IMPROVEMENTS IN COUNTERBALANCED LIFTING BRIDGES
Year: 1873

page_text: LETTERS PATENT to Walter Raleigh Browne, of No. 6, Delahay Street,
in the City of Westminster, for the Invention of "IMPROVEMENTS IN
COUNTERBALANCED LIFTING BRIDGES."
Sealed the 17th October 1873, and dated the 17th May 1873.
PROVISIONAL SPECIFICATION left by the said Walter Raleigh Browne
at the Office of the Commissioners of Patents, with his Petition,
on the 17th May 1873.
I, WALTER RALEIGH BROWNE, of No. 6, Delahay Street, in the City
of Westminster, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN COUNTERBALANCED LIFTING BRIDGES," to be as follows:-
This Invention relates to the class of bridges which are opened by
being lifted into an erect position after the manner of the ancient draw-
bridges.
In order to facilitate the operation of lifting it is usual to make the
jib end and heel end of the bridge balance cach other round the shaft or

page_text: axle. It is in the arrangement of this counterbalancing that the
present Invention consists. The counterweight in this case is not
attached to the bridge, so as to form part of it, but is contained in a
separate pit or chamber placed some distance behind the heel of the
bridge. This counterweight may consist of a cast-iron box filled with
sand, water, or other convenient material. To each end of this box a
chain is attached which passes over a pulley at the top of the pit or
chamber, and is thence led to the point of attachment to the bridge.
This point of attachment should be over the axle of the bridge and at
a considerable height above it, so as to give a suitable leverage to the
pull of the chain. This height may be obtained by placing the axle
below the bottom of the bridge girders, and by using a bracket or
standard bolted to the top of the outside girder, to which the chain may
be attached. It will then be seen that supposing the moment round
the axle of the weight of the bridge to be equal to that of the pull on
the chain when the bridge is down then as soon as the bridge is raised the
moment of the pull acting at a longer arm will be greater than that of
the weight and will therefore continue the motion of itself. The point
of attachment should be so arranged that when the centre of gravity
of the bridge is vertically above the axle the line of the chain produced
may also pass through the axle or nearly so, so that the two moments
may be zero about the same time. From this point the moment of the
chain still acting in the contrary direction to that of the weight of the
bridge will tend to stop the bridge or to destroy the motion previously
given, and as it will again have a preponderance over the moment of the
weight the bridge may be brought to rest at its proper position when
fully open. In closing the bridge the same effects will be produced, the
counterweight accelerating the motion of the bridge in the first half
of its travel, and retarding in the second, so as to bring it to rest in its
original position.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Walter Raleigh Browne, in the Great Seal Patent
Office on the 17th November 1873.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WALTER
RALEIGH BROWNE, of No. 6, Delahay Street, in the City of Westminster, 3
send greeting.

page_text: WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Seventeenth day of May, in the year of
our Lord One thousand eight hundred and seventy-three, in the thirty-
sixth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Walter Raleigh Browne, Her special
license that I, the said Walter Raleigh Browne, my executors, admini-
strators, and assigns, or such others as I, the said Walter Raleigh Browne,
my executors, administrators, and assigns, should at any time agree with,
and no others, from time to time and at all times thereafter during the
term therein expressed, should and lawfully might, make, use, exercise,
and vend, within the United Kingdom of Great Britain and Ireland, the
Channel Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN
COUNTERBALANCED LIFTING BRIDGES," upon the condition (amongst others)
that I, the said Walter Raleigh Browne, my executors or admini-
strators, by an instrument in writing under my, or their, or one of
their hands and seals, should particularly describe and ascertain the
nature of the said Invention, and in what manner the same was to
be performed, and cause the same to be filed in the Great Seal Patent
Office within six calendar months next and immediately after the date
of the said Letters Patent.
NOW KNOW YE, that I, the said Walter Raleigh Browne, do hereby
declare the nature of the said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in and
by the following statement thereof, that is to say :-
This Invention relates to the class of bridges which are opened by
being lifted into an erect position after the manner of the ancient
drawbridges.
In order to facilitate the operation of lifting it is usual to make the jib.
end and heel end of the bridge balance each other round the shaft or
axle. It is in the arrangement of this counterbalancing that the prosent
Invention consists. The counterweight in this case is not attached to the
bridge, so as to form part of it, but is contained in a separate pit or
chamber placed some distance behind the heel of the bridge. This counter-
weight may consist of a cast iron box filled with sand, water, or other
convenient material. To each end of this box a chain is attached which
passes over a pulley at the top of the pit or chamber, and is thence led
to the point of attachment to the bridge. This point of attachment should
be over the axle of the bridge and at a considerable height above it, so as

page_text: to give a suitable leverage to the pull of the chain. This height may
be obtained by placing the axle below the bottom of the bridge girders,
and by using a bracket or standard bolted to the top of the outside
girder, to which the chain may be attached. It will then be seen that
supposing the moment round the axle of the weight of the bridge to be
equal to that of the pull on the chain when the bridge is down then as
soon as the bridge is raised the moment of the pull acting at a propor-
tionally longer arm will be greater than that of the weight and will
therefor continue the motion of itself. The point of attachment should
be so arranged that when the centre of gravity of the bridge is vertically
above the axle the line of the chain produced may also pass through the
axle or nearly so, so that the two moments may be zero about the same
time: From this point the moment of the chain still acting in the
contrary direction to that of the weight of the bridge will tend to stop
the bridge or to destroy the motion previously given, and as it will again
have a preponderance over the moment of the weight the bridge may be
brought to rest at its proper position when fully open. In closing the
bridge the same effects will be produced, the counterweight accelerating
the motion of the bridge in the first half of its travel, and retarding in
the second, so as to bring it to rest in its original position.
In ordon that me soid Invention
may be most fully understood and

page_text: its axis is a beveled pinion gearing with a similar pinion on a vertical
axis, and this axis by a similar pair of pinions turns a spur pinion which
is in gear with a toothed wheel upon the axis of the bridge.
The bridges are provided with ordinary locking bolts when set for
traffic, but these are not shown in the Drawing.
To aid in controlling the bridges a brake wheel may be fixed on the
axis of cach of them, and a treadle may conveniently be used to tighten
the brake strap upon the wheel when it is desired to check the bridge.
These bridges have the advantage over ordinary lifting bridges in that
for a given opening the bridge is shorter, both because the axis is placed
nearer to the edge, and also because the overhanging counterpoise on
the bridge itself is dispensed with. The bridge also is lighter, cheaper,
and more easily worked, it also exposes less surface to a wind.
What I claim is the construction of counterbalanced lifting bridges
with separate counterweight applied, substantially as described.
In witness whereof, I, the said Walter Raleigh Browne, have here-
unto set my hand and seal, this Thirteenth day of November,
in the year of our Lord One thousand eight hundred and seventy-
three.