CERTAIN IMPROVEMENTS IN MATHEMATICAL INSTRUMENTS
Year: 1812

page_text: SCHMALCALDER'S SPECIFICATION.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, CHARLES
AUGUSTUS SCHMALCALDER, of the Strand, in the City of Westminster, and
County of Middlesex, Mathematical Instrument Maker, 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 Fifth day of March,
in the fifty-second year of His reign, give and grant unto me, the said
Charles Augustus Schmalcalder, my exors, adñiors, and assigns, His especial
licence, full power, sole privilege and authority, that I, the said Charles
Augustus Schmalcalder, my exors, admors, and assigns, should and lawfully
might, during the term of years therein mentioned, make, use, exercise,
and vend, within England, Wales, and Town of Berwick-upon-Tweed, my In-
vention of "CERTAIN IMPROVEMENTS IN MATHEMATICAL INSTRUMENTS;" in which
said Letters Patent there is contained a proviso that if I, the said Charles
Augustus Schmalcalder, shall not particularly describe and ascertain the nature
of my said Invention, and the manner in which the same is to be performed,
by an instrument in writing under my hand and seal, and cause the same to
be enrolled in His Majesty's High Court of Chancery within two calendar
months next and immediately after the date of the said Letters Patent, that
then the said Letters Patent, and all liberties and advantages whatsoever

page_text: thereby granted, shall utterly cease, determine, and become void, as in and by
the same (relation being thereunto had) may more fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
Charles Augustus Schmalcalder, do hereby declare that the nature of my said
Invention, and the manner in which the same is to be performed, are described
and ascertained as follows (that is to say) :-
-
In the first place I do adapt and apply to mariners' compasses, theodolites,
and other instruments for measuring angles of azimuth or bearing, a three-
sided prism having two plain surfaces, forming an angle of forty-five degrees,
or nearly that quantity, with each other, and having the third surface ground
spherically convex, in such a manner as that a line drawn perpendicular to the
line of intersection of the said plane surfaces, and through the middle point of
one of the said surfaces, shall not be far distant from the plane of a great
circle of the said spherical convexity lying parallel to the said plane
surface; or, in other words, that the optical axis of the said spherical surface,
parallel to and within one of the said plane surfaces, shall not far distance
from that surface. And I do so adopt and apply the said prism that the
convex surface shall face the divisions of the compass card or theodolite
limb, or other equivalent part of the said other instrument, and the plane
surface nearest and parallel to the said axis of the spherical surface shall be
opposite the eye of the observer. And in these circumstances the other plane
surface will be so inclined as to shew the said divisions by reflexion, and render
it practicable at the same time for the observer to see by direct vision the
subject of observation by bringing for that purpose part of the pupil of the eye
above the angular edge of the prism; and in this manner the line of collima-
tion will become the index to the said divisions, and the azimuth or bearing
may be taken and read off at one observation.
Secondly, I do make the like adaptation and application, mutatis mutandis,
to instruments for measuring vertical or oblique angles, and also to the spirit
level of the levelling instrument.
Thirdly, I do make a four-sided pyramid having a square base, and two of
the sides of the said pyramid are at right angles to the base and to each
other, and the other two sides are so inclined to the base that each of them
makes an angle therewith of forty-five degrees or thereabouts; and in case
the eye be placed against the base of the said pyramid the observer will see an
object or objects reflected by each of the inclined sides at the same time; and
I do place one of the first-mentioned sides above or against the horizontal
divisions of the compass card or theodolite limb, or other instrument, so that
those divisions can be read off in a similar manner to that already described

page_text: by the prismatic lens first mentioned; and I do place the other of those two
first-mentioned sides opposite to a plumb line, spherit level, or the divisions of
a theodolite or other instrument, so that at the same time that the subject
of observation is seen by direct vision or otherwise, the station or position of
such plumb line, or the bubble. of such spirit level, or divisions of other instru-
ments, is seen by means of one reflecting or inclined surface, while the divisions
are seen and read off by means of the other reflecting or inclined surface; and
in cases where a magnifying power is required I do make the two first-
mentioned sides, which are at right angles with the base of the said pyramid,
spherically convex, so that the divisions to be read off may opposite to or
nearly in the focus of one spherical side, and the plumb line, or bubble of the
spirit level, or divisions of a theodolite or other instrument, may be opposite to
or nearly in the focus of the other spherical side.
Fourthly, I do apply the said prismatic reflectors, not only in their simple
state, but also to the telescope of instruments for observation, such as quad-
rants, Hadley's sextants, and the like, and do by that means find the angles of
azimuth and altitude without requiring two or three observers to operate
together, as is commonly practised.
And I do farther declare, that in such instruments as do not require a
magnifying power in the said prismatic or compound reflectors I do not make
any of the surfaces convex, but do substitute or make a plane surface or
surfaces, and at right angles to that plane which is intended to be opposite
the eye of the observer.
And the Drawings in the margin hereof, in the illustration of the premises,
do represent, Figs. 1, 2, and 3; a compass improved in the manner herein-
before described, wherein a is the line of collimation or sight, against or upon
which the divisions of c, the card, are scen, magnified by b, the reflecting
prism. In Fig. 1 the same is turned back to allow the cover to be put on after
shutting down the sight a.
Fig. 4 and 5 shews the manner of attaching the compass, or any other
instrument for giving azimuths or altitudes, along with my said improvements,
to the eye-end of the tellescope. By attaching a sextant to the object-end of
the same tellescope I take the altitude and azimuth at the same time.
In witness whereof, I, the said Charles Augustus Schmalcalder, have
hereunto set my hand and seal, the Second day of May, in the year
of our Lord One thousand eight hundred and twelve.
C. A. SCHMALCALDER. (L.S.)

page_text: AND BE IT REMEMBERED, that on the Second day of May, in the year
of our Lord 1812, the aforesaid Charles Augustus Schmalcalder came before our
said Lord the King in His Chancery, and acknowledged the Specification
aforesaid, and all and every thing therein contained and specified, in form
above written. And also the Specification aforesaid was stampt according
to the tenor of the Statute made for that purpose.
Inrolled the Second day of May, in the year of our Lord One thousand
eight hundred and twelve.