IMPROVEMENTS IN TRIPOD HEADS FOR TRANSITS, LEVELS, THEODOLITES, AND OTHER INSTRUMENTS FOR SURVEYING, ENGINEERING, AND ASTRONOMICAL PURPOSES
Year: 1878

page_text: LETTERS PATENT to Arthur Davis, of Newgate Street, London, for the
Invention of "IMPROVEMENTS IN TRIPOD HEADS FOR TRANSITS, LEVELS,
THEODOLITES, AND OTHER INSTRUMENTS FOR SURVEYING, ENGINEERING, AND
ASTRONOMICAL PURPOSES." A communication from abroad by Daniel
Hoffman, of Philadelphia, Pennsylvania, United States of North America.
PROVISIONAL SPECIFICATION left by the said Arthur Davis at the Office
of the Commissioners of Patents on the 24th May 1878.
ARTHUR DAVIS, of Newgate Street, London. "IMPROVEMENTS IN TRIPOD
HEADS FOR TRANSITS, LEVELS, THEODOLITES, AND OTHER INSTRUMENTS FOR
SURVEYING, ENGINEERING, AND ASTRONOMICAL PURPOSES." A communication
from abroad by Daniel Hoffinan, of Philadelphia, Pennsylvania, United States of
North America.
This Invention has relation to improvements in tripod heads for transits, levels,
theodolites, and other instruments for surveying, engineering, and astronomical
purposes.
The object of the Invention is to devise a tripod head of such a construction
that it may be leveled with absolute accuracy and expedition, and may be adjusted
horizontally for bringing the centre of the instrument over a fixed point on the
ground, whatever be the nature of the same or its inclination, the accompanying
Drawings forming part of this Specification, and represents a sectional elevation
of the parts composing the improved tripod head.
The plate A, A, shifting plate c, c, (are to bring the plummet over a point) the
half ball D, D, and the levelling screws G, G, are common to all first class transits.
It will be observed however that besides the ordinary half ball D, D, (moved by
the levelling screws G, G,) there is an extra plate F, F, in which the nuts n, n,
(that carry the levelling screws) are placed; the upper part of this plate F, F, is
also a balf ball g, g. This extra plate F, F, always remains horizontal, no matter
how much the instrument (attached to plate E, E,) may require to be turned on its
D

page_text: ball g, g, in order to make the levels stand level. On the upper part of the plate
E, E, of which the small half ball D, D, forms a part, there is a cup or socket e, e,
that slides over and on the large ball g, g; these two half balls D, D, and g, g,
are almost two inches apart and of unequal diameter, the upper one g, g, having
three times the surface of the lower one D, D, and are half balls. To use this tripod
proceed as in any ordinary tripod provided with a shifting head for setting the
plummet, that is, unslack any two of the levelling screws G, G, (half a turn will be
ample); this will allow the shifting plate c, c, to be free from the plate A, A, and
the entire transit can be shifted in any horizontal direction until the plummet is
precisely over the fixed point; so far these proceedings are common to all transits
having a shifting head; but an examination of the Drawing will show that this
unslacking of two of the levelling screws G, G, has not merely loosened the shifting
plate c, c, but has also unclamped the large ball g, y, and small ball D, D, from their
respective sockets e, e, and the sockets in plate c, c, and this allows while setting
the plummet the entire instrument also to be approximately leveled by hand
without touching the screws G, G. This can be done in an instant by merely
taking hold of the instrument and moving e, e, over g, g, in any direction necessary;
the two levelling screws G, G, that had been unslacked are now made as tight as
they ordinarily are in using. This tightening effects several purposes; it brings the
plate F, F, (with g, g) up against e, e, and thus raises the tripod head and draws
c, c, against the lower side of A, A, and at one operation effects three important
objects, clamps the plummet shifting plate c, c, and binds the two half balls e, e,
and D, D; the levelling of the instrument may then be completed accurately by
using the four levelling screws G, G, in the ordinary way, a half turn of the screw
will be ample for this.
The plate E is provided with any known suitable means for securing the instru-
ments to it.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Arthur Davis in the Great Seal Patent Office on the 12th November
1878.
ARTHUR DAVIS, of Newgate Street, London. "IMPROVEMENTS IN ⚫ TRIPOD
HEADS FOR TRANSITS, LEVELS, THEODOLITES, AND OTHER INSTRUMENTS FOR
SURVEYING, ENGINEERING, AND ASTRONOMICAL PURPOSES." A communication
from abroad by Daniel Hoffman, of Philadelphia, Pennsylvania, United States of
North America.
This Invention has relation to improvements in "tripod heads" for transits, levels,
theodolites, and other instruments for surveying, engineering, and astromonical
purposes.
The object of this Invention is to devise a tripod head of such a construction that
it may be levelled with absolute accuracy and expedition, and may be adjusted
horizontally for bringing the center of the instrument over a fixed point on the
ground, whatever be the nature of the same or its inclination.
In the accompanying Drawings forming part of this Specification,-
Fig. 1 represents a top view of the tripod head; and Fig. 2 is a sectional
elevation of the same.
The nature of the Invention will be readily perceived from the following
description:-A represents the base plate of my improved "tripod head" having a
large central circular opening a and a flange a upon its under side, provided with
a coarse screw thread upon its inner face, by means of which the whole head is
secured to the tripod; B represents the carrier plate upon which the upper part of
the head is supported. This plate has a central opening 6 of circular form of less
diameter than the opening a of plate A; C represents a socket plate having a short
central neck c, in which the concave bearing surface c' of the lower ball-and-socket
joint is formed. This plate is passed from below inside of the flange a, and its neck
thrust through the opening a, b, of the base plate and of the carrier plate
respectively. The diameter of the neck c and of the orifice b of the plate B are
the same, and the neck fits snugly in said orifice. The ball D of the lower socket
joint is passed up through the neck, and its projecting screw threaded end d through
the levelling screw plate E. It is then screwed into the lower end of the neck c,
projecting downward from the plate F, to which the instrument is directly
attached.
The levelling screw plate E has a large central opening f, and on its upper face is
provided with a convex annulus g, which is received in and accurately fits a concave
socket h upon the under side of the plate F aforesaid. When the end d is screwed
into the neck c aforesaid the parts of the tripod head are coupled together.
The convex annulus g and the socket h form the upper ball-and-socket joint of
my improved head for tripods, and their curved surfaces and those of the lower ball-
and-socket joint are concentric; consequently, while the levelling screw plate is
motionless the instrument plate F has free universal movement upon the lower ball-
and-socket joint c', D, in the ball of which the centers of the curved surfaces of
both the upper and lower joints are coincident.
The neck e of the instrument plate and that of the ball, as aforesaid, are connected
together, and the axial line of the former if extended would pass through the center
of the latter, consequently, when the said plate is level, and the instrument properly
secured thereon, the center of latter must run in lino with the longitudinal axis
of the neck, and the centre of the ball, and the plummet line in the vertical
prolongation of the said axis.
By sliding the carrier plate A horizontally, the plummet may be brought directly
over the fixed point on the ground with great accuracy and expedition, thus
bringing the center of the instrument and the said fixed point in the same vertical
line.

page_text: By setting up the levelling screws G the level thus obtained, and the adjustment
of the center of the instrument over the fixed point on the ground, may be preserved
for any length of time whatever be the nature of the ground. Those levelling
screws extend through long screw threaded nuts I rigidly secured to the plate E
exactly at right angles thereto, and their lower ends bear upon the plate B, as shown,
consequently, they are not liable to become jammed in their bearings, to lose their
position with reference to plate E, nor to interfere with the base plate.
I operate the head as follows to obtain a level position for the instrument and
bring its centre in the vertical line of the fixed point on the ground :-I loosen any
two of the levelling screws which may be convenient (about one-half turn will be
sufficient), thereby letting down plate C sufficiently to clear it from the base plate,
and permitting the carrier plate B to be shifted in a direction horizontally, carrying
the levelling plate, the upper and lower ball-and-socket joints, and the instrument
plate with it until the instrument on the head is centered over the fixed point on
the ground. This being accomplished I level the instrument approximately by
hand and exactly by setting up the two levelling screws aforesaid, as may be
requisite. This causes the ball and socket to bind tightly upon each, and produces
the desired result.
It will be readily seen by persons versed in the art that the ball-and-socket joint
C and D, and the joint formed by the concave and convex pieces g and h, may be
modified, constructed, arranged, and combined with the other parts of the instru-
ment in different forms than those represented, and yet made to perform all the
functions of the said Invention, as herein-before described, by giving the instrument
an universal motion for levelling purposes, and a lateral or horizontal motion for
adjusting it to a giyen point. However, I consider such modifications, changes of
form, and arrangement of parts are einbraced within the scope of my improvement,
as berein-before described, and therefore I do not consider it necessary to give
illustrations and descriptions of the various modifications which may be employed.
Having now described the manner of constructing and working the said improve-
ment, what I claim is,-
1st. The combination with tho plate A, having central opening a, and the plate
C, having the socket c¹ extending through said opening of the ball D, having
threaded neck D, the levelling screw plate E, having ball g, and the instrument
plate F having neck c and socket h, substantially as specified.
2nd. The combination with the base plate A, having central opening a, and the
socket plate c, having neck c of the carrying plate B, having aperture & fitting said
neck, and the levelling mechanism of a tripod head, substantially as specified.
3rd. A tripod head having a ball-and-socket joint for the base plate combination,
with the instrument plate F, having a spherical bearing g, h, combined with said
ball-and-socket joint the levelling plate E, substantially as specified.
4th. A tripod head having a ball-and-socket joint C, D, and a spherical bearing
g, h, in combination with the instrument plate F, substantially as represented, or
their mechanical equivalents, for purposes herein-before mentioned.
In witness whereof, I, the said Arthur Davis, have hereunto set my hand and
seal, this Eighth day of November, in the year of our Lord 1878.