IMPROVEMENTS IN ENGINEERS' REVERSIBLE LEVELS
Year: 1884

page_text: We, CHARLES FREDERICK COOKE and THOMAS COOKE, both of the Firm of
"Messrs T. Cooke and Sons," Buckingham Works, Bishophill, York in the County
of York, Opticians and Engineers &c. do hereby declare the nature of our
invention for IMPROVEMENTS IN ENGINEERS' REVERSIBLE LEVELS and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement:-
In the accompanying diagram, L-L' is the telescope, (shewn in section at Fig. 1.)
in one end of which (L) screws or otherwise fits the object-glass and in the other
end the eyepiece with the usual crosslines in its focus. The eye-end is made to
approach or recede from the object-end (for the purpose of focussing) in the usual
manner. Fixed on the outer telescope tube are the two flanges F & F', which are
both turned carefully to one cylindrical surface, having its axis coincident with the
opitical axis of the telescope.
Fig 2. is a longitudinal section of the socket (into which the telescope fit³)
together with its base-plate P-P, to which latter the vertical axis of the instrument
is fixed. This axis (B) is adjusted to perfect perpendicularity in the usual manner
by means of the three adjusting screws which work through the arms of the tribrach,
as shewn.
The socket S-S' is formed by two endpieces, which are separated by the same
distance as the flanges F & F¹ and turned inside to one cylindrical surface of such
a diameter as will allow them to perfectly fit over the flanges F & F of the telescope
and allow the latter to be inserted lengthwise from either end of the socket until it
shall be driven home as far as the stop-flange (ST. Fig 1.) will allow. The telescope
may be further secured by the two screws (Sc.) shewn in Fig. 3., where the
instrument is represented as complete and ready for use.
The two end pieces of the socket are rigidly joined together by the tubing T-T,
which keeps them in an exact straight line with one-another. The socket, with its
attachment to the base-plate P-P and means of adjustment, is shewn in end
elevation in Fig. 4. One end only is raised or lowered by means of the adjusting
lock-nuts N & N. The bottom of the other end of the socket is very slightly
rounded off and held firmly down by screws through the base-plate P-P, which
however, do not prevent the small amount of rocking movement which must
necessarily accompany the raising or lowering of the other end of the socket. On
the top of the socket is fixed the usual sensitive bubble tube, which is a justible
(with respect to the socket) in the manner found most suitable for these instruments,

page_text: It is evident that the perfect adjustment of the instrument may be effected at any
time and place (if found necessary) by first directing the telescope to a convenient
test-mark and then raising or lowering the adjustible end of the socket until the
telescope (which must be correctly collimated in the first place; that is, having its
crosslines in such adjustment that the turning of the telescope 180° round in its
socket shall not affect their position with respect to the image of the test-object)
shall cast exactly the same point of the image of the test-object onto the crossing
of the lines in the eye-end indifferently as to whether the telescope be inserted first
through the one end or first through the other end of the socket before being pushed
home. By this means the telescope is adjusted so that its axis of collimation is
perpendicular to the vertical bearing B. If, now, the axis B be adjusted to
perpendicularity by means of the foot-screws of the tribrach and the sensitive level,
and the bubble of the latter made to occupy the centre of its run, then the
instrument is in its working condition. Having now particularly described and
ascertained the nature of our said invention and in what manner the same is to
be performed, we declare that what we claim is :-
In an Engineers' reversible Level, the use and employment of the socket S-T-S¹
together with its means of adjustment; into which socket a detached but complete
telescope can be introduced end wise from either end, and held there in manner and
for purposes substantially as herein described and shewn in the drawings; the
embrace or fit of the socket round the telescope either being confined to flanges at
each end (as in drawings) or extending more or less throughout the length of the
socket.