IMPROVEMENTS IN LEVELS THEODOLITES AND SUCH LIKE INSTRUMENTS OF OBSERVATION "
Year: 1883

page_text: LETTERS PATENT to Horace Darwin of Cambridge in the County of Cambridge
for an Invention of "IMPROVEMENTS IN LEVELS THEODOLITES AND SUCH
LIKE INSTRUMENTS OF OBSERVATION
"
PROVISIONAL SPECIFICATION left by the said Horace Darwin at the Office
of the Commissioners of Patents on the 2nd October 1883.
HORACE DARWIN of Cambridge in the County of Cambridge "IMPROVEMENTS
IN LEVELS, THEODOLITES AND SUCH LIKE INSTRUMENTS OF OBSERVATION
"
In Levels, Theodolites and such like instruments of observation, it is necessary to
provide for movements of the parts while they keep their constant relation to each
other in respect of inclination. Thus, in shifting the lens, for the purpose of
focussing, its optical axis must remain constant; in turning the telescope of a
level round its vertical axis, the axis of the telescope must remain horizontal, and
in turning the telescope of a theodolite on either the vertical or the horizontal axis
on which it is mounted, or on both of them, these two axes must remain
perpendicular to each other. In order to maintain accuracy in these respects, I
apply to the shifting parts of the instruments a method of fitting and, bearing
which consists in effecting the fit by contact of four points on a truly cylindrical
or turned surface. Applying this method to a level, I turn the exterior of the
telescope tube truly cylindrical for at least a part of its length, sufficient for the
shifting of the lens for focussing, and I suspend the lens within the tube by a
stem which passes freely through a longitudinal slot of the tube and is attached to
a frame having four points bearing on the external cylindrical surface of the tube.
When the frame and lens are shifted to or fro the bearing of the four points of
the frame on the cylindrical surface ensures that the movement of the lens is in a
line accurately coinciding with the axis of the cylindrical tube. In a similar
manner I mount the telescope by four points bearing against a truly turned
surface of the upright post round which the telescope can turn, and by making one
or other of these points adjustable as a screw I can adjust the telescope so as to
bring its axis truly at right angles to that of the vertical post. Applying the
same construction to the horizontal axis of a Theodolite, I can, in like manner,
ensure true perpendicularity of the telescope tube to it, and of the two axes to
each other.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Horace Darwin in the Patent Office on the 26th March 1884.
HORACE DARWIN of Cambridge in the County of Cambridge. "IMPROVEMENTS
IN LEVELS, THEODOLITES AND SUCH LIKE INSTRUMENTS OF OBSERVATION
In levels, theodolites and such like instruments of observation, it is necessary
to provide for movements of the parts while they keep their constant relation to
each other in respect of inclination. Thus, in shifting the lens, for the purpose of
focussing, its optical axis must remain constant; in turning the telescope of a
level round its vertical axis, the axis of the telescope must remain horizontal; and
in turning the telescope of a theodolite on either the vertical or the horizontal axis
on which it is mounted or on both of them, these two axes must remain
perpendicular to each other. In order to maintain accuracy in these respects I
apply to the shifting parts of the instruments a method of fitting and bearing,
which consists in effecting the fit by contact of four points on a truly cylindrical
or turned surface. Applying this method to a level, I turn the exterior of the
telescope tube truly cylindrical for at least a part of its length sufficient for the
shifting of the lens for focussing, and I suspend the lens within the tube by a
stem which passes freely through a longitudinal slot of the tube, and is attached to
a frame having four points bearing on the external cylindrical surface of the tube.
When the frame and lens are shifted to or fro, the bearing of the four points of
the frame on the cylindrical surface ensures that the movement of the lens is in a
line accurately coinciding with the axis of the cylindrical tube. In a similar
manner, I mount the telescope by four points bearing against a truly turned
surface of the upright post round which the telescope can turn, and by making one
or other of these points adjustable as a screw, I can adjust the telescope so as to
bring its axis truly at right angles to that of the vertical post. Applying the
same construction to the horizontal axis of a Theodolite, I can, in like manner,
ensure true perpendicularity of the telescope tube to it, and of the two axes to
each other.
The accompanying drawings shew the application of the manner of fitting above
described to the object lens of the telescope of a level, and to the vertical post or
axis around which the telescope has to turn. Fig. 1 is a side view partly in
section, fig 2 is a plan, and figs 3, 4 and 5 are transverse sections on X, Y and Z
respectively. The tube T of the telescope, along a part of its length sufficient for
the movement of the frame F which carries the object lens L is turned truly
cylindrical externally. The lens L is attached to the frame F by a stud which
passes freely through a slot t cut in the tube, and the frame F has four feet f
which bear on the truly turned surface of the tube, so that as the frame is moved
to and fro longitudinally, the lens moves in a line always parallel to the axis of
the tube.
The post P or vertical axis around which the tube has to turn is also truly
turned cylindrical, and the tube T has four feet or studs bearing against the
cylindrical surface, namely the two feet p p projecting from a middle band of the
tube, and the two qq which are the ends of setting screws. By means of
the screws qq, the axial line of the telescope can be accurately adjusted so as to be
at right angles to the axis of the post P, and, the four feet p p and q q being kept
pressed against the surface of P by a spring S, the telescope, while it is turned
round P is made to preserve its perpendicularity thereto.

page_text: Having thus described the nature of my invention and in what manner the same
is to be performed, I claim in respect of Levels Theodolites and such like
instruments, :-
First Attaching the longitudinally shifting lens to a frame guided by four feet
bearing on the external cylindrical surface of the tube, substantially as herein
described.
Second: Mounting the circularly shifting tube or its frame, so that four feet
thereof bear on the cylindrical surface of the post or axis around which it turns
substantially as herein described.
In Witness whereof, I the said Horace Darwin have hereunto set my hand and
seal this twentieth day of March in the year of our Lord, one thousand eight
hundred and eighty four.
HODLOT DADWIN G
ITY ATTA
DADWINT
MOVICH