Year: 1897

page_text: Date of Application, 27th May, 1897-Accepted, 21st Aug.,
1897
I CHARLES LOUIS HETT of Springfield, Brigg in the County of Lincoln 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:-
Whereas in levels of the suspended Mirror type, as hitherto made, the staff is seen
by direct vision, and is compared with the reflexion in the suspended Mirror, either
of the pupil of the eye or of marks on a small card pierced with a slit or hole
through which the sight is taken. The staff is fitted with a vane which is adjusted
by the man, in compliance with signals given by the surveyor, until it corresponds
with the reflection of the pupil of the eye or of the marks on the card as the case
may be.
The position of the vane on the staff is then read at close quarters.
In my invention the vane on the staff is dispensed with and the staff is read direc
in the same manner as when an ordinary dumpy level is employed. I accomplish
this as follows. The image of the staff is received on a suspended mirror set at an
angle of 45° with its axis and adjusted to hang plumb. When a line between the
staff and the mirror is at right-angles to its axis, it follows that the point in the staff
which is at the same level as the axis is reflected along the centre line of such axis.
This reflexion is again reflected by a second mirror fixed to the frame of the level at
an angle of 45° through the centre of a small telescope, such as are used in dumpy
levels, and read on the spider webs in the usual manner. The axis of the telescope
cuts the axis of suspension of the suspended mirror, at right angles at the point
where the reflecting surface of the fixed mirror cuts the axis of suspension at an
angle of 45°. Hence the point of the staff which is level with the axis of suspension,
will remain stationary on the spider webs if the telescope is inclined. Therefore
the level stand only requires to be set fairly level by eye and the reading taken
without further adjustment.
My invention is further explained by the accompanying drawings which I shall
now describe.
Figs. 1-2 and 3 represent respectively a longitudinal sectional elevation a cross
sectional elevation and a plan partly in section.
A is the suspended mirror, which reflects the image of the staff, in the direction
of its own axis. B is the mirror, attached to the frame, which transmits the image,
of the staff through the telescope C. d, d, d, d, d, and d are set screws for adjusting
the mirrors, e, e, e, and e are light springs, which give way as the above named set
screws are screwed in. f and fare set screws carrying the pivots of the suspended
mirror frame. g and h are springs which prevent the oscilation of the suspended
mirror frame when not in use. i is a shutter for closing the aperture, through which
the staff is viewed. In closing this shutter a projection presses the spring upon the
lower portion of the suspended mirror frame, and presses it against the spring h,
where it is gently, but firmly held, until the shutter i, is again opened.
and kare

page_text: metal loops which drop over the taper top of a light tripod and support the level
when in use, is the milled head for focussing. m is the diaphragm carrying the
spider webbs. n is the object glass of the telescope, and o is the eyepiece.
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 :-
The combination of a telescope, fitted with spider webs or their equivalent,
with a fixed and a suspended mirror, in the manner and for the purpose described.
Dated this 24th day of May 1807
CHARLES LOUIS HETT.