Improvements in Hand Levels.
Year: 1895

page_text: Improvements in Hand Levels.
I RALPH STANLEY SMITH of Poona, Bombay Presidency, India, Mechanical
Engineer, do hereby declare the nature of this invention to be as follows:-
The invention consists of an instrument for obtaining observations level with the
eye of the observer without the preparatory adjustment of any part of it. When
held in the hand it maintains its steadiness of action in spite of any slight move-
ment of the hand that holds it or the tilting of the instrument itself.
The instrument consists essentially of an arched spirit-level two mirrors and an
eve piece.
The two mirrors are placed at a small distance apart and form on their inner
reflecting sides an angle of 45 degrees.
The arched spirit-level is fixed evenly above one of the mirrors with the middle
radius of its arc passing vertically through the centre of the mirror.
The eye piece is fixed opposite the second mirror and at such a distance from it
that the distance from the eye piece to the second mirror and thence to the first
mirror shall be equal to the radius of the arched level less the distance of the first
mirror from the level. Thus the whole line of reflection from the eye piece to the
are is made equal to the radius of the arc. The reflection of the arc seen from the
eye piece is therefore similar to the actual arc as seen from its centre of curvature
with the difference that it will be seen horizontally.
The air bubble will always maintain a vertical position above the centre of
curvature of the level however the instrument may be tilted within the limits of
range of the level itself. And in the apparent level seen from the eye piece the
reflection of the air bubble will always maintain a position horizontal with the eye
piece within the before mentioned limits.
The reflected arc will lie at exactly the same radius from the eye piece as the
real arc does from the actual centre of curvature and the divergence of the bubble
consequent upon moving the instrument meets with a corresponding divergence in
the reflected level, which divergence is caused to assume not only the same degree
but the same direction as well.
In the complete instrument a small adjustment of the angle of the first mirror
may be made so that one of the ends of the bubble may be brought into the line of
sight and thus a more definite horizon may be presented than the centre of the
bubble would offer.
A partially silvered mirror should be used for the fore horizon glass in order to
render a definite edge to the bubble.
Dated this 28th day of August 1895
E. T. WHITELOW, A.M. Inst. C.E.,
70 Deansgate, Manchester, Agent for the Applicant.

page_text: 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 :--
The invention consists of an instrument for obtaining observations level with the
eye of the observer without the preparatory adjustment of any part of it.
When
beld in the hand it maintains its steadiness of action in spite of any slight move-
ment of the hand that holds it or the tilting of the instrument itself."
In order to more fully set forth my said invention I will describe it with
reference to the accompanying drawing.
The instrument consists essentially of an arched spirit-level s two mirrors a and b .
and an eye piece placed at e.
The two mirrors a and b are placed at a small distance apart and form on their
inner reflecting sides an angle of 45 degrees.
The arched spirit-levels is fixed evenly above one of the mirrors & with the
middle radius os of its arc passing vertically through the centre of the mirror.
Referring first to Fig. 1 the eye piece e is fixed opposite the centre of the other
mirror a and at such a distance from it that the distance e a + a b shall be equal
to o b. Thus the whole line of reflection ea+ab+bs from the eye piece to the
arc is made equal to the radius of the arc. The reflection of the arc seen from the
eye piece is therefore similar to the actual arc as seen from its centre of curvature o
with the difference that it will be seen horizontally.
As o is the centre of a circle of which the levels is an arc the air bubble will
always maintain a vertical position above the centre of curvature o of the level
however the instrument may be tilted within the limits of range of the level itself,
and in the apparent level seen from the eye piece the reflection of the air bubble
will always maintain a position horizontal with the eye piece within the before
mentioned limits.
Referring to Fig. 2 it will be seen that bs is common to the radius of the
reflected arc and the radius of the actual arc it matters not therefore at what
distance above b the are is described so long as it is described from the same centre
i.e. so long as the part of its radius below b is equal in length to the remainder of
the line of reflection from e.
The reflected arc will lie at exactly the same radius from the eye piece e as the
real arc does from the actual centre of curvature and the divergence of the bubble
consequent upon moving the instrument meets with a corresponding divergence in
the reflected level, which divergence is caused to assume not only the same degree
but the same direction as well.
In the complete instrument provision may be made for a small adjustment of the
angle of the first mirror so that one of the ends of the bubble may be brought into
the line of sight and thus a more definite horizon may be presented than the centre
of the bubble would offer.
A partially silvered mirror should be used for the fore horizon glass in order to
render a definite edge to the bubble as shown in Fig. 3.
The mirrors level and eye piece may be mounted in any suitable framework or
holder as will be well understood without further description.

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 of a curved spirit levels and the mirrors a and b substantially
as and for the purpose set forth and shown.
Dated this 27th day of May 1896.
E. T. WHITELOW, A.M. Inst. C.E.,
70 Deansgate, Manchester, Agent for the Applicant.