A New or Improved Spherometer.
Year: 1894

page_text: [Communicated from abroad by JOSUE HEILMANN and RODOLPHE SIMON,
19, Rue Cambon, Paris, France, Engineers.]
A New or Improved Spherometer.
I, WILLIAM GEORGE HEYS of 70 Market Street Manchester in the County of
Lancaster, 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 relates to apparatus for measuring and indicating the curvature
of spherical surfaces either concave or convex.
The accompanying drawings to which reference is made hereinafter illustrate in
what manner the improved apparatus may be constructed and applied, similar
letters being used to indicate similar parts where they occur in the different
figures.
Figure illustrates the apparatus in front elevation.
Figure 2 shews it with the dial removed and the mechanism exposed.
Figure 3 represents a transverse section of the casing and a side elevation of the
mechanism.
Figure 4 illustrates the application of the apparatus to a spherical surface.
In the centre of the plate P is mounted a shaft a carrying a needle or pointer b
and furnished with a pinion e which is operated by a toothed segment d. This
segment is pivoted or centred at e and has an arm or extension to which is pivoted
at one end of connecting rod g the other end of which is attached to the rod h
sliding in the guides i and k. The up and down motion of the rod h communicates
a to and fro motion to the segment d. The rod h terminates in a rounded or
blunt points and passes longitudinally through the centre of a cylinder or
annular chamber I made in one piece with the plate P and perpendicular to
it. The rod h is divided into two parts the upper one square and the lower
one round and its length may be regulated by the screw m attached to one of
the halves and entering the other as a nut. The lower round half of the rod
is provided with a square or other device so that it can be turned by means of
a key when it is desired to increase or diminish the length of the rod. Attached
to the shaft a is a spiral or other suitable spring n which through the inter-
mediary of the toothed segment d and the connecting rod g tends to push the
rod to the outside of the annular chamber l. The length of the rod h is
regulated to such an extent that its point is in the same plane as the edge of the
chamber when the needle or pointer is in the mean or zero position upon the
dial C. Two pins rr fixed upon the plate P limit the motion of the segment d
and consequently that of the needle.
When the edge of the annular chamber is resting upon the surface of a
spherical body such as either a convex or concave lens, the rod is pushed inwards
to a certain extent which is indicated by the needle on the dial. If the surface is
concave the point s rests without or below the plane as illustrated by Figure 4
and the needle indicates upon one side of the dial the pitch of the arc o—a—o.
If, on the contrary, the surface to be measured is convex, the point s passes through
the plane into the chamber and the needle indicates upon the other side of the
dial the pitch of the arc o-b-o.
-
Knowing the pitch and the diameter of the annular chamber a very simple
calculation permits of the deduction of the radius of curvature of the spherical part
and as a consequence in the case of a lens, the focal length. These numbers may

page_text: if desired be placed upon the dial in substitution for or in addition to those
indicating the pitch.
The whole of the mechanism is contained within a casing p provided with a
glass through which the dial and the needle are visible.
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 :―
A spherometer constructed arranged and operating substantially as hercinbefore
described and as illustrated by the accompanying drawings.
Dated this 25th day of August A.D. 1894.
WILLIAM GEO. HEYS.