IMPROVE- MENTS IN THEODOLITES
Year: 1865

page_text: LETTERS PATENT to Bartholomew Parker Bidder, of Gateshead, in the
County of Durham, Mining Engineer, for the Invention of "IMPROVE-
MENTS IN THEODOLITES."
Sealed the 4th July 1865, and dated the 9th January 1865.
PROVISIONAL SPECIFICATION left by the said Bartholomew Parker
Bidder at the Office of the Commissioners of Patents, with his Petition,
on the 9th January 1865.
I, BARTHOLOMEW PARKER BIDDER, of Gateshead, in the County of Durham,
Mining Engineer, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN THEODOLITES," to be as follows:-
The chief parts of the ordinary theodolite are a telescope with spiral level
attached, a vertical arc for taking angles of altitude and depression, a horizontal
limb and compass for taking horizontal angles and the bearing of objects, and
two parallel plates with four conjugate screws by which the instrument is
adjusted.
Now my Invention consists in constructing theodolites with two telescopes
parallel to each other (one on each side of the vertical arc), the object glasses of

page_text: which are reversed. The spirit levels are placed on the parallel plates to the left
of the telescope, and are free from their movements. There is also a level im-
mediately above the two telescopes, so that when the instrument is set at zero
(and the conjugate screws are properly adjusted) it is perfectly level. It is
well known that in levelling the ordinary theodolite is not so correct as the
common level, and an instrument combining the accuracy of the level with
the speed of action of the theodolite has long been desired by engineers and
surveyors for ascertaining sections up steep acclivities; now, by means of my
theodolites with reversed telescopes the surveyor is enabled to take a foresight
without altering the telescope or the level after he has taken a back sight,
whereby the errors which now take place in resetting the instrument for the
foresight after the back sight has been taken are avoided. I do not confine
myself to any particular manner of fixing the telescopes.
The Invention is especially applicable to theodolites used for levelling in
mines.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Bartholomew Parker Bidder, in the Great Seal Patent Office
on the 8th July 1865.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, BARTHOLOMEW
PARKER BIDDER, of Gateshead, in the County of Durham, Mining Engineer,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Ninth day of January, in the year of our Lord
One thousand eight hundred and sixty-five, in the twenty-eighth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me,
the said Bartholomew Parker Bidder, Her special licence that I, the said
Bartholomew Parker Bidder, my executors, administrators, and assigns, or
such others as I, the said Bartholomew Parker Bidder, executors, adminis-
trators, and assigns, should at any time agree with, and no others, from time
to time and at all times thereafter during the term therein expressed, 'should
and lawfully might make, use, exercise, and vend, within the United King-
dom of Great Britain and Ireland, the Channel Islands, and Isle of Man, an
Invention for "IMPROVEMENTS IN THEODOLITES," upon the condition (amongst
others) that I, the said Bartholomew Parker Bidder, my executors or
administrators, by an instrument in writing under my, or their, or one

page_text: of their hands and seals, should particularly describe and ascertain the
nature of the said Invention, and in what manner the same was to be
performed, and cause the same to be filed in the Great Seal Patent Office
within six calendar months next and immediately after the date of the said
Letters Patent.
NOW KNOW YE, that I, the said Bartholomew Parker Bidder, do hereby
declare the nature of my said Invention, and in what manner the same is
to be performed, to be particularly described and ascertained in and by
the following statement thereof, reference being had to the Drawing hereunto
annexed, that is to say:-
The chief parts of the ordinary theodolite are a telescope with spirit level
attached, a vertical arc for taking angles of altitude and depression, a horizontal
limb and compass for taking horizontal angles and the bearing of objects, and
two parallel plates with four conjugate screws by which the instrument is
adjusted.
Now my Invention consists in constructing theodolites with two telescopes
parallel to each other (one on each side of the vertical arc), the object glasses
of which are reversed. There is a level immediately above the two telescopes,
so that when the instrument is set at zero (and the conjugate screws are
properly adjusted) it is perfectly level.
The accompanying Drawing is an elevation of a theodolite constructed
according to my Invention.
a, a, are two telescopes, one on each side of the vertical arc b, and parallel
to each other; the object glasses of the two telescopes are reversed, as before
mentioned. c is a spirit level above the telescopes. It is well known that
in levelling the ordinary theodolite is not so correct as the common level, and
an instrument combining the accuracy of the level with the speed of action of
the theodolite has long been desired by engineers and surveyors for ascertain-
ing sections up steep acclivities; now, by means of my theodolites with
reversed telescopes the surveyor is enabled to take a fore sight without altering
the telescope or the level after he has taken a back sight, whereby the errors
which now take place in resetting the instrument for the fore sight after the
back sight has been taken are avoided. I do not confine myself to any
particular manner of fixing the telescopes.
The Invention is especially applicable to theodolites used for levelling in
mines.
And having now described the nature of my said Invention, and in what
manner the same is to be performed, I declare that I claim constructing

page_text: theodolites with two telescopes as herein-before described and represented in
the accompanying Drawings.
In witness whereof, I, the said Bartholomew Parker Bidder, have here-
unto set my hand and seal, this Fifth day of July, One thousand
eight hundred and sixty-five.
B. P. BIDDER. (L.S.)