Year: 1888

page_text: Date of Application, 13th July, 1888
Complete Specification Left, 6th Apr., 1889
Complete Specification Accepted, 8th June. 1889
PATRICK JOHN LYNAM, Civil Engineer, of Woodlawn, Mount Pleasant, County
Louth do hereby declare the nature of this invention to be as follows:-
This invention applies to that class of Range Finders in which two angular
instruments are used, one at each end of a base line, one instrument measuring a
constant angle, the second instrument being graduated to read the ranges; and
consists in the use (in the second instrument above described) of a reflector, with the
necessary diminishing or magnifying power, so placed that when the sights are
adjusted to find a range, the range can be seen on a graduated disc by reflection and
read off direct without any movement of the eye. For example I prefer to use a
magnifying and totally reflecting prism placed at the rear sight as in an ordinary
Prismatic Compass, the compass card of the Prismatic Compass being replaced by a
disc graduated to read the ranges and rotated by the movement of the sights.

page_text: 1, PATRICK JOHN LYNAM, of Woodlawn, Mount Pleasant, County Louth, Civil
Engineer do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement :-
This Invention has reference to that class of Range Finders which consist of two
angular Instruments (or Instruments for measuring angles) connected by a Base Line
of constant length, one angular Instrument being constructed to measure a constant
angle and the second angular Instrument being graduated to read Ranges. The
Invention consists in providing the second or graduated angular Instrument with a
Reflector, having the necessary diminishing or magnifying power, so placed that the
graduations can be seen and read off from the Eye hole or Eye glass of the Instrument,
so that the Observer having set the Instrument to take a Range can see the graduations
by reflection and read them off with little or no movement of his Eye and without
disturbing the position of the Instrument.
The angular Instruments are most conveniently constructed on the principle of the
Sextant, that is, each Instrument is to be constructed with two Mirrors so placed that
an Observer on looking through the Instrument can see one object direct and another
object by double reflection from the two Mirrors in succession. Each Instrument
measures the angle subtended at itself by the other Instrument and the Distant Object
whose Range is to be found. One Instrument has fixed Mirrors so as always to
measure the same angle. The second Instrument (hereinafter referred to as the Range
Finder) has one Mirror fixed but the other Mirror is placed on an Index arm which is
moveable round a pivot as in an ordinary Sextant, but the movement of the Index
arm being very slight it should be connected by suitable gearing with a Dial or Scale
or Druin (hereinafter referred to as the Dial) in such a manner that a very slight
angular movement of the Mirror gives a much larger and more easily estimated
movement of the Dial. This Invention has reference only to a mode in which the
Observer who uses the Range Finder, after he has set the Instrument to read a Range,
can read off the Range on the Dial without disturbing the position of the Instrument
and without materially disturbing the position of his own Eye.
The annexed Drawings shew two methods of applying the Invention. Figure 1 is
a vertical section shewing a portion of a Range Finder constructed without telescopes.
A. A is the case of the Instrument, B is the Dial which is graduated round its periphery
on its upper surface. The Dial B turns on a vertical axis shewn at B, and is to be
connected by any suitable gearing with the moveable Mirror in such a manner that
when the Mirror is set to measure any angle the Index Point (which is fixed to the
case A) points to the corresponding Range on the Dial B. The Mirrors and gearing

page_text: not being material to the Invention are not shewn on the Drawings. D is a magni-
fying and totally reflecting Prism of glass, enclosed in a brass casing E. The brass
casing E extends above the Prism and has a slot cut in it as shewn at F exposing a
part of the glass Prism, it also has an opening below as shewn at G so that an
Observer who places his Eye at F can see in the Prism D a magnified image of the
Index Point C and of the graduations on the Dial B near C. The Prism D and its
casing E are made so as to be moveable up and down to obtain distinct vision of the
graduations on the Dial, and the Dial may be made moveable up and down with the
same object.
The Mode of Operation is as follows: The Observer looks through the upper
portion of the slot in the direction of the dotted line H and sets the Instrument to
take a Range, operating the gearing so as to alter the position of the moveable Mirror
and at the same time to turn the Dial B through a corresponding angle, he then
lowers the position of his Eye slightly (or raises the Irism D slightly) and looking
through the Prism in the direction of the dotted line K reads off the Range on the
Dial Bat the Index Point C. The Observer then raises his Eye slightly (or lowers
the Prism slightly) and is then ready to set the Instrument to take another Range.
This Discription applies to the Mode of Operation of the Invention in the Range
Finder Proper, the other Observer with the other Instrument must of course be in
position in the usual manner before a Range can be taken.
Figure 2 is a vertical section shewing a Mode of application of the Invention to a
Range Finder constructed with a telescope. A is the casing, B the Object glass and
C the Eye glass of the telescope. D is the Dial turning about an axis D, placed on
one side of, or below, the case A graduated round its surface and connected by gearing
with the moveable Mirror of the Instrument so that when the Mirror is set to measure
any angle the Index Point E points to the corresponding Range on the Dial D. Fis
a Reflector, that is, a Mirror or a totally reflecting Prism, placed in a recess A, in the
case A and fixed on a rod H. The rod H passes loosely through the case A and
terminates in a button K so that on pressing the button K the Reflector F is depressed
into the position shewn by dotted lines at L. When not in use the Reflector is drawn
into the recess A, by the spring G so as not to interfere with the use of the telescope.
When the Reflector is pressed into the position L the Observer looking through the
Eye-glass C should see in the Reflector a distinct image of the Index Point E and of
the graduations on the Dial D near the Index Point, and to secure this distinct image
the Reflector may be made concave or convex to magnify or diminish the image, or
the Reflector may be a Prism giving a magnified or diminished image, or an additional
lens may be introduced as shewn at M to magnify or diminish the image. If the
telescope be constructed on Galileo's principle the Eye glass C will be concave giving
a diminished image and the Reflector F and lens M must generally be made to
magnify the image. If the telescope he constructed on the principle of the
Astronomical telescope the Eye glass C will give a magnified image and the Reflector F
may generally be made to give an unaltered or diminished image.
The Mode of Operation of this arrangement is as follows: The Instrument having
been set to take a Range (as described for the first arrangement) the Observer presses
the button K so as to depress the Reflector F to the position L and reads off the Range
which he sees on the Dial D at the Index Point E as reflected in the Reflector at L.
The Observer then releases the button K, the Reflector is drawn back to the position F
by the spring G and the Instrument is ready to take another Range.
Having now particularly described and ascertained the nature of my said Inven
ion, and in what manner the same is to be performed, 1 declare that what I
laim is:
First. In Range Finders consisting of a Base Line of constant length, an angular
nstrument to measure a constant angle, and a second angular Instrument graduated
o shew Ranges, the use, in the second or graduated angular Instrument, of a Reflector
with diminishing or magnifying power if necessary for distinct vision) so placed that
he graduations can be seen from the Eye-hole or Eye-glass of the Instrument and so

page_text: arranged that an Observer, having set the Instrument to take a Range, can read the
graduations without altering the position of the Instrument and without materially
altering the position of his own Eye.
Second. In Range Finders as above described, provided with telescopes, the use, in
the second or graduated angular Instrument, of a moveable Reflector which can be
interposed at will between the Eye-glass and the Object-glass of the telescope in such
a manner that the Instrument having been set to take a Range the Observer can move
the Reflector so as to read the graduations through the Eye-glass of the telescope
without disturbing the position of the Instrument or the position of his own Eye.
Dated this Fifth day of April 1889.
PATRICK JOHN LYNAM.