IMPROVEMENTS IN REPLECTING OPTICAL INSTRUMENTS."
Year: 1866

page_text: LETTERS PATENT to Henry Temple Humphreys, of 28, Westbourne Park
Road, in tho County of Middlesex, Civil Engineer, for the Invention of
"IMPROVEMENTS IN REPLECTING OPTICAL INSTRUMENTS."
PROVISIONAL SPECIFICATION left by the said Henry Temple Humphreys
at the Office of the Commissioners of Patents, with his Petition, on the
9th March 1866..
I, HENRY TEMPLE HUMPHREYS, of 28, Westbourne Park Road, in the
County of Middlesex, Civil Engineer, do hereby declare the nature of the
said Invention for "IMPROVEMENTS IN REPLECTING OPTICAL INSTRUMENTS," to be
as follows:-
Firstly, for the principles and constructions of instruments for the setting
out of railway and other curves in the field and on public or private works.
generally, and intended to supersede the use of the theodelite for those pur-
poses; secondly, for the same principles and constructions of instruments
applied to setting out curves of large radius on paper; thirdly, for the same
principles and constructions of instruments applied to the measurements of
angles and altitudes, and for most of the purposes for which the sextant and
theodolite are at present employed; fourthly, for the same principles and
constructions of instruments applied to measuring distances for civil, military,
and maritime purposes; fifthly, for the same principles and constructions of
instruments applied as a goniometer to measure the angles of crystals, which

page_text: application depends on the apparent radial positions of the successive reflected
images as seen from a fixed point. For these above-named purposes I pro-
pose to make an instrument in the form of a short cylinder of a length about
equal to its diameter, with plane mirrors placed at each end of the said
cylinder; one of these mirrors is fixed perpendicular to the cylindrical axis,
and is silvered over its whole area, the other is silvered over half its area
only, and is arranged to move angularly on an axis perpendicular to the
cylindrical axis. Suitable arrangements are constructed whereby the angle
subtended between the fixed and the moveable mirrors may be very readily
altered at will to any angular magnitude required, by which means a series of
reflections of any object looked at through a small hole in the fixed mirror
will appear in the half mirror ranged at regular intervals, and will fall upon
the circumference of a mathematically true circle, whose radius is thus
mathematically determinable, This effect depends upon a well-known theorem
in mathematical optics, and is described in all treatises on the subject as com-
bined or successive reflections. The curve is set out by planting poles or
pins at uniform distances in the line of direct vision with the images seen in
the half mirror.
Generally I claim the principles conveyed by the above Invention in their
applications as previously stated; generally also the use of any part or the
whole of the above separately or combined with any other instrument, or with
a telescope or a microscope added binocularly or otherwise, either in the form
as above specified, or in the box-sextant shape, with a graduated limb and
vernier to set the mirrors, or in a square form with tangential screw move-
ment, or any other form or shape or application involving the principle of
successive reflections between two plane mirrors applied to an optical
instrument,
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Henry Temple Humphreys in the Great Seal Patent Office
on the 8th September 1866.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HENRY
TEMPLE HUMPHREYS, of 28, Westbourne Park Road, in the County of Mid-
dlesex, Civil Engineer, send greeting.
3
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Ninth day of March, in the year of our Lord 3
One thousand eight hundred and sixty-six, in the twenty-ninth year of IIer

page_text: reign, did, for. Herself, Her heirs and successors, give and grant unto me, the
said Henry Temple Humphreys, Her special licence that I, the said Henry
Temple Humphreys, my executors, administrators, and assigns, or such others
as I, the said Henry Temple Humphreys, my executors, administrators, 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 Kingdom of Great
Britain and Ireland, the Channel Islands, and Isle of Man, an Invention
for "IMPROVEMENTS: IN REFLECTING OPTICAL INSTRUMENTS," upon the condition
(amongst others) that I, the said Henry Temple Humphreys, my executors
or administrators, by an instrument in writing under my, or their, or one 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 tho 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 Henry Temple Humphroys, do hereby
declaro 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: :
Firstly, for the principles and constructions of instruments for the setting
out of railway and other curves in the field and on public or private works
generally, and intended to supersede the use of the theodolite for those pur-
poses; secondly, for the same principles and constructions of instruments applied
to setting out curves of large radius on paper; thirdly, for the same principles
and constructions of instruments applied to the measurements of angles and
altitudes, and for most of the purposes for which the sextant and theodolite
are at present employed; fourthly, for the same principles and constructions of
instruments applied to measuring distances for civil, military, and maritime
purposes; fifthly, for the same principles and constructions of instruments
applied as a goniometer to measure tho angles of crystals. The principle upon
which all these applications depend is that of combined or successive reflections
between two plane mirrors, which is a well-known theorem in mathematical
optics, and is fully described in most treatises on the subject.
The accompanying Diagram illustrative of the optical principles of the
instrument shows how the combined or successive reflections of any object
form images around the circumference of a mathematically true circle at
apparent angular distances all equal to one another, but it must be observed
that the radius of the curve of the images shown in the Diagram bears no
relation whatever to that of any curve which it is desired to set out, other than

page_text: it is created by a series of tangential angles, for by simply altering the length
of chain with which the curve is staked out the radius of the curvo is corro-
spondingly altered in a direct ratio. For these above-named purposes I pro-
pose to make an instrument in the form of a short cylinder of a length about
equal to its diameter, with plane mirrors placed at each end of the said.
cylinder; one of these mirrors is fixed perpendicular to the cylindrical axis,
and is silvered over its whole area, the other is silvered over half its area only,
and is arranged to move angularly on an axis perpendicular to the cylindrical
axis. Suitable arrangements are constructed whereby the angle subtended
between the fixed and the moveable mirrors may be very readily altered at will
to any angular magnitude required, by which means a series of reflections of any
object looked at through a small holo in the fixed mirror will appear in the
half mirror ranged at regular intervals, and will fall upon the circumference
of a mathematically true circle, whose radius is thus mathematically deter-
minable. The curve is set out by planting poles or pins at uniform distances
in the line of direct vision with the images seen in the half mirror.
Generally I claim the principles conveyed by the above Invention in their
applications as previously stated; generally also the use of any part or the
whole of the above separately or combined with any other instrument, or with
a telescope or a microscope added binocularly or otherwise, either in the form
as above specified, or in the box-sextant shape with a graduated limb and
vernier to set the mirrors, or in a square form with tangential screw move-
ment, or any other form or shape or application involving the principle of
successive reflections between two plane mirrors placed opposite or nearly so
to the eye, and applied to an optical instrument.
In witness whereof, I, the said Henry Temple Humphreys, have hereunto
set hand and seal, this Seventh day of September, in the year of our
Lord One thousand eight hundred and sixty-six.
HENRY TEMPLE HUMPHREYS. (L.S.)