a degree
of accuracy as can be obtained by actual measurement.
T, I, is the optical axis, line of collimation, or axial line of the telescope. This
line passes through the optical centre of the object glass T, and the intersection of
the cross wires at the focus above Q.
Bis
A is a milled head employed in turning the prism P into and out of use.
a graduated circle connected with the prism P; C is a clamp screw for clamping
the circle B, which has only power to move through an are of a quadrant; 1) is the
slow motion screw employed to set exactly the wires of the diaphragm on a distant
object; P shows the position of the circular or other shaped prism inside the telescope
when in use.
Figure 2 is a detached view of the hinged prism in its place when distances are
being measured; and Figure 3 shows the prism thrown back or open as out of use.
S, Figure 1, is a portion of, or say, five feet of a staff pointed out by the diaphragm
wire in moving B from stop to stop, which turns P through an arc of 90 degrees;
hence the distance of S from P is 500 feet.
From the sketch, Figure 1, it will be readily perceived that the instrument or
cuperimeter is similar to an ordinary transit theodolite, with an additional graduated
circle B, whose plane is perpendicular to the line of collimation T, I, which passes
through the centre of B. The perpendicular distance measured along the line T, I,
between the planes of the parallel circles that pass through the centre of B and the
centre of the prism P in position remains a constant quantity, and the distance from
the centre of the prism P in position to the middle of the cross wires of the
diaphragm is a constant quantity also, and may be aptly termed the base of the
ouperimeter.
The prism P inside the telescope is attached to B, and as B is turned from 0 to
00 degrees, on the optical axis of the telescope P is turned on the same axis in the
same way and to the same extent, but the perpendicular distance of the plane of P
from the plane of B is not altered by this motion, which is regulated by two stops,
one at 0 and the other at 90 degrees.

page_text: The position and refractive power of the prism P are so designed and so combined
with respect to the magnifying power of the telescope that when the prism is turned.
from 0 to 90 degrees, that is, from stop to stop, every foot of levelling staff shown
between the two positions of the diaphragm wire obtained by turning the prism
from stop to stop gives 100 feet of distance from the observer to the staff. Hence,
if a levelling staff be set up at 500 feet from the euperimeter an observer will find
when the instrument is adjusted and directed to the staff that by turning the
circle B from stop to stop the wire in the diaphragm is apparently refracted by tho
prism 5 feet up or down along the staff.
If an observer finds that by turning the circle B 90 degrees from stop to stop,
and that the wire of the diaphragm appears to move over 10.25 feet of staff, then
the distance of tho staff from the observer is 10 25 feet, or 10.25 x 100; thero-
fore, if a lovelling staff can be placed and observed near or at any distant object,
the distance of such object from the instrument can be instantly found without
calculation, the uso of tables, and even without feading off the instrument.
When the euperimeter is employed to measure angles the prism P is turned
aside out of the optical axis. In this position the prism is out of use, and then
nothing interferes with the direct collimation of the telescope. When the angles
are measured. tho prism P may again be brought into place or position for measuring
distances by merely turning the milled head A half round. One arc on B, by
which the range of the prism P is made to measure, is divided into half degrees,
and by the use of a vernier it subdivides the same arc into minutes.
On B there is another set of divisions, but not equal divisions. These divisions
subdivide the vertical and horizontal range of the prism into 100 equal parts without.
the use of a vernier. When necessary a higher degree of refinement can be applied.
However, 100 equal parts have been found very convenient in practice, for,-
One of these parts is equal to 0100 of a foot at 100 feet distanco