Improvements in Lanterns for Lecturers and others and in Appliances connected therewith.
Year: 1890

page_text: Date of Application, 15th Aug., 1890
Complete Specification Left, 15th May, 1891-Accepted, 20th June, 1891
PROVISIONAL SPECIFICATION.
Improvements in Lanterns for Lecturers and others and in
Appliances connected therewith.
I, DAVID GRAVELL, of 6 Queen Anne's Gate, in the City of Westminster,
Civil Engineer, do hereby declare the nature of this invention to be as follows:-
According to this invention a spot or disc of light is cast upon the diagram under
consideration the spot having at about its middle the point of a shadow this point
being directed to the part of the diagram to which it is desired to draw attention.
The apparatus consists of a lantern having within it a source of light preferably
the oxyhydrogen lime light, the ray passing out through a small aperture in a
diaphragm which is provided with a radial arm or pointer extending from the
circumference to about the centre of the aperture. In front of the diaphragm is
a lens which condenses the ray into a suitable cylindrical or conical form. This
lens is carried in a sliding tube so that its distance from the aperture can be varied
to regulate the size of the spot of light upon the diagram.
The lantern is preferably mounted upon one end of a lever whose other end is
provided with a counterbalance weight. This lever is free to turn about a horizontal
pivot on the top of an upright rod which is free to turn about its own axis in a
foot or stand. The lecturer by holding the counterbalance weight can thus turn
the lantern either in a vertical or horizontal plane.
Deted this 15th day of August 1890.
DAVID GRAVELL.
COMPLETE SPECIFICATION.
Improvements in Lanterns for Lecturers and others and in
Appliances connected therewith.
I, DAVID GRAVELL, of 6 Queen Anne's Gate, in the City of Westminster,
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 :-
According to this invention apparatus is so arranged that a spot or disc of light
In this
may be cast upon a diagram displayed upon a wall or suitably suspended.
light spot, at about its middle, appears the image or shadow of a pointer and by
suitably directing the apparatus the extremity of the shadow may be thrown upon
the part of the diagram to which it is desired to draw attention.
The apparatus consists of a lantern having within it a source of light preferably
the oxyhydrogen lime light. The ray from the source of light passes out through
a small aperture in a diaphragm in which a needle point is fixed radially to extend
In front of the
from the circumference to about the centre of the aperture.
diaphragm is a lens which condenses the ray and focuses the indicating shadow
upon
the diagram. The lens is carried in a tube which slides to adjust the focus. The
lantern is preferably mounted upon one end of a lever whose other end is provided
with a counterbalance weight. This lever is free to turn about a horizontal pivot
on the top of an upright, and the upright can be turned about its own axis in a foot
or stand. The lecturer holding the lever by the counterbalance at its extremity
can move the lantern and direct it as he pleases so that the point of the indicating
shadow may move in accordance with the verbal description of the diagram.
In order that my said invention may be fully understood and readily carried into
effect I will proceed to describe the drawings hereunto annexed.

page_text: . DESCRIPTION OF THE DRAWINGS.
Figure 1 is a side elevation of apparatus constructed in accordance with my
invention.
Figure 2 is a vertical section of a portion of the same to a larger scale.
is a
is
a is the body of the lantern from it there extends horizontally a tube b, on
which slides an outer tube carrying the lens dat its extremity. At the inner end
of the tube is the diaphragm e in which there is a small central aperture.
needle point fixed to the diaphragm and extending partly across the aperture.
a pipe conveying an inflammable gas preferably hydrogen or common coal gas into
the lantern is another pipe partly within the pipe and conveying oxygen gas.
These pipes terminate in two concentric orifices or it might be in one single orifice
which then constitutes the burner. is a support for a cylinder of compressed
lime, it is mounted upon a slider on the bottom of the lantern admitting of the
lime cylinder being moved to and from the burner and also raised or lowered. The
pipes are provided with stop cocks and have flexible connections and the adjustment
of the parts is such that the spot on the lime cylinder which is most brilliantly
incandescent is aligned with the centres of the diaphragm aperture and the lens.
The lantern is fixed at the extremity of the lever which is pivotted at the
upper end of the forked support Z. mis a counterpoise it has a stem m' which
enters within the outer end of the lever & this part being made tubular to receive
it. The forked support is also tubular at its lower end and it fits over and upon
a vertical pin or stem fixed in the base n. Clamping screws are provided at o
and P the former when screwed up prevents horizontal movement of the lantern and
the latter prevents vertical movement.
In some cases I provide a condensing lens between the source of light and the
diaphragm to focus the light in the aperture, but this is not required wliere the
source of light is brought sufficiently near to the aperture.
For some purposes I provide a pencil at the extremity of the stem of the
counterpoise m; it is pressed outwards by a spring which holds it when in use in
contact with a surface of paper upon a drawing board set up behind it. Then as
the shadow pointer is made to follow along any line a corresponding line will be
traced on the paper. Thus a diagram may be copied or the interior of a building
automatically drawn.
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 lantern for projection for the use of lecturers and others, mounted upon a
support which permits it to be directed as desired and containing a source of light,
a diaphragm with an aperture, a needle pointer projecting more or less across the
aperture and a lens which will focus the image or shadow of the pointer upon a
diagram or surface at a distance from the lantern.
Dated this 14th day of May 1891
DAVID GRAVELL.