CERTAIN IMPROVEMENTS ON A MICROMETER
Year: 1811

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS
WILLIAM STURGEON, of Howland Street, Fitzroy Square, in the County of
Middlesex, Esquire, send greeting.
WHEREAS His most Excellent Majesty King George the Third did,
by His Letters Patent under the Great Seal of the United Kingdom of Great
Britain and Ireland, bearing date at Westminster, the First day of April,
in the fifty-first year of His reign, give and grant unto me, the said Thomas
William Sturgeon, my exors, admors, and assigns, His especial licence, full
power, sole privilege and authority, that I, the said Thomas William
Sturgeon, my exors, admors, and assigns, should and lawfully might, during
the term of years therein expressed, make, use, exercise, and vend, within
England, Wales, and Town of Berwick-upon-Tweed, my Invention of
"CERTAIN IMPROVEMENTS ON A MICROMETER;" in which said Letters Patent
there is contained a proviso, obliging me, the said Thomas William Sturgeon,
by an instrument in writing under my hand and seal, to cause a particular
description of the nature of my said Invention, and in what manner
the same is to be performed, to be enrolled in His Majesty's High Court
of Chancery within two calendar months after the date of the said recited
Letters Patent, as in and by the same, relation being thereunto had, may more
fully and at large appear.

page_text: NOW KNOW YE, that in compliance with the said proviso, I, the said
Thomas Sturgeon, do hereby declare that the nature of my said Invention,
and the manner in which the same is to be performed, are particularly
described and ascertained as follows (that is to say):-
:-
In the Figures annexed, Fix. 1 denotes a stage or plate, which is fixed at
the inner end or extremity of that part of the tube of a telescope which con-
tains those lens or lenses of the eye piece which are usually placed between
the micrometer and the eye of the observer. i represents a wire, hair, or thread
across the field or view; and the dark lines a, b, and c, d, represent two spiral
grooves cut in the said stage or plate correctly, equal and similar to each other,
and having the radii thereof regularly encreasing in arithmetical progression
as the angular distance of each radius measured from the inner extremity of
the spiral groove to which the said radius belongs, becomes greater. Fig. 2
represents another stage or plate, to be fixed within the eye piece of the
said telescope at the place where cross wires or threads of a micrometer are
usually placed, namely, the focal point or place where the last images of
objects are distinctly seen; and the tube which carries Fig. 1, being inserted
into that which carries Fig. 2, the said stages or plates will be applied face to
face when the instrument is put together. The dark shaded square pieces
p, q, m, n, represent two sliding micrometer pieces, such as may carry move-
able wires; but in preference, I perforate the said pieces at g and h so as
to leave a fine thin part at the inner part of the periphery of each perforation.
e and fare two small studs or pins which become inserted in the spirals
c, d, and a, b, respectively, when the apparatus is put together; and is a
wire, hair, or thread fixed in the aperture of Fig. 2; and the said wire, hair,
or thread is so placed and adjusted in the usual manner by screws that
the same shall pass through the centre of the figure or the axis of vision,
and shall apparently coincide with the wire, hair, or thread i, whenever the
studs or pinse and f shall respectively be situated at either of the extre-
mities of the spirals c, d, and a, b, respectively; and the inner edges of
the pieces p, q, and m, n, are so formed, made, or situated with respect to
the studs or pins e and f, that whensoever the said studs or pins shall
respectively be situated at the inner. extremities of the said spirals, the
said inner edges shall be in contact or apparent contact. And farther,
I do declare that the angular rotation of the said portion of tube carry-
ing the stage or piece, Fig. 1 will cause the studs or pins to slide or move
along within the said spiral grooves, and will produce an approach or recess of
the pieces p, q, and m, n, to or from each other, and will also cause the wire,
hair, or thread i to form an angle with the wire, hair, or thread k, which will be

page_text: measured by the quantity or arc of the said rotation; and consequently, that
while the relative situations of g and h will measure or indicate angles formed
by rays issuing from the extremities of objects, and falling on the centre of the
object lens as usual, the relative positions the lines i and k will measure or
indicate angles upon the plane of the picture in the field of view; and farther,
that I do measure the said angles by a graduation made upon either of the
said tubes, or upon a plate or circle, having its centre in the axis of vision, and
affixed to either of the said tubes; and the divisions of graduation may be
either degrees, in order to enable the observer to read off the situation of the
wire, hair, or thread i more readily, or the same divisions may denote minutes
and seconds, subtended between the micrometer pieces p, q, m, n; or both
the said setts, or any other range of divisions which may be preferred, can
and may be made, used and adopted; and in order that the run or quantity
of the divisions may, if required, correspond precisely with certain numbers of
minutes and seconds, I do in that case produce the final adjustment by a
slight alteration in the position of the amplifying lens, or such other lens of the
microscopic part of the instrument, as opticians well know will alter the size of
the last focal image. And lastly, I do prevent all shake or lost time in running
the said studs or pins backwards and forwards in the said spiral grooves by
applying a suitable spring or springs to the said two micrometer pieces, or
according to the well known methods of applying springs for the like purposes.
In witness whereof, I, the said Thomas William Sturgeon, have here-
unto set my hand and seal, the Twenty-seventh day of May, in the
year of our Lord One thousand eight hundred and eleven.