An Improved Calliper Instrument for Measuring and Calculating Purposes.
Year: 1899

page_text: Date of Application, 16th May, 1899
Complete Specification Left, 16th Mar., 1900-Accepted, 21st Apr., 1900
PROVISIONAL SPECIFICATION.
An Improved Calliper Instrument for Measuring and Calculating
Purposes.
HENRY HANDLEY PRIDHAM POWLES, of 90, Oakley Street, Chelsea, Civil
Engineer, do hereby declare the nature of this invention to be as follows:-
This invention relates to measuring instruments, & is based on the fact that
the versed sine of an angle varies as the square of the chord of the arc subtending
the angle. One form of the instrument used for giving the area of a circle from
the measurement of its diameter consists of a pair of callipers for measuring the
diameter of a circle. Attached to the callipers is a system of levers & guides
arranged so as to move an index, vernier, or scale in the direction of the versed
sine of the angle, whilst the distance between the calliper jaws, measures the chord
of the arc subtending the angle whose versed sine is measured by the index,
vernier, or scale. I have only described one form of this instrument, but it will
be easily seen that it is capable of considerable modification. It is not intended
that the use of the instrument should be confined to the determing of the areas
of circles alone conversly may be used for determing the diameter of circles
of given areas, and also by modification of the scale for determing the areas
of squares when the side is given, or conversley; or for squaring a number and
the converse; extracting the square root.
An Improved Calliper Instrument for Measuring and Calculating
Purposes.
I, HENRY HANDLEY PRIDHAM POWLES, of 90, Oakley Street, Chelsea, 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:-
My invention relates to an improved calliper instrument for measuring and
calculating purposes.
It is a fact well known to mathematicians that the versed sine of an angle
varies as the square of the chord of the arc subtending the angle, and according
to my invention I make use of this fact in constructing an instrument of a calliper
type in which by means of a system of levers and guides an index is caused to
move on a straight scale so that the versed sine of the angle through which the
calliper jaws have been moved is measured by the movement of said index. It

page_text: is clear therefore that if the scale be composed of equal divisions the reading
thereon will be proportional to the square of the distance between the calliper
jaws. Hence by properly calibrating the scale the areas of circles of which the
callipers measure the diameter and the areas of squares of which the callipers
ineasure the side can be read off from the scale. Moreover, since the scale is
equally divided a vernier can be used by which means great accuracy in the
reading can be obtained.
In the accompanying drawings,
Figure 1 is an elevation, of an instrumento constructed according to 'my in-
vention, with the jaws closed, and
Figure 2 is a similar view shewing the jaws open
Figure 3 is a diagram hereinafter explained.
Figure 4,is an elevation shewing a special construction of the calliper jaws, and
Figure 5 is a section on the line VV, Ligure 4.
:
Referring now to Figures 1 and 2, A, B, are the jaws of the callipers, one of
which is secured or forms part of a suitable framework B, and the other of which
is carried on a suitable,bar Apivoted at C to the frame B. Pivoted at a suitable
point to the frame 13 is a straight arm E on which a piece F is fitted to slide.
- Said piece. E has rigidly secured to it an arm G adapted to slide. on the arm A¹
in a direction perpendicular to the direction of movement of the part with
reference to the arm E. The guides for the slides may be arranged in any suitable
manner, the special construction of the parts being immaterial. The arm: A
is provided with a scale A2, and the arm G is provided with a suitable pointer G
which may form the zero-division of avernier G2 where accuracy is.desired.
:
Referring now to Figure 3, c b and e a are radii of a circle with centre c. etis
a, perpendicular from the point b on the line ca, and the distance from point a
to the foot of this perpendicular is the versed sine of the angle b c a... When the
angle beais zero point a coincides with point.b and the versed sine = 0, and
it will be readily understood that the distance through which the foot of the per-
pendicular e moves along the radius ac is proportional to the versed sine of the
angle ul. Comparing now the diagram Figure 3 with Figures 1 and 2, the
point I corresponds to the point and the arm E corresponds to the perpendi-
cular e.
Since the index or pointer G is at a fixed distance from the arm E and
the scale A² is perpendicular to said arm it is clear that the movement of the
pointer. G along the scale is proportional to the versed sine of the angle 'through
which the 'calliper jaws A, B, have been moved. If when the jaws are closed.
that is to say in the position shewn in Figure 1, the index G¹ is made to coincide
with the zero of the scale A2 then the distance along said scale to which the
pointer G has moved when the jaws are opened will be proportional to the versed
sine of the angle through which the jaws-are-moved. The points of the jaws A,
B, are of course at a fixed radial distance from the centre C, consequently the
distance between said jaws is proportional to the chord of the arc subtended by
that angle. It follows, therefore, that the reading on the scale A2 will be pro-
portional to the square of the distance between the jaws A, B. By properly
calibrating the scale A2 the reading thereon may be arranged to indicate the area
of the circle the diameter of which is equal to the distance between .the jaws A, B,
or I can arrange that said reading shall be equal to the area of a square whose
side is equal to the distance between said jaws. Conversely, if the area of a circle
or square be given and the jaws opened so that the index G is opposite the number
on the scale A2 denoting such area the distance between the jaws A, B, will be
the diameter of a circle having said area or the side of a square of the same area.
The instrument can therefore be used for obtaining the squares or square roots
of numbers.
I sometimes provide a circular scale B² on the frame 13¹ which in conjunction
with a pointer or vernier A³ attached to the arm A may be used to indicate the
distance between the jaws A, B.
In order to prevent injury to objects which are placed between the jaws A, B,

page_text: for the purposes of measurement I sometimes construct said jaws in the manner
shewn in Figures 4 and 5, in which two semi-cylindrical pieces H are provided, one
in each jaw, and engaging with the jaws by means of rings H¹ formed at the ends
of said pieces; these rings are shewn in Figure 5 as being V-shaped in cross-
section but other sections may be used. With jaws of this description the plane
faces of the semi-cylinders wili always remain parallel when the jaws are closed
upon any object, and consequently the injury which may result from using jaws
with sharp points may be avoided.
My improved instrument may be employed for various purposes, the scale being
calibrated and marked in accordance with requirements. As an example, the
resistance of a wire to the passage of an electric current being proportional to
the square of its diameter the scale A2 may be marked so as to shew the resis
tance per centimeter length of a wire of given conductivity if its diameter is measured
between the calliper jaws, or the scale may be arranged to denote the number of
amperes of current which a wire can safely carry. I have shewn in Figures 1
and 2 of the drawings a practical embodiment of my invention I wish it under-
stood, however, that I do not confine myself to the precise form illustrated as
various modifications in detail may be made without departing from the scope
of my invention.
Having now particularly described and ascertained the nature of my said in-
vention and in what manner the same is to be performed, I declare that what I
claim is:-
1. A calliper instrument for measuring and calculating purposes having at-
tached to its arms a system of levers and guides so arranged that a point on one
of said levers moves in a straight line through distances proportional to the
versed sine of the angle through which the calliper jaws have been moved.
2. An improved calliper instrument for measuring and calculating purposes,
constructed and operating substantially as described.
111
1000
W. P. THOMPSON & Co.,
322, High Holborn, London, W.C., Patent Agents for the Applicant.”