Improvements in Optical Squares.
Year: 1895

page_text: Improvements in Optical Squares.
I RALPH STANLEY SMITH of Poona, Bombay Presidency, India, Mechanical
Engineer, do hereby declare the nature of this invention to be as follows:―
My said invention relates to optical squares such as used by surveyors, engineers,
and architects for determining a required position at which lines from three
respective points intersect in a horizontal plane to form two right angles.
As is well known the optical square has to a great extent superseded the cross
staff owing to the greater facility in handling the former. To make use of the
optical square some preparatory arrangement must however be made to define the
base line between two stations upon which the operator is to work before he can
determine with any degree of accuracy his position on that line with regard to any
given off set, since with the optical square it is only possible to consider one right
angle at a time.
My invention consists of a series of four mirrors arranged in such a manner that
by its use the operator when stationed at a point say a can see three other points
say pos which form with a two right augles. Conversely it enables him to find
the point if the three other points are given.
'
My invention thus adapts itself to the simultaneous consideration of three
individual and necessary points of which only two would otherwise be observed at
a tiine.
It consists essentially of four mirrors say a, b, c, and d, mounted in a suitable
case or frame a and b being in proximity and forming as seen in plan a right angle
whose hypotenuse is parallel with the front edge of the instrument. The mirror c
mounted at the same end is set at right angles with the front edge. At the other
end of the instrument and directly before the sight hole is fixed another mirror d
forming an angle of 45 degrees with the front edge of the instrument. The
height of the mirior b is twice that of a, and the height of cis three times that
of a. The height of the mirror d is just sufficient to conveniently reflect the three
visible parts of the mirrors a, b, and c, without obstructing the line of vision.
The rays of light entering at the front back and one end of the instrument are
reflected by the mirrors to the sight hole. The operator when standing at the
supposed point x, and facing the points will see the point p behind him, o to the
left, and s in front of him. When three such objects coincide in a vertical line on
the mirror opposite the sight hole the observer is at that point on a line from p
towards & upon which the line or falls so as to form two right angles with it.
In use the observer having found the position in which the reflections of the
three objects coincide would then tuin on his heel in the direction of the offset and
see whether it coincides again with the point that was previously behind.
so the instrument. is in good adjustment.
In some forms of my said invention I substitute prisms for mirrors.
TTON.
If it is

page_text: Improvements in Optical Squares.
I RALPH STANLEY SMITH of Poona, Bombay Presidency, India, Mechanical
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 :-
My said invention relates to optical squares such as used by surveyors, engineers,
and architects for determining a required position at which lines from three
respective points intersect in a horizontal plane to form two right angles.
As is well known the optical square has to a great extent superseded the cross
staff owing to the greater facility in handling the former. To make use of the
optical square some preparatory arrangement must however be made to define the
base line between two stations upon which the operator is to work before he cau
determine with any degree of accuracy his position on that line with regard to any
given off set, since with the optical square it is only possible to consider one right
angle at a time.
In order to clearly set forth my said invention I will describe it with reference
to the accompanying drawings, in which
Fig. 1 is a diagram showing in plan the points to be observed.
Fig. 2 is a sectional plan of an instrument made in accordance with my said
invention.
Fig. 3 is a side elevation of the mirrors (the sectional parts represent the mirror
glass).
Fig. 4 a perspective view of the interior of the frame.
Fig. 5 an end view.
Fig. 6 an external perspective view of the entire instrument.
My said invention consists of a series of mirrors arranged in such a manner that
the user when stationed at a point say of Fig. 1 can see three other points
sayos which form with a two right angles. Conversely it enables him to find
the point if the three other points are given.
My invention thus adapts itself to the simultaneous consideration of three
individual and necessary points of which only two would otherwise be observed at
a time.
It consists essentially of four mirrors say a, b, c, and d, (Fig. 2) mounted in a
suitable case or frame. The mirrors a and b are in proximity and form as seen in
plan a right angle whose hypotenuse is parallel with the front edge of the
instrument. The mirror c mounted at the same end stands at right angles to the
front edge. At the other end of the instrument say about four and a half inches
from and directly before the sight hole is the mirror d forming an angle of
45 degrees with the front edge of the instrument. The height of the mirror bis
twice that of a, and the height of c is three times that of a. The height of the
mirror d is just sufficient to conveniently reflect the three visible parts of the
mirrors a, b, and c, without obstructing the line of vision.
The rays of light represented by arrows entering at ef and g are reflected by
the mirrors to the sight hole h. The operator when standing at the supposed
point, and facing the points will see the point p behind him, o to the left, and s
in front of him. When three such objects coincide in a vertical line on the
mirror d opposite the sight hole the observer is at that point on a line from p
towards & upon which the line o a falls so as to form two right angles with it.
In use the observer having found the position in which the reflections of the
three objects coincide would then turn on his heel in the direction of the offset and
see whether it coincides again with the point that was previously behind. If it is
so the instrument is in good adjustment.

page_text: Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is.―
The combination in an optical square of four mirrors substantially as set forth
and described
E. T. WHITELOW, A.M. Inst. C.E.,
70 Deansgate, Manchester, Agent for the Applicant.