AN IMPROVEMENT OR IMPROVEMENTS IN THE CONSTRUCTION OF BRIDGES MADE OF IRON OR OTHER MATERIALS, WHICH INVENTION IS ALSO APPLICABLE TO OTHER USEFUL PURPOSES
Year: 1833

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JAMES
MACDONALD, of the University Club House, Pall Mall East, in the Parish of
Saint Martin in the Fields, in the County of Middlesex, Gentleman, send
greeting.
WHEREAS His present most Excellent Majesty King William the Fourth,
by His Letters Patent under the Great Seal of Great Britain, bearing date
at. Westminster, the Twenty-fourth day of January, One thousand eight
hundred and thirty-three, and in the third year of His reign, did, for Himself,
His heirs and successors, give and grant unto me, the said James Macdonald,
His especial licence, full power, sole privilege and authority, that I, the said
James Macdonald, my executors, administrators, and assigns, or such others
as I, the said James Macdonald, my executors, administrators, or assigns,
should at any time agree with, and no others, from time to time and at all
times during the term of years therein mentioned, should and lawfully might
make, use, exercise, and vend, within England, Wales, and the Town of
Berwick-upon-Tweed, my Invention of "AN IMPROVEMENT OR IMPROVEMENTS
IN THE CONSTRUCTION OF BRIDGES MADE OF IRON OR OTHER MATERIALS, WHICH
INVENTION IS ALSO APPLICABLE TO OTHER USEFUL PURPOSES," which Invention was
communicated to me by a certain Foreigner residing abroad; in which said
Letters Patent is contained a proviso obliging me, the said James Macdonald,
by an instrument in writing under my hand and seal, particularly to describe
and ascertain the nature of the said Invention, and in what manner the same
is to be performed, and to cause the same to be inrolled in His said Majesty's
High Court of Chancery within six calendar months next and immediately.

page_text: after the date of the said in part recited Letters Patent, as in and by the
same, reference being thereunto had, will more fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
James Macdonald, do hereby declare that the nature of the said Invention,
and the manner in which the same is to be performed, are particularly described
and ascertained in and by the Drawings hereunto-annexed, and the following
description, that is to say:-
These improvements in the construction of bridges or arches made of iron,
or other materials, are founded upon the same principles as those set out in
the Specification of a Patent granted to me for "An Improved Construction
of Railway," dated the Twenty-ninth day of June, One thousand eight hundred
and thirty-two, which Specification was duly inrolled in Chancery, in the Office
of the Rolls' Chapel, on the Twenty-ninth day of December, in the same year,
and to which Specification I refer the better to elucidate the principles of the
present Invention.
These improved bridges or arches I. construct by combining series of iron
bars or ribs so arranged and connected as to sustain or support the pressure
and tension of each other, the whole, when combined, constituting an expanse
of framework in the form of the segment of a polygon or arch, upon the
upper surface of which framework the floor of the bridge or carriage way, or
covering of a roof, is to be laid. The principle on which the tension and
support of the framework is, founded may be illustrated by reference.to the
principle of construction in the rafters, tie beam, and ring post of roofs, the
structure of the bridge consisting of combined rafters with. tie beams and ring.
posts intersecting each other, and connected; in parallel ranges. by transverse
bolts and diagonal braces; for the purpose of firmly securing the whole
structure.
In the accompanying Drawings Figurefl: représents: a combination of hori
zontal, diagonal, and perpendicular bars or rails, secured by screw nuts: at
their junctions. This combination of bars? or rails constitute two elementary
portions of the arch, each of which portions. I call a bay. A series of these
portions, when connected in a range, produce the arch shewn at.Figure 2.
These bars or ribs I prefer to form of malleable iron by means of rolling,
their dimensions of course depending upon the magnitude of the bridge: to be
erected, and may be formed with projecting ribs on their sides, if necessary,
to give additional strength. These series of bays or elementary portions are to
be combined in pairs in the way described in my former Specification, and
connected together by transverse bolts and diagonal braces, which, when so
combined, constitute an expanse of framework in the form of an arch. In

page_text: constructing these.improved. bridges I employ two; four, or more of such pairs
of arches. of framework placed side by side in parallel ranges, at proper.
distances; according to the required: strength of the bridge, which arches of
framework I.connect by diagonal bracings or stretchers; or both, in the manner
shewn in Figure 3, which is the plan. view of the frame of a bridge, consisting
of two pairs of arches. of framework, or four series of bays or elementary seg-
ments; and also in Figure 4, which.isva transverse section taken across the
bridge, but drawn on the same scale as Figure 1. The manner of combining
the several bars or ribs in constructing, the elementary portions or bays of the
framework, and also the continuous connections of the same to form any given
length of framework and to constitute: an arch; having been explained in my
former. Specification, I shall proceed to describe the manner in which the
several pairs of arches: of framework are to be connected to form the frame-
work of an entire bridge.
In Figures 3 and:4, a, a, b, b, are four series of bays of framework, that is,
two and two connected together in pairs by transverse stretcher bolts c, c, and
diagonal pieces d, d; and firmly secured or braced together by the screw nuts
on the ends of the stretcher bolts. This connection of the sides or ranges of
framework may also be further strengthened by the plates k, k, which are
intended to support the flooring or carriage way of the bridge. The several
pairs of arches ofs framework, are connected together by horizontal and vertical
diagonal pieces e; e, and f, f, placed between the pairs, and. secured by screw
nuts on the ends of the stretcher bolts c;:c, or instead of horizontal diagonal'
pieces.stretcher bolts:g, g, may be used for the same purpose with good effect,
or. both may be employed, as shewn in Figure 3.. h, h, are the top rails, which
are formed by two. rebated pieces connected at the top of the framework by.
screw.nuts and collars. i is the curb fixed upon the top rails supporting the:
balustrades, and the ends of the plates k, k, upon which the roadway is to be
formed, also, bear upon the top rail. It will be obvious that from the peculiar
mode of combining the several parts of the framework; and from the manner
in which the several portions tend to support each other and produce a nearly
equal tension and compression of all the parts, bridges with very flat arches
may be constructed upon this improved plan; and as the spring or rise of the
arch may be varied to: suit the length or span, or the design of the builder, I'
need only remark that all the perpendicular bars (or those which correspond
to the king posts of a roof) must be in the position of radii from the centre of
the circle of which, the arch, is a segment, therefore the distance between the
upright bars 1, 1, will be greatest at the point where they unite with the top
rails h, h; and the length of the top rails being determined by the length and
spring of the arch or segment, the relative length of the middle and lower tie

page_text: bars or chains m and n must always depend on the length of the upright bars 1, 1
(or depth of the bridge), and consequently the distance between the holes made in
the diagonal bars of the framework o, o, for the bolts c, c, to pass through in
connecting them to the middle and bottom tie beams or chains m and n will
be less than the distance between the holes made in the same diagonal bars
for the bolts of the middle tie chain n and top rail h to pass through.
Figure 5 is a plan view of a portion of the lower tie chain n; and Figures 6
As the bridge
and 7 are views of a portion of the middle tie chain or beam m.
is intended to support its own weight by the tension of the middle and lower
range of tie bars or chains, it may be erected upon piers at its ends, which
merely sustain the downward pressure; but as these improved bridges are
intended to depend upon the two principles of tension and resistance, I propose
to raise abutments upon the end piers; therefore, in constructing these improved
bridges, I cause the ends of the top rail and middle tie beam to bear against
the abutments p, p, but leave a small space between the end of the bottom tie
beam or chain n and the abutment (as shewn in the Drawing), in order to
allow of its extending, as the deflection of the arch takes place, on any super-
incumbant weight passing over the bridge, or by the expansion and contraction
of the metal under variations of temperature.
Figure 8 is a side elevation of a bridge, the roadway of which is made level
by supporting it upon pillars or spandrils extending from the top rails or frame
work of the bridge. It will be evident that arches of framework constructed
upon this improved plan, from their capability of sustaining their own weight
when resting upon piers without lateral abutments, may be used to form the
framework for roofs of buildings with good effect; and also that the same
description of arches of framework may be used to support aqueducts, viaducts,
and such other purposes, but which it will not be necessary for me particularly
to describe, as the same principle of construction is used in all.
And lastly, I wish it to be understood that I do not claim the exclusive use
of any of the parts herein employed, if taken separately and applied to other
purposes than the erection of bridges or arches, for roofs of buildings, aqua-
ducts, and viaducts; but I do claim as the subject of this Invention the com-
bination of the said parts when applied to the construction of bridges or arches
of framework possessing the advantages of both the principles combined of
tension and lateral resistance.
In witness whereof, I, the said James Macdonald, have hereunto set my
hand and seal, this Twenty-fourth day of July, One thousand eight
hundred and thirty-three.
JAS (L.S.) MACDONALD.

page_text: AND BE IT REMEMBERED, that on the Twenty-fourth day of July, in
the fourth year of the reign of His Majesty King William the Fourth, the
aforesaid James Macdonald came before our said Lord the King in His
Chancery, and acknowledged the Instrument aforesaid, and all and every
thing therein contained and specified, in form above written. And also the
Instrument aforesaid was stamped according to the tenor of the Statute made
in the fifty-fifth year of the reign of His late Majesty King George the Third.
Inrolled the Twenty-fourth day of July, One thousand eight hundred. and
thirty-three.