CERTAIN IMPROVEMENTS IN THE APPARATUS OR MA- CHINERY TO BE EMPLOYED AS CENTERINGS OR SUPPORTERS IN THE CONSTRUCTION OF BRIDGES AND ARCHES, AND IN TUNNELS OR OTHER MINING OPERATIONS
Year: 1838

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOSEPH
FRASER; of Halifax, Railway Contractor, send grecting.
WHEREAS I did by petition humbly represent unto Her present most
Excellent Majesty Queen Victoria, that after considerable application and
expense I had invented "CERTAIN IMPROVEMENTS IN THE APPARATUS OR MA-
CHINERY TO BE EMPLOYED AS CENTERINGS OR SUPPORTERS IN THE CONSTRUCTION OF
BRIDGES AND ARCHES, AND IN TUNNELS OR OTHER MINING OPERATIONS;" and Her
said Majesty, being willing to give encouragement to all arts and inventions
which may be for the public good, was graciously pleased, by Her Royal
Letters Patent under the Great Seal of the United Kingdom of Great Britain
and Ireland, bearing date at Westminster, the Third day of November, One
thousand eight hundred and thirty-eight, in the second year of Her reign, for
Herself, Her heirs and successors, to give and grant unto me, the said Joseph
Fraser, my exors, adiñors, and assigns, Her especial licence, full power, sole
privilege and authority, that I or they, by myself or themselves, or by my or
their deputies, servants, or agents, or such others as I or they should agree
with, and no others, during the term of fourteen years from the date of the
said Letters Patent, should and lawfully might make, use, exercise, and vend
my said Invention within that part of Her said Majesty's Dominions called
England; Her Dominion of Wales, and Town of Berwick-upon-Tweed, in
such manner as to me, my exors, admňors, and assigns, shall seem meet, and
as that I or they shall enjoy the whole profit and advantage arising by reason
A

page_text: of the said Invention during the said term of fourteen years, and for that end
Her said Majesty requires and strictly commands all Her subjects whatsoever,
within England, Wales, and Berwick-upon-Tweed as aforesaid, that they shall
not, neither directly nor indirectly, make, use, or put in practice my said Inven-
tion, or any part thereof, nor in any wise counterfeit, imitate, or resemble the
same, nor make any addition thereto or subtraction therefrom, whereby to
pretend himself or themselves to be the inventor or inventors thereof; and
whereas the said Letters Patent contain a proviso, obliging me, the said
Joseph Fraser, particularly to describe and ascertain the nature of my said
Invention, and in what manner the same is to be performed, by an instrument
in writing under my hand and seal, and to cause the same to be inrolled in Her
Majesty's High Court of Chancery within six calendar months next and
immediately after the date of the said 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
Joseph Fraser, do hereby declare that my said Invention is described and
ascertained in manner following, and by the aid of the Drawing hereunto
annexed, that is to say:-
My said improvements in the apparatus or machinery to be employed as
centerings or supporters in the construction of bridges and arches, and in
tunnels or other mining operations, consist in arranging such centerings or
supporters in manner herein-after particularly described, so that the same may
be readily advanced forwards a certain distance or length at a time, in a
direction that the construction or building of the bridge, arch, or tunnel is
progressing, by continuation of one such length at the end of another, but
leaving that part or length thereof which has been last constructed or built
still supported by those laggings or planks on which the same was built, that
support being kept up until the centerings or supporters have been advanced
another length forwards, so as to be ready to receive and sustain all the said
laggings or planks which are then advanced endways forwards, but only a few
at a time, merely as fast as they are wanted for sustaining the new length of the
bridge, arch, or tunnel that is going to be constructed or built in continuation
of the preceding length, and those laggings or planks which are not at the
time so wanted remain in their original position for sustaining the building of
the preceding length which was last made upon them, until they in their turns
are wanted, one after another, for sustaining their respective portions of the
new length that is going to be constructed or built upon them in their new or
advanced position; and for the purpose of readily advancing the centerings or
supporters forwards a length at a time, I make that one center or support

page_text: which is the most advanced of all the others in the form of an arch or bow,
whereof the interior or concave edge conforms nearly (as to curvature and
dimensions) with the intended inside of the bridge, arch, or tunnel which is to
be constructed or built; and the said arch or bow is made without any interior
cross ties, struts, braces, or other framing, (unless temporary, which can be
easily removed,) in order that it may not encroach in any considerable degree
upon that space which is to become the interior of the bridge, arch, or tunnel
when finished, but the requisite substance of the said arch or bow, which
thus forms the most advanced center or support, occupies the space where
the brickwork or masonry of the bridge, arch, or tunnel is to be constructed
or built, that brickwork or masonry being laid upon the laggings or planks
which are applied with their most advanced or foremost ends abutting
endways against the said most advanced centre or support, and deriving
their own support therefrom by resting upon a prominent ledge or border
of metal which projects out from the hindmost face or vertical surface of the
said most advanced centre or support, in conformity with the interior or
concave edge of the said centre or support; wherefore the said interior or
concave edge of that most advanced centre or support is only so much less
than the intended inside of the bridge, arch, or tunnel as the thickness of the
said laggings, together with that of the said prominent ledge of metal. The
said most advanced centre or support is sustained with its two ends or abut-
ments standing upon the brickwork, masonry, or rock, which constitutes the
side walls or piers of the bridge, arch, or tunnel, or upon suitable props or
supporters, and, as above explained, its projecting ledge affords the requisite
support for the foremost ends of the laggings without filling up or occuping
the interior space within those ends of the laggings; but the other centres or.
supports which are to sustain the same laggings, near to their hindmost ends,
and at their mid-length, must be of a smaller size so as to apply their convex
or exterior circumferences to the laggings, in order that the latter may rest
upon and be sustained thereby in due place; and the said two smaller centres or
supports are sustained on legs from any suitable floor or horizontal bearer beams
at or above the bottom of the bridge, arch, or tunnel, but within the interior
thereof; and the said two centres or supports are erected upon and united
together by horizontal beams, so as to constitute one frame, which, when
lowered a little, is capable of moving horizontally along in the lengthways of
the tunnel, and thereby travelling with the said centres, both together, like one,
by means of trucks or rollers at the feet or lower ends of their several legs
running along the said floor or horizontal bearer beams, and in so moving or
travelling the said two centres, or supports (having been lowered along along with

page_text: the said frame, and thereby let down so far as to quit contact with the laggings,
will pass through or beneath the interiors of those laggings, and the foremost
of those two, or the middlemost of the three centres or supports, will pass
through or beneath the interior of the foremost or most advanced centre or
support, which, as befere mentioned, sustains the foremost ends of all the said
laggings by means of its prominent lodge or border, as aforesaid. But note.-
Whilst the said two centres or supports are so moving forwards, the hindmost
ends of the same laggings are kept up in due place by a temporary slight
centre or support, which may be a half hoop of metal, sustained by suitable
prominences or brackets from the side walls, or on the upper ends of props
from below, and bearing up closely beneath or within all the laggings, so as to
support their hindmost ends, whilst the aforesaid two centres or supports are
let down, as before mentioned, so far as to quit contact with the laggings, in
preparation for those two centres or supports travelling or advancing forwards;
and when the hindmost of the said two centres or supports has by that
travelling or advancing forwards arrived nearly up to what has been hitherto
called the foremost or most advanced centre or support, and which still sustains
the foremost ends of all the laggings, then, by raising up the moveable frame
and legs on blocks, wedges, or screws, the hindmost of the centres or supports
may be raised so much as to place the same again in contact with or beneath
the laggings, and thereby their foremost ends will become supported without
further dependence on what has been called the foremost centre or support;
and for the purpose of so bearing up firmly beneath all the said foremost ends
of the laggings as that they will have no further dependence, as aforesaid, the
said hindmost of the centres or supports is provided with a series of setting
screws or wedges, to be forced up into very close contact beneath or within
the several laggings; and then what has been called the foremost centre or
support may be let down so much as to drop its prominent ledge clear away
from those foremost ends of all the laggings which it has hitherto supported,
leaving those ends firmly supported by the setting screws or wedges of the of
the said hindmost centre or support, and then the foremost centre or support,
being no longer necessary in the position it has hitherto occupied, is moved or
advanced forwards as much as is requisite for constructing or building the
next length of the bridge, arch, or tunnel, which length is to be constructed
or built at the end of or in continuation of that length thereof which has
been recently finished, and which still remains supported by the same laggings.
whercon it was built; and in so advancing or moving forwards the said
foremost centre or support, the same will pass over the middlemost of the
three centres or supports, which latter has for the present got in advance, in

page_text: consequence of having been recently passed under the foremost centre or
support when the moveable frame travelled or advanced forwards, as already.
mentioned; but when the foremost centre or support is also advanced or:
moved forwards in its turn over the middlemost one, that foremost one will
regain the advance and be in its proper position of foremost centre or support,
and is to be there set up firmly and truly in the intended line of the bridge,
arch, or tunnel in a vertical position, with its ends or feet resting on the newly
built or the rocky side walls of the bridge, arch, or tunnel, with such props or
supporters thereto as may be required. And in order to facilitate the placing
and fixing of the said foremost centre or support in the exact position that it
ought to have, its said ends or feet may have sole plates of wood or iron to
rest on the newly built or rocky side walls, with setting screws or wedges to
adjust the position of those ends or feet on the said sole plates; and also
the middlemost centre or support before mentioned must be adjusted on
its frame before mentioned, so as to stand truly in the intended line of the
bridge, arch, or tunnel, that is to say, to stand exactly in line between the
foremost centre or support, which has been recently advanced forwards and
fixed, and the hindmost centre or support, which, as before explained, has
been previously fixed beneath or within the foremost ends of the laggings, and
which is still supporting those ends by its setting screws or wedges. And now
the centres or supports being ready for beginning to construct or build another
length of the bridge, arch, or tunnel, one or a few of the lowermost laggings
at each side or springing of the arch are set free by releasing those particular
setting screws or wedges of the series of screws or wedges in the hindmost
centre or support which sustained the said few laggings, but without disturbing
the screws or wedges of any other of the laggings; and, in the like manner,
the hindmost ends of the same few laggings are set free from the temporary
centre or support by which, as before mentioned, they have been and still are
upheld, and the few laggings which are so set free are then moved endways
along until their foremost ends abut against the foremost centre or support,
and become lodged in due place upon the projecting ledge of that centre or
support, so as to be firmly sustained thereby; the hindmost ends of those same
laggings being at the same time sustained by those setting screws or wedges
of the hindmost centre or support which did previously sustain the foremost
ends of the same laggings, and which screws or wedges were released or
unscrewed as before mentioned, so as to set those foremost ends free, in order
that the said laggings might be moved forwards endways; but that being
done, the same setting screws or wedges are then screwed up again so much
as to hold the said hindmost ends of the laggings up into close contact with

page_text: the finished brickwork or masonry.
The mid-length of the laggings rest
against the middlemost centre or support, and then the constructing or
building of the new length of the bridge, arch, or tunnel is commenced at
the springing of the arch at each side thereof, upon or behind the said few
laggings which have been so brought forwards, as aforesaid; and when so
much is completed as those laggings have to support, and other laggings are
wanted higher up the arch, then a few more are in turn brought forwards, in
the same manner as above described; and when as much more of the building
as they have to support is completed, then a few more laggings are in turn
brought forwards, and so on until the arch is completed up to the crown,
where the two sides meet each other and may be joined, or the arch closed or
keyed in after the usual manner. Wherefore, by means of my improvements,
the centerings or supporters are very readily moved forwards or advanced
forwards a length at a time, leaving all the laggings undisturbed, in order that
they may continue to support so much of the bridge, arch, or tunnel as has
been constructed or built upon them, until the time when some of the same
laggings are wanted for supporting their share of the new length of the
bridge, arch, or tunnel, and then (but not before) a few (but only a few) of
the laggings are advanced endways forwards, still leaving the rest undisturbed
until they are wanted in their respective turns, so that the laggings are always
kept fully employed in their office of supporting the brickwork or masonry, for
they are not removed from the support of the recently finished work until the
moment when they (or a few of them) are required to support their part of
new work which is in progress of construction.
And for the more complete explanation of my said improvements, I have
hereunto annexed a Drawing, wherein Figure 1 is a front view of the
centerings or supporters, with some of the laggings as they appear when
in use in the arch of a tunnel, and part of the brickwork which is supported
by the laggings is also shewn. The eye of the spectator is supposed to be
nearly in the middle of the tunnel, and nearly at the level of the springing
of its arch, and to be looking forwards in the direction in which the con-
struction of the tunnel is progressing. The Figure.represents the centerings
or supports when they have been recently advanced forwards, in prepara-
tion for the construction of a new length of. the tunnel, which length is
supposed to be in progress, but which is only just begun; that preceding
length thereof which has been already completed not being represented, or
only a very small portion of the brickwork thereof, and a portion of the
laggings at one side of the arch being represented as having been already
advanced endways forwards for the support of so much of the new building of

page_text: the arch as they are appointed to support. And note.-The same or nearly
the same number of laggings would in reality also appear at the other side,"
because the building of the arch is carried on at both sides at the same time;
but the laggings at one side are omitted in Figure 1, in order to shew the
foremost centre or support more clearly.
Figure 2 is vertical and longitudinal section of the arch of the tunnel,
shewing all the centres or supports, and all the laggings, when they are in their
proper places for sustaining a length of the arch of the tunnel which has first
been completed; but this Figure represents the state of the parts just before
beginning to advance the centres or supports forwards, in preparation for con-
structing another length at the end of (and in continuation of) that which has
been recently completed, and which is represented by the Figure.
Figure 3 is another vertical and longitudinal section of the arch of the
tunnel, corresponding to Figure 2, but shewing the centres or supports just
after they have been advanced forwards from their previous position, Figure 2,
in preparation for commencing a new length of the arch of the tunnel, the con-
struction or building of which is only just begun behind the two lowermost of
the laggings, which are represented as having been advanced forwards, all the
other laggings remaining just as they were, and as they appear in Figure 2,
and continuing to uphold to newly finished brickwork or masonry; Figure 3
therefore represents nearly the same state of the several parts as Figure 1.
The same letters and numeral characters are used to denote the same or
corresponding parts in all the three Figures.
A is the foremost centre or support; B the middlemost, and D the hind-
most centre or support. C, Figures 2 and 3, is the temporary slight centre or
support for holding up the hindmost ends of the laggings when the middlemost
and hindmost centres B, D, are to be advanced forwards, and the laggings are
to be left behind undisturbed, as before mentioned. The foremost centre A is
stepped or supported on the newly built or rocky side walls of the tunnel, with
such props or supports thereto as may be requisite; and the hindmost temporary
slight centre C is also supported by projecting pieces from the finished side
walls. The middlemost and hindmost centres B, D, are both supported on a
travelling frame, consisting of horizontal longitudinal beams E, E, at each
side united by horizontal cross beams F, F, to form a floor or platform,
which is sustained upon upright and oblique legs G, G, with trucks a, a, at
their lower ends to run horizontally upon longitudinal bearer beams or rails
H, H, which are laid either on the floor or bottom of the tunnel, as repre-
sented in the Figures, or else they may be laid alongside of the side walls,
at any suitable height up the same, being in that case supported upon

page_text: temporary cross beams laid across the opening of the tunnel from side wall to
side wall, or from each side wall to a solid, which may, in some cases, be left
unexcavated in the middle part of the opening of the tunnel until after
the building is finished, or by temporary stones, beams, or brackets left pro-
jecting for the purpose out from the side walls, or by upright props placed
against the side walls; or by any other means, so as that the said horizontal
longitudinal bearer beams may be firmly supported, suitably for the trucks or
wheels a,
to run forwards along them. The foremost centre or support A
may be made of strong timber, in pieces or thicknesses, well united and
secured at their junctions by iron bolts, its concave or inner edge being of a
corresponding or parallel curve to the concave or inside of the arch of the
tunnel, and only so much less in dimensions than that inside as the thickness
of the foremost ends of the laggings, in order that the exterior surfaces of the
laggings, when they are in place, may be exactly the proper form and size for
the interior of the arch of the tunnel; and the said concave or interior edge of
the foremost centre or support A is lined with a strong band or hoop of metal e,
which forms a continuous curve of metal, in pieces well joined by revits or
screws, metal to metal, all the length of the curve, and which is firmly bolted
to the wood to strengthen it, and which projects backwards sufficiently beyond
the hindmost vertical face of the centre or support A to afford a secure
lodgment for the foremost ends of all the several laggings L, L. Note.-In
Figure 1, the foremost centre A is represented twice, that is to say, it is
supposed to be seen in outline at Z, near to the eye, which is the position
that it had before it was advanced forwards; but the said representation
in outline is only imaginary; the real position of the foremost centre in
Figure 1 is that seen at a distance, and marked A, where it appears to be sup-
porting the foremost ends of the laggings L, L, at one side of the arch. The
lower ends of the foremost centre or support A are strengthened with metal,
having holes therein to receive vertical setting screws, such as is shewn at 6 in
the imaginary view, Figure 1, and horizontal setting screws d, for the purpose
of adjusting the said foremost centre A into its true intended position in the
line of the tunnel. The vertical screws 6 form feet, which sustain the weight of
the foremost centre A, those feet resting upon sole plates of wood or metal,
which are laid upon the side walls from which the arch is to spring; and if the
brickwork or masonry of those walls (from being newly built) is not so firm as
is desirable, the said sole plates may be propped and supported in any suitable
manner; the horizontal setting screws d act laterally against the earth
or rock which has been excavated. The said setting screws b, d, may have
square shanks fitted into corresponding holes in the lower ends of the centre or

page_text: support A, and the threaded parts of the screws may have square nuts, which
are lodged in mortice holes cut into those lower ends, and which nuts being
turned by a wrench will set the shanks of the screws further out or in, so as to
adjust the position of the centre or support A according to suitable lines and
marks, as is usual in setting centerings; and when its exact position is attained,
then blocks or wedges are inserted between the lower.ends and the said sole
plates, in order to sustain it firmly; or the requisite adjustment might be
attained by means of such wedges, without setting screws. The breadth and
thickness of wood used for the foremost centre A may be according to the
strength required; it may be as much as the breadth of the brickwork or
masonry of the arch that is to be constructed. Note. -The foremost centre A
stands opposite to the end of the newly built brickwork or masonry of the arch
of the tunnel, which end must be left, as is usually done, with prominent
bricks, called toothing, for joining to the next length of the arch, so that the
centre A covers and protects the said end toothing from accidents to which it is
otherwise liable by the falling of masses from the upper part of the face of the
excavation, and still more in cases of rock, which must be removed by blasting
with gunpowder; fragments of the rock are frequently projected with great
violence against the end of the newly erected brickwork, doing injury of the
toothing, and shaking the joints of the brickwork before they are firmly set;
also such fragments frequently strike so violently against the interior framing,
braces, or tye beams of the centering commonly used, as to loosen or throw
down the newly formed brickwork, which is at the time dependant upon the
centerings and laggings for its support. But on my plan the foremost centre A
being an open arch without any ties, braces, or internal framing, far less liable
to be struck by any such fragments, and being opposite to the end toothing of
the newly built brickwork, it protects the same so effectually that when any
fragment does not strike the foremost centre A, it can scarcely do injury,
whereas the same fragment would in the common plan strike the end of the
brickwork, and do mischief. But note. Although the foremost centre A is
represented as an open arch without any cross tie or chord, and although it is
desirable that it should be so, nevertheless it may have any suitable chord and
ties and braces stretched across it to give it strength, provided that they are
fixed to the arch A, with bolts or hooks, or joint pins, so as to be easily
removeable in order to render it an open arch at the time when it is to
be advanced forwards. It is very convenient to the workmen to have the
foremost centre an open arch quite out of their way, but over head, in the
space which is to be afterwards occupied by brickwork, leaving nearly all
the interior of the tunnel free from cross braces, as appears in Figure 1, or if

page_text: any, only a few, and those of small size. The upper or exterior curve of the
front centre A is covered with a continuous curve of metal, bolted through
the wood with the same bolts which fasten the interior curve of metal e, before
mentioned, and there is also a continuous curve of metal, covering and bolted
to the whole of the front face of the centre A. The middlemost and
hindmost centres B and D are most conveniently made of iron, and
like open arches, but with horizontal chords or tie beams across them to
give strength; but that openness, although desirable to gain room, is not
essential to my plan, for the centres B and D may be of wood, with any
suitable kind of internal framing. The hindmost centre D is represented
as being made of cast iron, with a series of setting screws f passing through it
in radiating directions at equal distances apart, with one such screw f for each
of the laggings L. The screws f.f, may be fitted with their threaded parts to
screw into wrought-iron nuts, let into suitable square holes in the cast iron, in
which case the screws must be turned round by applying a key or winch
to squares at the inner ends of the screws and plugs x, x, with square stems
being fitted into the aforesaid square holes may be forced outwards therefrom
by action of the screws, and each such plug having a broad flat head, the same
applies behind one of the laggings L, so that by screwing the screws f, f, the
several laggings L, L, can be urged up into very close contact with the brick-
work or masonry. The cast-iron centering, Figure D, may be cast in two
pieces, united by screw bolts through a flange joint at the crown of the arch.
The feet or ends of the iron centering D are fixed by screw bolts on the
timber frame E, E, F, F, which may be strengthened by an iron tye bolt h,
Figure 1, that will keep up the horizontal cross beam F from bending down
by its weight. The middlemost centre B may be cast iron, of the same
pattern as D, but it does not require setting screws, or it may be made of
wrought iron, and it is fastened with its feet on the same wood frame E, E, as
the bindmost centre D. The two centres B and D are united by horizontal
iron bars k, k, extending in the direction of the length of the tunnel from one
of those centres to the other, in order to hold both in their respective vertical
planes, and at a suitable distance apart. The timber frame E, E, is supported
on its upright and oblique legs G, G, which stand up from horizontal longi-
tudinal beams T, T, that have the trucks a, a, beneath them; that is, in
cases when the support for the centres is to be derived from the bottom or
floor of the tunnel; but when the excavation is made in rock, which will stand
of itself to form side walls, then only the upper part for the arch requires to be
excavated at first, leaving the lower part unexcavated until after the arch is
finished, in which case there need be no legs G, G, but the trucks a, a, will be

page_text: applied to the beams E, E, as at j, j, Figures 2 and 3, and the bearer beams
or rails II, II, will be laid just beneath those beams E, E; and also in some
other cases the said bearer beams or rails H, H, may be fixed alongside of
each of the side walls of the tunnel, and supported by cross beams or brackets
or props, as before mentioned, at such a height as to support the frame E, E;
without legs G, G, or with only short legs; but in either case the trucks a, a,
are only for use when the centres B, D, are to be advanced forwards; but when
these centres are to be fixed in place for supporting the laggings L, L, then
the beams E, E, or else the beams T, T, at the bottom of the legs G, G, (if
such beams and legs are used.) must be raised on blocks and wedges 1, 1,
applied beneath the beams E, E, or T, T, just under the ends of the centres
B and D, or beneath. the lower ends of the legs G, G, as the case may be, so
as to raise up the centre B into the exact place that it is required to have
in the line of the arch. For note. When the two centres B, D, and their
moveable frame E, E, F, F, G, G, T, T, is resting on the trucks a, a, then
those centres will be let down a little below their proper places, so that they
will quit contact with the laggings L, L, which they have previously supported,
and so that by moving the whole frame forwards on its trucks a, a, the two
centres B, D, can be passed through or beneath the open arch of the foremost
centre A without touching the same, and it is by such moving forwards on the
trucks a, a, that the two centres B and D, with their framing E, E, F, F,
after being let down to rest on those trucks, become advanced from the position
shewn in Figure 2 to the position shewn in Figure 3, with the hindmost
centre D advanced quite close up to the projecting ledge e of the foremost
centre A, and then the frame E, F, G, T, is blocked and wedged up at 1, 1;
Figure 3, so as to raise up and bring the two centres B and D as nearly as can
be into their proper places in the line of the intended arch. The frame
E, E, F, F, being thus made firm in its new or advanced position, Figure 3,
the several setting screws f,f, of the hindmost centre D (which screws f may
require in some cases to have been screwed back before beginning to advance
the centres B, D, from their position, Figure 2), are screwed up into very
close contact with the foremost ends of all the laggings L, L, so as to take the
weight of and sustain all those foremost ends without any further dependance
on the projecting ledge e of the front. centre A, which has hitherto supported
those ends, but which centre A is not now required. to remain any longer in its
previous position, (which is that shewn in Figure 2, or by the dotted lines
Z in Figure 3); therefore the front centre A is let loose by removing
the blocks or wedges from beneath its two ends, and by regulating its
vertical setting screws 6 and its horizontal ones d, and so that its projecting

page_text: ledge e will quit contact with the foremost ends of all the laggings L, L,
in order that it may be withdrawn from those ends, leaving them firmly
supported by the hindmost centre D, without any alteration of their position,
and the foremost centre A being thus set loose is ready to be advanced
or carried forwards from its previous position (as dotted at Z, Figure 3)
to its proper advanced position A, Figure 3; and in order to effect such
removal or advance of the centre A with facility, a wooden bearer, faced
with iron, is fixed beneath it, so that the centre A becomes suspended by
its vertex resting across that bearer, in which state the whole weight of the
centre A being sustained, it can be easily slided forwards along the said bearer
into its advanced position, and in so advancing forwards the centre A will pass
over the middlemost centre B without touching the same. The said bearer for
the removal of the foremost centre. A is made in two lengths, whereof one is
applied with one of its ends resting upon the vertex of the hindmost centre D
(when the same is in the position shewn in Figure 3), and the other end of
the same length of the bearer rests upon the vertex of the middlemost centre
B, wherefore that hindmost length or portion of the bearer will be slightly
inclined, so that the centre A will become raised upwards by degrees as it is
advanced along the said bearer, in order to enable the centre A to pass clear
over the middlemost centre B without touching the same. The other or
foremost length of the same bearer, which forms a continuation of the first-
mentioned or hindmost length, rests with one end on the centre B, and with
its other or foremost end on any suitable prop or support on the unexcavated
ground or rock at the end of the tunnel; the second or foremost length of
the bearer is securely jointed to the first or hindmost length by suitable over-
lapping and cross pinning of the iron with which the upper sides of both
bearers are faced. The said foremost length is laid with a slight inclination
downwards, in order that the centre A may descend a little by degrees as it
advances forwards, so as to get down to its proper level by the time it has
advanced as far as its proper position A, Figure 3. The said advancing
motion of the foremost centre A along its said bearers may be given by a rope
or chain, fastened to the vertex of the centre A, close to the place whereby its
rests on the iron face of the bearer, and after being extended all along the
upper side of the bearer, the said rope may pass over a pulley at the end
thereof, and hang down or pass backwards into a convenient direction for men
to haul at the end; or what will be still more convenient is a small wind-up
roller, which may be applied at the foremost end of the bearer, to wind up
the rope or chain when the roller is turned round by a handle or handles by
a man or men standing in a suitable small excavation, which may be made in

page_text: the earth or rock at the end, or in further advance of the large or full size
excavation which has been already made, and within which a new length of
the tunnel is about to be constructed or built on the centering, as represented
in Figure 3. And note.-The said walls of the tunnel from which that arched
top is to spring will in most cases have been built whilst the centering was in
the position, Figure 2, before the advance or removal into the situation,
Figure 3, took place, or at any rate before the foremost centre A is advanced
forwards, as above described, because the two ends or feet of the centre are to
be set up on the most advanced ends of those side walls when the said centre
is fixed in its most advanced position A, Figure 3; and those most advanced
ends being newly built should be suitably propped or shored for enabling them
to sustain the said feet securely, and the last portion of the brickwork may be
laid with cement, or a large stone may be inserted at that most advanced end,
or a sole plate of iron may be laid on the brickwork, or a long stone or bar of
iron or beam of timber may be laid back into an excavation in the earth or
rock, and firmly bedded therein, with its end laying across the side wall to
form a sole plate for the feet of the foremost centre A to rest securely upon.
And note. Whilst the foremost centre A is in the act of being advanced
forwards upon its bearer, as above described, its two ends or feet will advance
along over the upper edges of the two newly built side walls, although without
touching them, but by laying a plank along each of those edges men may
walk thereon to assist in lifting and advancing the centre A forwards by
strength of their hands, or by assistance of levers, or rollers and planks, if
requisite, and by such means the centre A can be very easily advanced, how-
ever strong and heavy it may be. And note.-In case it is judged necessary
for strength to bave a chord or horizontal tye across the arch of the foremost
centre A, with a perpendicular tye or tyes thereto, the same may consist of two
sets of iron bars or rods, parallel one to the other, one such tye or set of tycs
being applied in a plane somewhat in advance of the foremost vertical face or
surface of the centre a, and the other in a different plane somewhat behind the
hindmost vertical face thereof, in order that the two tyes or sets of tyes may
be sufficiently apart to admit the whole breadth of the middlemost centre B
in the space between them without touching either, and in such case both
the said tyes or sets of tyes will concur in giving strength to the centre A
whilst the building of the arch is going on and loading weight upon it, but
after that, when the centres B, D, are in the act of being advanced from the
position, Figure 2, to the position, Figure 3, and have been advanced so far
that the middlemost centre B is arrived at the hindmost of the said two tyes
or sets of tyes which cross the opening of the centre A, then that hindmost

page_text: tie or set of tyes may be removed without disturbing the other or foremost tye
or set of tyes, and the centre B being advanced a little farther so as to come
up to the foremost tie or set of ties, then the said hindmost tie may be replaced
behind the centre B, and drawn tight by its screws, so as to give strength to
the centre A, whilst the foremost tie or set of ties is removed; in order to allow
the middlemost centre B to be advanced forwards in to its intended position,
Figure 3; by this means the foremost centre A may, if required, be kept
tied across without occasioning any difficulty in passing the middlemost centre
B beneath it. The ends of such ties should be applied to the centre A by
means of hooks or joint pins or tie heads, let into corresponding cavities, or
by cross keys or nuts and screws, or by any other mode commonly used in like
cases, by which the several ends of the ties can be very readily detached, in
order.to remove them, as above described, and then to replace them again; and
the ties must be provided with nuts and screws, by which they can be drawn
tight to retain the centre A in form. And note.-The middlemost centre B
may be taken to pieces, or it may be turned down from its vertical position,
so as to lay flatway upon the platform E, E, F, F, in order to pass it in that
state beneath the cross braces or internal framing of the foremost centre A,
if it is thought desirable to have any such cross braces or internal framing
thereto; and in such case, after the hiudmost centre D has been applied, as
before described, beneath the foremost ends of all the laggings L, L, and also
after the foremost centre A has been advanced forwards to the position,
Figure 3, which (if the middlemost centre B is taken in pieces or turned
down flat, as aforesaid) can be done without removing any of the ties, braces,
or internal framing that there may be across the foremost centre A, then the
said middlemost centre B may be put together again, or may be turned up
into its vertical plane, and fixed therein, so as to bring all the parts into the
situation represented in Figure 3; but although by the above means the
foremost centre A may have ties, braces, or internal framing (if required
for strength), nevertheless it is highly advantageous to dispense with all such,
and to use mere rings for centres, as is shewn in the several Figures, because
the whole of their interior is then left clear space for the workman, and their
operations will be greatly facilitated, in consequence of having more room
than there could be if the rings had internal ties or framing within them. The
slight temporary centre C, Figures 2 and 3, which is for sustaining the hind-
most ends of all the laggings L, L, must be fixed up in its place, as shewn in
Figure 2, before the centres are begun to be advanced forwards to their
position, Figure 3, in order that the said temporary centres C may sustain the
-hindmost ends of all the laggings, independently of the centres B, D, before

page_text: the same are removed. The center C is a flat and flexible hoop of wrought
iron, which is applied within all the laggings, its two ends being supported
upon the projecting ends of two pieces of wood m, which are fixed into holes
in the side walls, so as to project out therefrom. The feet at the lower ends of
the centre C may have upright screws n tapped into them, and those screws
standing upon the said supports m, admit of forcing up the centre C nearly
into contact with the hinder ends of the laggings L, L, and all those ends are
slightly tapered in breadth near to their extremities, in order to leave spaces
between them, into which wooden wedges p, p, can be inserted, as seen in
Figures 2 and 3; and those wedges being broader than the thickness of the
laggings will jamb fast between the finished brick work or masonry of the arch
and the centre C, and will thereby hold off the said centre C so far from the
said brickwork or masonry as to leave the end of the laggings quite unconfined
in the
space between the centre C and the brickwork or masonry; but as the
several wedges p, p, become fixed by jambing in the said space, they serve to
keep the several laggings L, L, in due place, one in respect to another, so that
when the several blocks and wedges 1, 1, are withdrawn from under the
framing E, E, F, F, G, G, T, T, and the same is let down to rest on its trucks
a, a, whereby the two centres D and B are let down so much as to quit con-
tact with all the laggings L, L, in order that those centres may be removed or
advanced forwards into the position represented in Figure 3, then the laggings
L, L, will be left supported at their hindmost ends (as is there represented) by
the several wedges p, p, of the centre C, and by the several setting screws.f, f,
of the centre D, at their foremost ends; wherefore, after all the parts have been
brought into the position, Figure 3, ready for commencing the construction or
building of another length of the arch for the tunnel, the lowermost setting
screws f, f, of the centre D being screwed back, will release the foremost ends
of the lowermost or the two lowermost laggings L,.L, leaving the same at
liberty to be advanced forwards endways the workmen, their hinder ends
drawing out from between the centre C and the finished brickwork or masonry
of the arch, and leaving all the other laggings L, L, retained in due order by
the several wedges p, p, of the centre C. And note.-In lieu of such wedges
p,p, a series of screw pins might be tapped through holes in the centre C, so
as to pass through the spaces left between the hinder ends of the several
laggings L, L, (where the wedges would be inserted,) and the ends of those
screws pressing against the finished brickwork or masonry of the arch would
perform the same office as the wedges p,p; and when the lowermost or the
two lowermost laggings L, L, at each side have been advanced endways for-
wards, as shewn in Figure 3, so that their foremost. ends become securely

page_text: lodged on the projecting ledge e of the foremost centre A, then the hindmost
ends of the said laggings are forced, by their respective setting screws f. f, of
the hindmost centre D, into very close contact with the finished brickwork
or masonry of the arch, and after that is done, the building for the springing
of the arch may be begun upon the top of each side wall, behind the said
lagging or laggings; and when the building has been carried up as high as that
lagging or those two laggings extend, and after all space between the exterior
of so much of the building and the excavated ground has been filled up solid,
then one or two laggings next above the former are advanced forwards and
fixed in like manner; and the building behind them being completed, one or two
more are in turn advanced forwards, and so on, until the whole of the laggings
have been brought forwards, and until the arch has been built up thereon from
both side walls to meet at the crown, where the two sides are to join together.
And note. In order to ensure that the several courses of brickwork of which
the arch is to be composed shall be truly laid in a horizontal and longitudinal
direction, prominent pieces of wood are fastened to the hinder vertical face of
the foremost centre A, as represented at z, Figure 1, in order to receive the
alternate courses of bricks between them, so as to form a true pattern for the
toothing that is intended to be left at the foremost end of that length of arch
which is now about to be built. Those bricks which are to form the promi-
nences of the said toothing are laid with their ends in the spaces between the
said prominent pattern pieces z, and those intervening bricks which are to be
at the hollows of the toothing are laid with their en:ls against those prominent
pattern pieces. And whereas the toothing left at the foremost end of the last
length of arch which has been finished, as shewn in Figure 2, has been previously
built in the same manner, by the same pattern pieces z for their pattern, that
finished toothing will truly correspond with what is now about to be built
from the same pattern pieces z; wherefore the several courses of brickwork
being laid straight from the said finished toothing to the new toothing which
will be formed by the said pattern pieces z, those courses will range truly in
their intended horizontal longitudinal direction, so that the brickwork of the
two sides, when they meet at the top or crown, will be truly parallel one to
the other, ready for closing or keying in the arch. And note.-If the arch
is to be built in stonework masonry, then the said prominent pattern pieces
must be suitably arranged against the hindmost vertical face of the foremost
centre A, to form the pattern of the courses in which the masonry is to be
laid, for in all cases, whether for brick or for stone, the whole series of the
said pattern pieces a must form the true pattern of those courses, and, if more
convenient, instead of projecting pattern picces, the places they occupy may

page_text: be indicated by deep lines cut into the hindmost face of the foremost centré A,
to serve as pattern marks to lay the courses by. The proper place for the
hindmost end of each course being thus fixed by the finished toothing to which
that course is to join in continuation, and the proper place for the foremost end
of the same course being also fixed by the said pattern pieces z (or by the
pattern marks in lieu thereof), the lagging or laggings L, which is or are
advanced forwards, will extend straight from one of those ends of the course.or
courses to the other end, so as to serve as straight edges for the building.
thereof truly, without winding, or twist, or crookedness. And note.-In order
to ensure the true placing of the several laggings without any care for so doing,
the projection ledge e of the formost centre A may have a series of bolt holes
through it, with one such hole at the proper place for the mid breadth of each
lagging, and the foremost end of each lagging having a little hole through
it, a small screw may be put up through the hole in the ledge e, to screw
into the said hole in the end of the lagging, which end may be bound or
plated with iron to receive the screw. By this means the true place for the
foremost end of each lagging will be determined, and also the foremost centre
A will be held firm in its vertical position, so that it cannot move away from
the foremost ends of the laggings, nor can they escape from their full intended
lodgment on the ledge e, when the building is finished, as in Figure 2. Those
screws must be withdrawn before the centre A can be advanced to the position
Figure 3; or, in place of such screws, steady pins may be fixed fast into the
ledge e, so as to stand up above that convex surface thereof whereon the ends.
of the laggings are to be lodged; and the end of each lagging may be cut with
an open notch or fork at its foremost end to fit over the said steady pin, which
pin need not in such case be withdrawn when the centre A is to be advanced
forwards, or small teeth of iron may be fixed to the said ledge e, to stand
out from the convex surface thereof across its breadth, and joining to the
vertical face of the centre A, with one such tooth at every place where there is
to be a junction between the foremost ends of two adjacent laggings, which
ends must be reduced sufficiently to enter into the spaces left between those.
teeth; the said spaces will form a series of cells for the reception of the fore-
most ends of the several laggings, each one in its true place, and admitting of
no deviation from that true place, and some of the laggings may have screws
screwed up through the ledge e into the ends of them, as before mentioned, in
order to hold the foremost centre A-firmly in its true vertical position. And
note. In case the slight temporary centre C is made, as herein-before men-
tioned, with a series of holes through it for the reception of screw pins, in lieu
of the wedges p, p, the places of the said holes must correspond to the said
R

page_text: teeth on the ledge e, by which it is divided into cells. If the slight centre C is
provided with a series of such holes, then such screw pins may be inserted at
some places between the hindermost ends of some of the laggings for retaining
them in their true places, whilst wedges p, p, are used for others of them. The
several centres A, B, D, may be made of wrought iron, the pieces thereof being
securely revitted one to the other, so as to form a continuous curve all the length
of the centre, and with that condition the iron may be combined with wood,
and of such strength as is suitable for the size and weight of the arch which
is to be constructed; and in all cases where that weight and size will permit, it
will be desirable to have the interior of the centres left open, as represented in
the Figures, in order to leave the workmen more room to carry on their opera-
tions. The scaffolding V, V, Figure 1, whereon the workmen are to stand
whilst building the arch, consists of planks laid parallel to the laggings upon
the cross beams F, F, which, as before mentioned, are trussed from bending
down by an iron tye h to each. The foremost ends of those planks are laid
upon a like cross or tye beam, which may be fixed temporarily across the fore-
most centre A for that purpose, with a vertical suspension bolt from the top of
the centre A, to keep up the middle of the said cross or tye beam; or in lieu of
such a cross beam, iron bearer bars W, W, Figure 1, may be applied upon
bolts fixed into and projecting horizontally from the foremost face of the fore-
most centre A, one end of each of those bearers being sustained on those bolts
as there centres of motion, and the other ends of the same bearers being
sustained by vertical chains w, w. These bars can, if required, be hauled up
by their chains w, w, so as to lay flat against the front face of the foremost
centre A, in order to keep them out of the way of fragments of stone which
may be thrown down from the face of the excavation, in cases where it is in
rock, which must be removed by blasting, for when the scaffold planks V, V,
are removed, and the bars W are hauled up, the whole interior space of the
foremost centre A is open to allow such fragments to fall down backwards.
And note. In ordinary cases of blasting, it may be expected that the cross
beams F, F, and legs G, G, of the frame E, E, will be far enough back to
avoid being struck by such fragments; but after a length of the arch has been
closed and keyed in, as in Figure 2, then, in case a very strong explosion is
about to be made, which it is expected might throw back fragments so far as
to do injury to the said framing, then its blocks and wedges 1, 1, may be with-
drawn to let it down on its trucks a, a, and to let down the centres B, D, from
contact with the laggings L, L, and then the said framing, with those said
centres, may be removed backwards far enough out of the way, the setting
screws f,f, of the hindmost centre D being first screwed back, in order to allow

page_text: that centre D to pass clear under or within the slight temporary centre C, and
after the explosion the framing may be advanced forwards again. As the
building of the arch proceeds upwards, and the workmen require the planks on.
which they stand to be fixed higher and higher, the same may be supporte:l
on horizontal cross ties, which can be stretched across each of the centres, as
shewn at y, y, Figure 1, at any suitable heights, where bolt holes are provided
in each centre for that purpose. The bolts, which serve as centre pins for the
iron bearer bars W, can be raised to various heights in that manner, and the
chains w, w, can be hooked up to suitable lengths. The work of excavation'
for the tunnel may be carried on as usual, but the open space left within the.
centres, as shewn in Figure 1, will facilitate the work, and the sloping props,
which are employed as usual to keep up the face of the excavation, as shewn
at R, R, Figure 2, can be applied and removed without impediment from the.
centres.
And whereas horizontal bars, such as S, Figure 3, are required to sustain
the roof of the excavation that is made to receive a new length of the arch.
until such time as that length is built, those bars S are placed as usual with
their hindmost ends bearing on the foremost end of the recently built brick-.
work or masonry of the last length that has been constructed, as is shewn in-
Figure 3. The foremost centre A enables the brickwork or masonry to sustain
the pressure of those bars S, and on my plan the hindmost centre D, being.
applied and screwed up tight beneath the foremost ends of the laggings, will
sustain the said foremost end of the brickwork or masonry effectually from.
being pressed down by the bars S when the centre A is removed and advanced
forwards, and when it is so advanced it can be placed very near against the
end of the excavation without any necessity for waiting until the whole of the:
upper part of that face is cut away nearly flat and vertical, as must be done.
when the interior of the foremost centre is filled up with an internal framing.
in the usual manner, for as soon as ever the part where the side walls and the.
arch are to be built are sufficiently excavated to give space for building them,
the side walls can be erected, and the centres set up on my plan, and the arch
built and finished before the central mass of the excavation is completed,
whereby the roof of the excavation is not left open so long a time as usual.
before the arch is constructed beneath it, that is, in cases where the lower part
or floor of the tunnel is in ground which does not require to be laid with an.
inverted arch before the side walls are built, and in cases where the exca-
vation is in rock, which will stand firm enough of itself to serve for side.
walls, or for part of the height thereof, the excavation will only require to be
made at first for receiving the arch and such part of the height of the si.le,
n O

page_text: walls as are to be built. In such case, my centering being open, without
internal framing, leaves room for the workman to make the requisite excavation
for the arched part without inconvenience or loss of time, and as soon as a
sufficient basis for commencing the arch can be obtained, either on the natural
rock, or on side walls built up a small height thereon; then the centering may
be set up, and being open, without internal framing, will leave room for the
workmen to carry on their operations for getting the arch constructed and
finished in a short time after making the excavation which it is to sustain,
leaving the further excavation of the rock for the lower part of the tunnel to
be performed afterwards, which can be done almost as easily as quarrying in
the
open air, because the arch of the tunnel is standing firm over head, with a
clear space above for air, and the excavating workmen are not obstructed by
props and timbering, or centering, or by building operations. The excavating
is thus divided into two operations, whereof one, for the upper part of the
tunnel, must be done before the constructing of the arch, but the other, for the
lower part of the tunnel, is done afterwards under cover of the arch which has
been completed. My plan of centering being open, without internal framing,
is well adapted for proceeding in that manner when the nature of the rock will
permit, and the moving frame or platform E, E, F, F, being without legs
G, G, or only short ones, is lighter, and can be more easily moved in order to
advance the centering B, D, forwards. And note.-Respecting the slight
temporary centre C, before described, the same may be mounted, as before
mentioned, on pieces m, projecting out from the side walls, or else fixed fast on
the upper ends of slight upright props or legs set up close against each side
wall, and steadied at their upper ends by driving holdfasts into the walls, or
such legs may be set up with suitable struts on long horizontal feet, which
extend alongside of the side walls on the floor of the tunnel in the narrow
space between the side walls and the legs G, G, of the moving frame for the
centres, and after all the laggings have, one after another, been advanced
forwards from the temporary centre C, the same must then be advanced
forwards to the position shewn by the dotted linés P, Figure 3, in order to
place it under or within the hindmost ends of all the laggings L, L, in their
new or advanced position. That advance forwards may be easily performed by
lowering the slight centre C, by withdrawing wedges from under the lower ends
of its legs, and removing all it wedges p, p, so as to set the centre C quite
free, also removing the aforesaid holdfasts from the walls, and then moving the
long horizontal feet of the upright legs along the floor, much in the same
manner as the framing E, E, F, F, G, G, T, T, for the centres B and D); is
advanced; and those feet may have trucks, if requisite; and when the slight

page_text: centre C is thus advanced to its new position P, Figure 3, then its long feet
may be blocked and wedged up, so as to raise them off from bearing on such
trucks, and the upper ends of its legs are to be secured by holdfasts to the
said walls, and the centre Chaving been raised up so much by the said
wedging as to place it in contact with all the laggings, then the several
wedges p, p, are to be inserted, as before described, or otherwise; the slight
temporary centre C, whether it be set up on supports m, m, fixed into the side
walls, or supported on the tops of props set up against the side walls and
steadied by holdfasts, may be advanced forwards on a horizontal bearer fixed
temporarily under the vertex of the centre C, in a similar manner to that
already described for advancing the foremost centre A. The hindmost end of
the said horizontal bearer may be supported by a tall prop or ladder set up in
the middle of the tunnel, and its foremost end may be supported by the vertex
of the hindmost centre D when it is in its position, Figure 3, so that the said
bearer will become sufficiently fixed beneath the vertex of the centre C, to
sustain its weight, and it may be advanced along the bearer by pulling it
forwards with a rope. And note. In case the excavation in preparation for
receiving a further length of the tunnel is required to be begun and carried on
before the arching of the preceding length is constructed and keyed in, so as to
admit of lodging the hindmost ends of the supporting bars S, S, for the roof of
that new excavation on the foremost end of the arch, as is usually done (but
which foremost end is not yet built in the case now describing), then the said
bars
may be lodged on suitable blocks laid on the top of the foremost centre A,
with the hindmost ends of those bars S reaching backwards far enough beyond
the said blocks to become sustained by suitable blocking on the foremost end
of the arch as soon as the same is built, and after that is done, the blocks
before-mentioned being being removed from the top of the foremost centre will
leave the same at liberty when it requires to be advanced forwards. And
note.-Respecting the foremost part of the scaffolding V, V, Figure 1, whereon
the workmen are to stand, and which has been herein-before described as being
supported by the iron bearers W, W, and their suspending chains w, w, in
lieu of those bearers, the foremost portion of the said scaffold V, V, between
the centres A and B, may be united by hinges to the foremost horizontal cross
beam F, Figures 2 and 3, of the framing which supports the said centres B
and D, and the portion so hinged being suspended at its foremost end from
the foremost centre A by suspending chains w, w, then by letting loose those
chains, the said portion of the scaffold may be let to hang down vertically
across the tunnel beneath the cross beam F to which it is hinged, whereby it will
be sufficiently out of the way of the matter which is to be thrown down back-

page_text: wards from the face in excavating, and will also prevent fragments thereof falling
down so far backwards into the tunnel as some might otherwise do. But
when an explosion is about to be made with gunpowder, the said portion of
the scaffold which is so hanging vertically by its hinges may be hauled up so
much backwards from its vertical position beneath the cross beam F of the
hindmost centre D, as will take it sufficiently out of the way. And note.-In
closing up or keying in the crown of the arch after the two opposite sides
thereof have been built up by aid of the several laggings which have been
advanced forwards one after another, as above described, until only a narrow
space remains at the top between the two uppermost of the laggings so
brought forwards, then, in order to obtain access to the top for keying in the
crown of the arch, it is best to have no long- laggings at the very top of the
centerings, but to have a vacant space there that would otherwise require two
or three of the laggings to fill it up, also to form rebates at the upper and
inner edges of those two uppermost of the laggings which form the two sides
of that vacant space, and then short pieces of narrow board being lodged with
their two ends in those rebates will close the vacant space, so as to supply the
place of the two or three laggings which are omitted, and such boards may be
put in one after another, beginning with the bindmost, which will serve to
support the briks or key stones which are to join to the vertex or keying of
the toothing at the end of the preceding length of arch, and when thus much
of the keying of the arch and the filling up over it to the roof of the excavation
is well finished, then another narrow board is put up to sustain another short
portion of the keying and filling, which being performed, then another board is
put up, and so on until the whole length of the arch is completely keyed in,
and filled over at its crown. And note. Although I have devised only one
middlemost centre B, two or even more such may be used in cases when it is
desirable to give more support to the middle part of the laggings L, L, and to
have them of greater length than could be well supported by only one such
middlemost centre B; the mode of proceedure with two or more middle
centres, instead of the one marked B, will be the same as above described, and
in either case that middle centre or those middle centres may, if required, be
provided with a series of setting screws corresponding to those belonging to
*the hindermost centre D, for bearing up the mid-length of the several laggings
L, L, and also the said middlemost centres, if more than one, may, as before
mentioned respecting the one marked B, be made to take to pieces, and those
pieces may be laid down flat on the platform E, E, F, F, when the same is
advanced, so as by that means to enable the said centres to pass beneath the
cross braces or internal framing of the front centre A, if the same is so con-

page_text: structed; or without any taking to pieces, the said middlemost centres may, as
before mentioned respecting the one marked B, be turned down from their
proper vertical positions into horizontal positions, so as to lay flat on their plat-
form E, E, F, F, in order to enable the said centres to be advanced therewith
beneath cross braces of the front centre A, and the several feet whereby the
said middlemost centres stand upon the beams of their platform E, E, F, F,
may be united thereto with shackle or hinge joints, in order to facilitate the
said turning down and hoisting up without risk of any inconvenient displace-
ment of the said feet. And note. Also those said feet of the said middlemost
centres may have setting screws to raise them up or let them down, and others
to move them sideways across the arch, in order to bring each of the said
centres truly to their intended positions.
And my said improvements, as herein-before described, are applicable to the
construction of continuous arching, and other mining operations which require
such arching, besides those cases which are usually termed tunnels, viz., for
such as are called soughs, adits, underground drains or sewers; the arching
in such cases of underground work being of the same nature as in tunnels, the
mode of proceedure according to my improvements may be the same as herein-
before explained; and my said improvements are also applicable to the con-
struction of bridges and arches for railway, canal, or roadway passages, or for
warehouses or vaults, and for fire-proof buildings, as well as for underground
work, and will be advantageous in all such cases as require a greater .length
of continuous arching than can be conveniently constructed with one length of
centerings or supporters, and which therefore require the same to be removed
or advanced forwards; and my said improvements are also applicable to the
construction of arches by way of additional interior linings to tunnels which
have been finished but are defective, so that an interior portion of the original
thickness of the brickwork or masonry of the arching may require to be
removed in order to be replaced by a greater thickness of new arching. For
such cases the substance of my foremost centre A must be rather less in its
depth (measured in the direction of a radius to its curvature) than the intended
thickness of new work that is to be constructed together with the thickness of
the laggings which are to be used, and the mode of proceedure therewith will
be the same as before described, the new arching being built up within the
old, in the same manner as an original arching would be built up within the
excavated ground, and in cases where it may be necessary to construct such
additional work in a tunnel whilst the same continues in use for the passage
of barges or railway carriages and locomotive engines through the tunnel, the
same may be done by aid of my said improvements, without material difference

page_text: from what has been already described, except that: all the several centres B
and D, as well as A and C, must be made without any such cross ties or internal
framing as could interrupt the passing of barges or engines beneath the said
centres, wherefore the cross beams F, F, of the framing which is to support
the centres B and D must be omitted, and the longitudinal beams E, E, with
their legs G, G, and feet T, T, kept so close to the side walls as to be quite
out of the way of boats or engines passing through the tunnel; with that
condition the mode of proceedure may be much the same as herein-before
described, but as to the scaffolding on which the workmen are to stand, the
same must be fastened by hinges to each of the longitudinal beams E, E, and
held horizontally crossway of the tunnel, from each side thereof, by suspending
chains from the centres A, B, and D, so as to form shelves sufficiently wide
at each side for the workmen to stand upon, and whenever it is required to
make a clear passage for boats or engines to pass through the tunnel, then
the said scaffolding may be either let down by the said chains, in order to hang
down vertically on the said hinges so close to legs G, G, as to be out of the
way, or else may be hauled up by those chains on the said hinges into an
inclined position so close up against the centre A, B, and D as to be out of the
way, and when the workmen require the said scaffolding to be fixed higher up
in the arch as the building of it proceeds upwards, the said hinges are to be
removed from the beams E, E, and affixed to the centres A, B, D, at, such
heights therein as the work may require for the time. And whereas it may be
requisite in such cases of adding new lining to old work, to build the new with
some degree of conformity to the old, as to crookedness and slight deformity
of true curvature, the laggings may for that purpose be cut partly through
their thickness with a saw kerf. near to their mid-length, in order to render
them flexible just at the part which is to be supported by the middlemost
centre B, and that centre, as well as the hindmost centre B, being, as before
mentioned, provided with a series of setting screws f,f, the laggings may by
means thereof be set in or out of true curve and bended into such a degree of
conformity with the old work as may be desirable, and with the same, intent
small blockings of various thicknesses can be inserted between the foremost
ends of the several laggings and the prominent ledge e of the foremost centre A
by which those ends are supported; or each lagging may be made in two
lengths united by a link or simply hinge joint admitting of slight flexure,
care being in all cases taken that the said saw kerf or the said joint falls
just opposite the middlemost centre B, B. And note.-Instead of the
series of setting screws f,f, with which the hindmost centre D is provided, and
with which the middlemost centre or centres B may also be provided, as

page_text: herein-before described; wedges may be inserted between the external cir-
cumference of the centre and each of the several laggings, the lengthway of
those wedges being horizontal and in the direction of the laggings, with one
such wedge to each lagging, wherefore, by driving in or withdrawing those
wedges, the same effects of supporting all the several laggings may be produced
as by the setting screws f,f, herein-before described.
Having now described my said improvements, I, the said Joseph Fraser, do
hereby declare that the new Invention whereof the exclusive use is granted
to me by the aforesaid Letters Patent consists in the new arrangement and
combination of the apparatus or machinery herein-before described, to be
employed as centerings or supporters in the construction of bridges and arches
and in tunnels and other mining operations; the characteristic of that new
combination and arrangement whereby it is distinguished from the centerings or
supporters heretofore used being, first, that the foremost or most advanced of the
centres or supporters which is to bear the foremost ends of the laggings whereon
the bridge, arch, or tunnel is to be constructed or built is not as heretofore an
interior centering to the intended arch, but the said foremost or most advanced
centre or support stands at the end of the arch that is to be constructed or
built, the chief part of its substance being in the space which will be afterwards
occupied by the brickwork or masonory of a future length of the arch, and
standing opposite to the place of the toothing which is to be left at the end of
the arch for joining with that future length; the said foremost or most advanced
centre or support sustaining the foremost ends of the laggings by a suitable
connexion of these ends with its interior or concave edge, and the two ends or
feet of the said foremost centre or support standing with suitable sole plates,
blocks, and means of adjustment, upon advanced portions of the two side walls
from which the arch is to spring, and the hindmost vertical face of the said
foremost or most advanced centre or support having a suitable pattern for the
intended courses of brickwork or masonry formed in relief upon it, or marked
upon it, to serve as guides for the laying of such courses, all which has been
herein-before fully explained.
Secondly, the addition of a slight temporary centre to sustain the hindmost
ends of the laggings quite independently of the main centres, for the support
of the laggings whilst the arch is building, and before it is closed or keyed in
at the top or crown, and which slight temporary centre is set up with its two
feet or ends standing (with suitable means of adjustment) upon supports fixed
into the side walls, and projecting out therefrom, or on the ends of props reared
up against those side walls.
Thirdly, that the other centres or supporters, which are to bear the hindmost

page_text: ends and the mid-length of the laggings whilst the arch is building on them, are.
erected and supported on a moveable frame or platform which is let down to rest
on trucks or wheels (after the arch is closed or keyed in and the said centres are
lowered so much by such letting down as to quit contact with the laggings (leaving
the same undisturbed and supported by the foremost or most advanced centre,
and by the slight temporary centre), whilst the said frame or platform, with the
hindmost and middle centres, is moved or advanced forwards on its trucks or
wheels, in order to carry the middlemost centre or centres beneath the fore-
most or most advanced centre. And note. If the latter is made with cross
bars or internal framing, either those bars or framing must be removed in
manner herein-before described, or the said middlemost centre or centres must
be taken to pieces or laid down flatways on the said moveable frame or plat-
form, in manner herein-before described, in order that it or they may be so
carried beneath the said foremost centre as aforesaid; and the said moving or
advancing forwards of the frame or platform being continued until it has
carried the hindmost centre close up to the front or most advanced centre, then-
the frame or platform is raised up so much as to take it off its trucks or
wheels, and as to carry up the hindmost centre in contact with the foremost
ends of the laggings, and that contact is made complete, with all the several
laggings, by aid of the series of setting screws or of wedges, with which the
hindmost centre is provided, as herein-before described; and after that contact
has been made complete, the front or most advanced centre may be moved or
advanced forwards, leaving the laggings undisturbed and resting on the slight
temporary centre and the hindmost centre, in order to support the arching.
Fourthly, that the several centerings or supporters to be used in the con-
struction of arching within underground tunnels are made with metal
extending all the way around the curve; and if made in pieces of metal, the
same are strongly united by revitting or screwing metal to metal, so as to
preserve a continuity of metal throughout the curve, and each centre consisting
of one such continuous curve of metal, or of two or more such curves com-
bined together, and which may have wood interposed between them or other-
wise combined with them, in order by such application of continuous metal
curves to give sufficient strength to the curved portion of the centre to enable
it to be formed like a simple bow or arch, as herein-before explained, having all
the matter which is to give it strength disposed in its curve without requiring
internal framing (or at most only a cross tye or string to bow), whereby the
space within such centre is left clear for the operations of the workmen to be
carried on without the embarrassment and crouding that is caused by the
cumbrous internal framing of wood usually employed in centrings. But note.-