Improvements in Instruments for Measuring Angles and Range Finding.
Year: 1885

page_text: PROVISIONAL SPECIFICATION.
Improvements in Instruments for Measuring Angles and
Range Finding.
JAMES HENRY STEWARD 406 Strand London Optician WILLIAM DREDGE
10 Buckingham Street, Strand, Civil Engineer, do hereby declare the nature of
our invention for IMPROVEMENTS IN INSTRUMENTS FOR MEASURING ANGLES &
RANGE FINDING, to be as follows:-
The application of a moveable base, arm, frame, or equivalent mount to carry
the index glass of a sextant or other reflecting instrument of that class and with
it the screw, rack, slide or other appliance by which it is moved, so that while the
movement permits of an arc of a circle being described around the other mirror
(the horizon glass) the relative position of the index mirror, & screw, rack, slide, or
other appliance is not altered. This in practice permits of objects being taken for
the purpose of alignment in measuring angles & range finding that are many
degrees removed from a right-angle (90°) without an error occuring.
J. H. STEWARD.
WILLIAM DREDGE.

page_text: The letters of reference are the same in each of the figures 1. 2 & 3.
A. is the case which contains the apparatus.
D. Horizon glass fixed to Case.
F the Index Glass fixed to the moveable limb L concentric with the pivot
P. on which the limb turns. B is a lower limb moving round the same axis
influenced by the screw E, but controlled and kept firmly in any position by the
Spring O. Affixed to this limb is a boss C through which a micrometer screw H.
works which acting on the limb L gives motion to it. The Spring M which is
fixed to the lower limb B presses on L & keeps it always against the screw H.
The Boss C. carries a bar index K graduated from 0 to 5 on either side of the zero
line and reading hundreds. To the screw H is fixed a drum G. divided first by a
meridian line m, and by the graduated Cross lines into one hundred equal parts-
on one side of the meridian line from 0. 1. 2 to 9 on the other 0. 9. 8 to 1-and
then in reading the index marks tens and units. This is shewn in figs. 1 & 2—
thus any motion of the lower limb round the pivot carries with it the upper limb
without registering-whilst a motion of the upper limb may be made independently-
and the angle registered by the index.
Fig. 3. shews a modification of the drum G and index bar K. in which neither are
graduated the latter acts as a stop & the wheel N shews a gap in the periphrey-
(or if of any other shape, in the arc described)-which limits the action of the
screw to the travel of this gap, & is applicable to an instrument having no lower
limb B & that measures by fixed angles, one of which is 90°; as well as the one
previously described with moveable lower limb.
The Section on r. 8 fig. 2 shews the manner by which we ensure a perfect
optical square and of correcting any error in the permanent adjustment that may
arise in use as follows-If when the instrument is in temporary adjustment (as
presently described) it is found by testing that it does not reflect an angle of
exactly 90° turn the screw H until it does, when the reading will mark extent of
error, next slacken the Clamp Screw a & with key provided turn screw b until the
1+7

page_text: line e coincides with the meridian line m. (we sometimes use a pointer coming up
to the meridian line for this purpose) the permanent adjustment is then correct
The ordinary adjustment is as follows
1st Turn the screwhead N till the meridian and zero lines on the drum coincide
with the zero line on the bar index K.
2nd Turn the screw E until the line e coincides with the meridian line m. when
the instrument will reflect a perfect right angle.
In fig. 4 which illustrates a use of the instrument the operator is supposed to be
at A and the distance of B from that point is required. Select some mark D as
nearly at right angles with A. B. as convenient-look through instrument at B.
and turn screw E till D is brought to coincide by reflection with B. Measure A. C—
& at C again look at B & turn Screwhead N till reflection of D again coincides
with B. the reading of the index then referred to a table affixed too or accompanying
the instrument gives the range A B.
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
1st The application of a lower limb B to instruments for reflecting & measuring
angles on principles similiar to the Sextant, and range finders of that class-with
movements & parts substantially as shewn & described.
2nd The modifications for controlling the traverse of the Screw H either with or
without the lower limb B so as to measure a fixed angle.
3rd The method shewn for obtaining a perfect Optical Square.