An Improved Sight Testing Apparatus.
Year: 1891

page_text: Date of Application, 15th May, 1891
Complete Specification Left, 10th Dec., 1891-Accepted, 30th Apr., 1892
PROVISIONAL SPECIFICATION.
An Improved Sight Testing Apparatus.
CHARLES KAHN and WALTER DANGERFIELD both of No. 138 Strand in the
County of London trading as the National Silex Optical Company Opticians
do hereby declare the nature of this invention to be as follows:-
A machine giving an intermittent or eccentric revolutionary movement to a card
or disc on which lines are drawn & so that the card or disc remains stationary for
a few seconds at different angles.
This result being obtained as follows-An ordinary electric motor is employed
the spindle of the wheel of which passes through an upright support and has a
small cog-wheel affixed thereto this is in contact with and when in motion revolves
a double cog-wheel having cogs all round on the edge or side nearest to & in
contact with the small cog-wheel but only one twelfth of the number of cogs on
the outer edge or side. Another continuous cog-wheel is fixed above the double cog-
wheel in such a position that it is only in contact with the double cog-wheel when
the revolutions thereof bring the cogs on the outer edge in contact therewith. A
projecting arm is fixed on the upper cog-wheel and revolves therewith, to this arm
the card or disc is affixed.
The invention being worked by an ordinary bichromate battery & with switch
connections enables the operator to test sight for astigmatism without standing at a
distance from the patient.
Dated this 15th day of May 1891.
CHARLES KAHN.
WALTER DANGERFIELD.
COMPLETE SPECIFICATION.
An Improved Sight Testing Apparatus.
We CHARLES KAHN and WALTER DANGERFIELD of 138 Strand in the
County London Opticians 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 is for testing the defects of astigmatism and to enable the operator
to so test without leaving the side of the patient.
A set of wheels so arranged as to give when in motion an intermitting
revolutionary movement to a card or disc attached thereto and on which parallel
lines are drawn and so that the said card or disc remains stationary for a few
seconds at differing angles. This result is obtained as follows-
An ordinary electric motor is employed the spindle of the driving wheel (A) of
which passes through an upright support and has a small cog-wheel (B) affixed
thereto, this when in motion turns a double cog-wheel (C) fixed to the said
upright support above the small cog-wheel the double cog-wheel has cogs all
round the inner edge which is in contact with the small wheel but only one twelfth
or some smaller proportion of cogs on the outer edge which is not in contact with
the small cog-wheel. Another cog-wheel E is fixed to the upright support above
the double cog-wheel in such a manner that the teeth or cogs thereof are not in
contact with the double cog-wheel except when the revolutions thereof bring the
smaller number of cogs on the outer edge thereof in contact with the topmost cog-
wheel which is then partly revolved and then remains stationary until the double
cog-wheel has again revolved. The card or disc is fixed to the uppermost cog-

page_text: wheel by means of a projecting arm or spindle G which revolves with the cog-
wheel.
The invention is connected to the battery by switches enabling the operator to
shut off the power and so stop the revolutions of the wheels whenever desired.
.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
1. In sight testing machines a set of wheels arranged and in combination with a
card or disc as hereinbefore described and connected with an electric battery as
before described enabling the operator to test sight for astigmatism without leaving
the side of the patient.
Dated this 30th day of November 1891
CHARLES. KAHN.
WALTER DANGERFIELD.