Improvements in Planimeters.
Year: 1891

page_text: Date of Application, 9th Jan., 1891
Complete Specification Left, 3rd Sept., 1891-Accepted, 3rd Oct., 1891
PROVISIONAL SPECIFICATION...
Improvements in Planimeters.
1
I JOHN GOODMAN of the Yorkshire College of the Victoria University, Leeds
in the County of York, Professor of Civil and Mechanical Engineering, do hereby
declare the nature of this invention to be as follows :-
My invention refers to improvements in that description of instrument known as
the "stang" planimeter, which consists essentially of a rod or beam (hereinafter
referred to as the beam) carrying at the one end a pointer or tracer and at the
opposite end a marker or hatchet, hereinafter referred to as the tracer and hatchet
respectively.
The mode of using the "stang" planimeter is as follows:-The tracer is placed
as near as can be judged at the centre of gravity of the figure, whose area is to be
measured, and a dent or impression is made upon the surface of the paper with the
hatchet. The tracer is then moved in a straight line to any point on the boundary
line of the figure and carried completely round and along the boundary line until
reaching the starting point on the boundary line, and therefrom back to the centre
starting point along the previously mentioned straight line. A second dent is then
made with the hatchet. The area of the figure is a function of the distance'
between the two dents and the length of the beam; or more strictly speaking of
the length of the beam and the angle included between the first and final positions
of the beam.
Should the starting point not be in the centre of gravity of the figure, the beam
should be moved round through 180 degrees and the operation as above described
repeated. The mean of the two measurements obtained is to be taken as the
correct distance (between the dents).
Under the expression, "the distance between the dents" is to be understood the
circular or are distance.
If the length of the beam be made adjustable, and in each case be adjusted so as
to be equal to the length of the figure (measured parallel to the direction of the
beam) whose area is to be obtained, then the distance between the hatchet dents
(measured on the arc), gives the mean height of the figure.
Now my invention or improvement consists in making the position of either, or
of both, the tracer and the hatchet adjustable on the beam, so that the distance.
between the same may be varied. To facilitate adjusting the distance between the
tracer and the hatchet I provide indexes, or pointers attached to or forming part,
of the tracer and hatchet respectively, the distance between which is exactly the
same as between the tracer and the hatchet. Or the edges (preferably the inner
ones) of the tracer and hatchet legs may be formed, so as to give exactly the
distance between the tracer and the hatchet. Such edges are formed at right.
angles to the beam.
I have also discovered that if the hatchet be set at an angle with the plane of
the instrument, instead of being exactly in line with it, then the reading obtained
with the instrument is altered, and that such alteration is a function of the angle
by which the hatchet is set askew. When the tracer is carried round the figure in
one direction, the effect is to increase or multiply the reading, but if carried round,
in the opposite direction, the effect is to diminish the reading. Now I purpose as
a further improvement, to construct the instrument with the hatchet purposely set
askew with the plane of the beam, thereby obtaining an increased or magnified
reading, and rendering the instrument more accurate in use.
To obtain points as marks given by the hatchet, I propose in some cases to
provide the hatchet with a pricker, kept raised by means of a spring above the
:

page_text: surface of the paper during manipulation of the instrument, but which can at
pleasure be pressed down so as to make a point mark on the surface of the paper to
facilitate and render more accurate the reading.
My improved apparatus may be made of any suitable material or materials and
of any convenient size. It is specially applicable for obtaining the indicated
horse-power or the average steam pressure from steam or other engine diagrams,
but it may (when suitable scales are provided) be used for all purposes for which
planimeters are now employed.
Dated this 8th day of January 1891.
J. CLARK JEFFERSON,
2, East Parade, Leeds, Agent for Applicant.
COMPLETE SPECIFICATION.
Improvements in Planimeters.
I JOHN GOODMAN of the Yorkshire College of the Victoria University Leeds
in the County of York Professor of Civil and Mechanical Engineering do hereby
declare the nature of this invention and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement :-
My invention refers to improvements in that description of instrument known as
the "stang" planimeter; which consists essentially of a light rod or beam, herein-
after referred to as the beam, carrying at the one end a pointer or tracer and at the
opposite end a marker or hatchet, which are hereinafter referred to as the tracer
and hatchet respectively.
The mode of using the stang planimeter is as follows:-The tracer is placed as
near as can be judged at the centre of the figure, whose area is to be measured, and
a dent or impression is made upon the surface of the paper with the hatchet. The
tracer is then moved away from the instrument side of the figure in a straight line
to a point on the boundary line of the figure, and carried completely round and
along the boundary line until reaching the starting point in the boundary line, and
therefrom back to the centre starting point along the previously mentioned straight
line. A second dent is then made with the hatchet. The area of the figure is a
function of the distance between the two dents and the length of the beam; or
more strictly speaking of the length of the beam and the angle included between
the first and final positions of the beam.
Should the starting point not be in the centre of the figure, the beam should be
moved through 180 degrees and the operation as above described repeated. The
mean of the two measurements thus obtained is to be taken as the correct distance
between the two dents.
Under the expression "the distance between the dents" is to be understood the
circular or arc distance.
If the figure whose area is to be measured is enclosed in a rectangle, and the
length of the beam be made equal to the length of the rectangle, then the distance
between the hatchet dents (measured on the arc), gives the mean height of the
figure.
Now my invention consists in making either the tracer or the hatchet adjustable
on the beam, or both may be made adjustable; or the length of the beam may be
made adjustable by forming it in two parts, the one capable of sliding telescopically
over the other, and of which the one carries the tracer and the other the hatchet.
To facilitate adjusting the distance between the tracer and the hatchet, I provide
indexes or pointers attached to or forming part of the tracer and hatchet respec-
tively; the distance between which is exactly the same as between the tracer and
hatchet. Or the edges (preferably the inner ones) of the tracer and hatchet legs
may be formed, so as to give exactly the distance between the tracer and hatchet.
Such edges are formed at right angles to the beam.

page_text: c is the hatchet leg socket.
d is a small lever hinged to the upper side of the hatchet socket c, the short arm
of which is kept pressed against the beam by means of the spring e under the
longer arm, sufficient friction being thereby obtained to prevent the socket being
unintentionally or inadvertently moved from the position to which it has been
adjusted. By pressing down the longer arm of the lever d however, the hatchet
can be readily shifted in position on the beam.
f is the tracer, which may be permanently fixed to the beam as shewn in the
drawings, or it may be attached thereto by an adjustable socket in a similar manner
to that shewn for the hatchet.
g is the tracer handle, provided at one end with the swivelled conical socket h.
The legs of the hatchet and tracer are shewn half cut away on their sides facing
each other, as and for the purpose previously specified.
As an illustration of the mode of using my improved planimeter, I will describe
its application to ascertaining the mean or average pressure from a steam engine
diagram. Suppose in Fig. 4 ghijkg to represent such a diagram, and a b c d be
the enclosing rectangle, the sides of which are drawn respectively parallel to and
at right angles to the atmospheric line of the diagram. The planimeter is laid on
its side over the figure, and the distance between the hatchet and tracer adjusted
to the length of the figure, by making the inner flat faces to coincide with the
sides be and a d respectively. The point e is then chosen as approximately as can
be guessed at the centre of the diagram, and the point of the tracer placed upon
the point e. Suppose e f to represent the centre line of the beam. A. dent is then
made on the paper at the point f by pressing down the hatchet. The tracer point
is then drawn back from the point e along the prolongation of the line fe to the
point y on the boundary line of the diagram, and the tracer is then carried round
the diagram ya h i j k (in either direction) back to g, and from thence back to the

page_text: starting point e. Suppose e m to be the final position of the beam. A second dent
is then made with the hatchet in its final position (i.e. at m). The distance between
f and m is the average height or pressure given by the diagram. Strictly speaking
the distance fm should be measured on the arc fm, e being the centre. For most
purposes the straight distance or chord fm will be found sufficiently accurate. To
obtain a still more accurate result, the beam should be turned through 180 degrees
round e, and the manipulation repeated; in which case, suppose n and p to be
the starting and final dents of the hatchet respectively, then the mean of the two
readings fm aud n p gives more accurately the height of the figure, in the present
average case the steam pressure.
propose
To facilitate the more accurate reading of the distance between fand
m, I
to furnish the hatchet with a needle pricker as illustrated in Figs. 5 and 6. x is
the needle pinned into the handle y, and passing through a hole or guide in the
foot of the hatchet. A flat spring keeps the handle y and therefore the pricker
needle raised during the manipulation of the instrument. The handle y
pivotted or hinged to the leg. When the beam is in its first and final positions,
a puncture is made with the needle, instead of making a dent with the hatchet,
and the distance between the points thus marked is read as the distance fm.
is
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what I
claim is :-
10. A planimeter consisting of a beam and so-called tracer and hatchet, one or
both of which are moveable on the beam, so that the distance between the tracer
and the hatchet is adjustable.
2°. A planimeter constructed substantially as herein set forth, and as illustrated
in the accompanying drawings.
Dated this 2nd day of September 1891.
J. CLARK JEFFERSON,
2, East Parade, Leeds, Agent for Applicant.