IMPROVEMENTS IN OBTAINING AND APPLYING MOTIVE POWER, WHICH IM- PROVEMENTS OR PARTS THEREOF ARE APPLICABLE FOR RAISING, FORCING, AND MEASURING FLUIDS
Year: 1863

page_text: LETTERS PATENT to Robert William Thomson, of Edinburgh, in the
County of Mid Lothian, North Britain, Civil Engineer, for the Invention
of "IMPROVEMENTS IN OBTAINING AND APPLYING MOTIVE POWER, WHICH IM-
PROVEMENTS OR PARTS THEREOF ARE APPLICABLE FOR RAISING, FORCING, AND
MEASURING FLUIDS."
Sealed the 12th May 1868, and dated the 24th February 1863.
PROVISIONAL SPECIFICATION left by the said Robert William Thomson
at the Office of the Commissioners of Patents, with his Petition, on the
24th February 1863.
I, ROBERT WILLIAM THOMSON, of Edinburgh, in the County of Mid Lothian,
North Britain, Civil Engineer, do hereby declare the nature of the said
Invention of "IMPROVEMENTS IN OBTAINING AND APPLYING MOTIVE POWER, WHICH
IMPROVEMENTS OR PARTS THEREOF ARE APPLICABLE FOR RAISING, FORCING, AND
MEASURING FLUIDS," to be as follows, that is to say:-
This Invention relates in the main to the arrangement and construction of
an improved rotatory steam engine, which consists of a cylinder or steam
chamber with a horizontal axis containing within it two diaphragms or pistons.
One of these pistons or diaphragms is keyed upon a solid shaft passing through
the axial line of the cylinder, whilst the other is similarly keyed upon or attached
to a tubular or hollow shaft through which the solid shaft is passed. The hollow
or tubular shaft passes out of one end of the steam cylinder by a stuffing box
in the ordinary manner, and the solid shaft passes through it.
keyed upon it a working crank, and these two cranks have
Each shaft has
connecting rods,

page_text: the opposite ends of which are jointed to the rim of a fly-wheel disposed eccen-
trically as regards the steam cylinder by means of suitable joint studs. The
positions of the pistons accord with those of the external cranks, and the
actuating steam is admitted to one side of the pistons or diaphragms, and
discharged on the other by valves of any suitable form. At the "dead point"
of the engine, the two pistons or diaphragms themselves close the steam
cylinder ports. If now the fly-wheel moves round, one piston will pass the
induction port, and the other will pass the eduction port, both moving in
the same direction; but when steam enters by the induction port it tends to
cause the two pistons to move in opposite directions. But as the two pistons
are set to revolve upon one main centre, and are connected by the cranks and
connecting rods with the fly wheel as herein-before referred to, working upon
a separate and independent centre, it follows that the front or first piston will
increase in volocity, whilst the opposite or second piston decreases in speed;
the steam being introduced between the two. The result is that during a
complete revolution of the fly wheel each of the pistons will traverse three-
quarters of a revolution with the actuating steam pressure, and one quarter of
a revolution against it, giving together a working traverse equal to one-and-
a-half revolutions. During this amount of traverse each of the pistons is
working through a quarter of a revolution against the pressure of the steam,
and this being deducted from the amount of forward motion leaves a com-
plete revolution of the pistons corresponding to that of the fly wheel, with
the pressure of the steam available as power. This rotatory engine may be
so arranged as to dispense with slide valves, the pistons being made available
to open and shut the steam ports at the proper intervals.
In another arrangement of the engine the crank pins before referred to
instead of being connected to the fly wheel by rods, are made to enter slides
which traverse to and fro in a slot formed in a bar extending across the face
of the fly wheel. In lieu of this arrangement the differential movement may
be obtained by means of a system of eccentric elliptical wheels gearing
together. On the axle of the fly wheel are keyed two of these wheels, one of
which gears with a corresponding wheel on the hollow shaft on which one of
the diaphragms or pistons is keyed, whilst the other wheel gears in a similar
manner with a corresponding wheel on the shaft of the other diaphragm or
piston. Owing to the eccentricity of these wheels, one piston is caused to
travel with greater velocity than the other, thus causing the peculiar kind of
differential movement before referred to. One of the diaphragms will thus
travel through three-fourths of a revolution with the full pressure of steam,
whilst the other traverses a fourth of a revolution against that pressure..

page_text: This principle of construction is also applicable to the raising and forcing
of fluids, which is effected by simply applying power to the main shaft for the
purpose of producing rotatory motion, and connecting the suction pipe to the
induction port. The apparatus is also with trifling modifications rendered
particularly applicable for measuring fluids, and indicating the quantity passed
through the machine. The fluid is admitted at the induction port, its pres-
sure serving to drive the diaphragms or pistons in place of the pressure of
steam as before described. The cylinder of the meter is made of a suitable
capacity to contain a given quantity of fluid, and the number of revolutions
of the diaphragms or pistons are shown on dial plates by means of a train of
wheels in connection with the diaphragms or pistons, and driven therefrom.
In this way the quantity of a fluid passing through a pipe or pipes may be
accurately measured and registered with great facility.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Robert William Thomson in the Great Seal Patent Office on
the 24th August 1863.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ROBERT
WILLIAM THOMSON, of Edinburgh, in the County of Mid Lothian, North
Britain, Civil Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-fourth day of February, in the year of
our Lord One thousand eight hundred and sixty-three, in the twenty-sixth
year of Her reign, did, for Herself, Her heirs and successors, give and
grant unto me, the said Robert William Thomson, Her special license that
I, the said Robert William Thomson, my executors, administrators, and
assigns, or such others as I, the said Robert William Thomson, my executors,
administrators, or 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 OBTAINING AND APPLYING
MOTIVE POWER, WHICH IMPROVEMENTS OR PARTS THEREOF ARE APPLICABLE FOR
RAISING, FORCING, AND MEASURING FLUIDS," upon the condition (amongst others)
that I, the said Robert William Thomson, my executors or administrators, by
an instrument in writing under my hand and seal, or under the hand and seal
of one of them, should particularly describe and ascertain the nature of the

page_text: 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 Robert William Thomson, do hereby
declare the nature of my said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by the
following statement, reference being had to the accompanying Drawings, and
to the letters and figures marked thereon, that is to say :-
My said Invention relates, in the main, to the arrangement and con-
struction of an improved rotatory steam engine, which consists of a cylinder or
steam chamber with a horizontal axis, containing within it two diaphragms
or pistons. One of these pistons or diaphragms is keyed upon a solid shaft
passing through the axial line of the cylinder, whilst the other is similarly
keyed upon or attached to a tubular or hollow shaft, through which the solid
shaft is passed. The hollow or tubular shaft passes out of one end of the
steam cylinder by a stuffing box in the ordinary manner, and the solid shaft
passes through it. Each shaft has keyed upon it a working crank, and these
two cranks have connecting rods, the opposite ends of which are jointed to
the rim of a fly wheel disposed eccentrically as regards the steam cylinder by
means of suitable joint studs. The positions of the pistons accord with those
of the external cranks, and the actuating steam is admitted to one side of the
pistons or diaphragms, and discharged on the other by valves of any suitable
form. At the "dead point" of the engine the two pistons or diaphragms
themselves close the steam cylinder ports. If now the fly wheel moves round,
one piston will pass the induction port and the other will pass the eduction
port, both moving in the same direction; but when steam enters by the
induction port it tends to cause the two pistons to move in opposite directions;
but as the two pistons are set to revolve upon one main centre, and are con-
nected by the cranks and connecting rods with the fly wheel, as herein-before
referred to, working upon a separate and independent centre, it follows that
the front or first piston will increase in velocity, whilst the opposite or second
piston decreases in speed, the steam being introduced between the two. The
result is, that during a complete revolution of the fly wheel each of the pistons
will traverse three-quarters of a revolution with the actuating steam pressure,
and one quarter of a revolution against it, giving together a working traverse
equal to one-and-a-half revolutions. During this amount of traverse each
of the pistons is working through a quarter of a revolution against the pressure
of the steam, and this being deducted from the amount of forward motion,
leaves a complete revolution of the pistons corresponding to that of the fly

page_text: wheel with the pressure of the steam available as power. This rotatory engine
may be so arranged as to dispense with slide valves, the pistons being made
available to open and shut the steam ports at the proper intervals. In another
arrangement of the engine the crank pins, before referred to, instead of being
connected to the fly wheel by rods, are made to enter slides which traverse
to and fro in a slot formed in a bar extending across the face of the fly wheel.
In lieu of this arrangement, the differential movement may be obtained by
means of a system of eccentric elliptical wheels gearing together. On the
axle of the fly wheel are keyed two of these wheels, one of which gears with
a corresponding wheel on the hollow shaft, on which one of the diaphragms or
pistons is keyed, whilst the other wheel gears in a similar manner with a
corresponding wheel on the shaft of the other diaphragm or piston. Owing to
the eccentricity of these wheels one piston is caused to travel with greater
velocity than the other, thus causing the peculiar kind of differential move-
ment before referred to. One of the diaphragms will thus travel through
three-fourths of a revolution with the full pressure of steam, whilst the other
traverses a fourth of a revolution against that pressure. This principle of
construction is also applicable to the raising and forcing of fluids, which is
effected by simply applying power to the main shaft for the purpose of pro-
ducing rotatory motion, and connecting the suction pipe to the induction port.
The apparatus is also, with trifling modifications, rendered particularly appli-
cable for measuring fluids and indicating the quantity passed through the
machine. The fluid is admitted at the induction port, its pressure serving to
drive the diaphragms or pistons in place of the pressure of steam, as before
described. The cylinder of the meter is made of a suitable capacity to contain
a given quantity of fluid, and the number of revolutions of the diaphragms or
pistons are shown on dial plates by means of a train of wheels in connection
with the diaphragms or pistons, and driven therefrom. In this way the
quantity of a fluid passing through a pipe or pipes may be accurately measured
and registered with great facility.
And in order that my said Invention of "Improvements in Obtaining and
Applying Motive Power, which Improvements or Parts thereof are applicable
for Raising, Forcing, and Measuring Fluids" may be properly understood, I'
shall new proceed to describe the several Figures on the explanatory Sheets
of Drawings, which I have hereunto appended for the purpose of showing
certain modifications under which my Invention may be judiciously carried out
in practice, that is to say:-
Figure 1 on Sheet 1 of the accompanying Drawings is an elevation,
partially in section, of one arrangement of a rotatory engine constructed

page_text: according to my improvements, and Figure 2 is a plan of the same; Figure 3
is an elevation, partially in section, of the second modification of the rotatory
engine; Figure 4 is a partly sectional elevation of an engine arranged with
elliptical gearing in lieu of the details shown in Figures 1, 2, and 3; and
Figure 5 is a plan corresponding to Figure 4.
Referring to the modification delineated in Figures 1 and 2, the foundation
or substructure A supports the framing B, which consists of an open rectangular
frame of cast iron, which is bolted down to the beams of timber beneath. The
open frame is constructed with two longitudinal beams, on which as well as on
the frame itself are arranged the principal bearings of the engine. The steam
chamber or cylinder C of the engine is of a cylindrical figure in the end view,
or when viewed as shown in Figure 1, that is to say, it is a cylindrical chamber
internally with vertical ends, which are bolted up to the central part. On the
upper part of this steam chamber or cylinder is arranged the valve chest D,
into which the steam pipe E leading from the neighbouring boiler opens. In
the valve chest D is fitted the slide valve F, which moves to and fro by the
action of the eccentric over one of the ports of the two-way valve G, by means
of which the action of the engine is reversed, when required, by means of the
hand lever G. The spindle H of the valve F extends out through a stuffing
box in the end of the valve chest E, and has fitted on it the hand wheel I, and
at this part it is connected by the links J to the lever arm K on the rocking
shaft L, the connection of which with the eccentric on the main shaft of the
engine will be presently referred to. The bearings of the rocking shaft L are
carried in the standards M, which are bolted down to the framing of the
engine. The steam after it passes through the valves F and G enters the
cylinder C by one of the ports N or N', and as the valve G is delineated in
the Drawing, it is in the position to admit the steam by the right-hand port N.
The steam passes into the cylinder C, and here it acts on two pistons,
which form a species of diaphragm occupying nearly one half of the interior of
the cylinder. These piston are fitted in the following manner :-A short hori-
zontal shaft O extends across the centre of the cylinder and out through the
end covers. Upon this solid shaft O is fitted a secondary tubular shaft P,
which extends out through one of the stuffing boxes in the end covers of the
cylinder. This tubular shaft P extends from the inner stuffing box of the
cylinder halfway along the shaft O, so as to admit of one portion of the duplex
piston being fitted to the uncovered part of the shaft O and the other portion
to the shaft P. The two parts of the piston are of a sectorial figure when seen
in end view or as shown in vertical section in Figure 1; the left-hand part Q
is keyed to the solid shaft O, and the other part R is keyed to the tubular

page_text: shaft P.
These pistons nt loosely in the cylinder C, so that the steam nas
access between the periphery of each part, and the inner surface of the cylinder
excepting at the part where the metallic stuffing S is fitted in a groove which
extends across each piston. The inner end of the shaft O which extends out
beyond the hollow shaft P terminates in a crank T, and the pin of this crank
is connected by the rod T¹ to a stud in the rim of the fly wheel U. In like
manner the hollow shaft P has keyed to it the crank V, which is connected by
the rod V to the fly wheel U. This fly wheel is keyed on the main shaft W
of the engine, which shaft is carried in pedestal bearings bolted down to the
rectangular frame B, the axial line of the shaft being eccentric to the centres
of the shafts O and P. On the shaft W is fitted the eccentric X, which is con-
nected by the rod Y to a lever arm on the rocking shaft L, and so gives
motion to the slide valve F. Let it be supposed that the engine is to bo
moved in the direction of the arrows shown in Figure 1, when the flywheel is
moved round a little by hand so as to open the port N, the steam flows in and
moves round the piston R. The steam acting on the surface of the piston R
tends to force it round in the direction of the arrow, at the same time, however,
the steam acts on the piston Q and tends to force it in the opposite direction to
that of the piston R; but since the piston R will move through three-quarters
of a revolution, whilst the piston Q moves only through a fourth of a revo-
lution, this differential movement is made available as motive power. Thus,
if the fly wheel U starts when the other moving parts are in the position shown
in Figure 1, when it has made one-fourth of a revolution the piston R will
have made about three-eighths of a revolution, whilst the piston Q will have
travelled through only about one-eighth of a revolution; and when the fly
wheel has made one-half of a revolution, the piston R will have travelled round
to the position in which the piston Q is shown. Thus for each half revolution
of the fly wheel U, the pistons Q and R make alternately three-fourths of a
revolution and alternately one-fourth of a revolution. In this way during each
complete revolution of the fly wheel U, each of the pistons will traverse
through three-fourths of a revolution, making together a traverse of one-and-
a-half revolutions of forward movement; against this is to be placed one-half
of a revolution, in which the pistons have to be dragged against the pressure
of the steam, and this being deducted from the amount of forward movement
just referred to, leaves for each revolution of the fly wheel one complete revo-
lution of the pistons available for power. The movement of the piston opens
the eduction port N', and the steam, after doing its work, passes through the
eduction, and away by the exhaust Z. The valve G has its spindle connected
to the hand lever G¹, by means of which the valve may be readily shifted, so

page_text: as to cause the port N¹ to be the induction port, and thus reverse the motion
of the engine. The spindle H of the valve I has a right and left-handed
screw formed on its extremity, and by means of the hand wheel I, the position
of the slide valve F may be adjusted as as regards the ports in the valve G,
and the amount of the "lap" be regulated as required. In the modifi-
cation delineated in Figure 3 on Sheet 1 of the accompanying Drawings, the
system of connecting the cranks by means of rods is dispensed with, and in
lieu thereof the crank pins enter into slides, which traverse in a slot formed
on the face of the fly wheel. The parts of this engine which correspond to
those shown in Figure 1, are marked with corresponding letters of reference.
The pins of the cranks T and V on the shafts O and P enter the slides T' and
V₁, which traverse to and fro in a slot which is formed in the rectangular
frame a. This frame is bolted up to or is cast on to the face of the fly
wheel U, it is delineated in the horizontal and vertical directions showing the
two positions of the cranks when the fly wheel has made one-fourth of a revo-
lution. With the exception of this portion of the details, the other parts of
the engine correspond in construction and mode of operation with the modifi-
cation shown in Figure 1, and therefore need not be repeated.
:
Figure 4 is an elevation, partially in section, of another modification of the
engine, arranged with elliptical eccentric wheels in lieu of the cranks, and
Figure 5 is a plan of the same. This engine is arranged on an open rec-
tangular framing B, varying but little from that shown in Figures 1 and 2;
within the central open part of this framing is arranged the cylinder C, which
is similar to that herein-before described. Steam is admitted to the cylinder
by the inlet pipe E, the quantity being regulated by the valve in the valve
box F. The shafts O and P, to which the parts Q and R of the piston are
keyed, are arranged with the inner ends abutting, as shown in the sectional
view Figure 1 on Sheet 2 of the accompanying Drawings. The ends of the
shafts project out beyond the cylinder C, and are carried in pedestal bearings
arranged on the transverse beams of the framing B. The inner ends of the
shafts O and P have keyed to them the pistons Q and R, one to each shaft.
The mechanical details of this part of the engine will be more particularly
referred to in describing the Figures on Sheet 2 of the accompanying
Drawings. To the outer part of each of the shafts O is keyed an elliptical
eccentric wheel; these wheels T and V gear with the corresponding wheels
T' and V', which are keyed on the main shaft W carrying the fly wheel U.
When the induction port N is opened the steam passes in between the two
pistons Q and R, and owing to the peculiar arrangement of the eccentric
wheels the piston Q is driven round at a higher velocity than the other

page_text: piston R, and the same kind of differential movement is brought about as in
the modification shown in Figures 1, 2, and 3, and herein-before described.
The used steam after completing its work in actuating the piston passes away
by the outlet pipe Z, as indicated by the arrow in Figure 4.
Another modification of this arrangement of rotatory engine is delineated in
Sheet 2 of the accompanying Drawings. Figure 1 is a front elevation of the
engine partly in section; Figure 2 is an end view of the same, with the cylinder
cover removed, and showing one of the pistons in section; and Figure 3 is a
plan corresponding to Figures 1 and 2. A heavy cast-iron frame B is bolted
down to the foundation, and to this framing is bolted the cylinder or steam
chamber C. The steam passes into this chamber by the inlet pipe E, and acts
on the pistons Q and R, in the manner herein-before described. The manner
in which the pistons are arranged on the shafts O and P, as well as the con-
struction of the same, is shown in Figure 1. The cylinder C is formed with
a tubular bush 6 at the central part, which is divided at the middle to allow
of the connection of the pistons with the shafts O and P. These shafts have
their ends abutting, as shown in the Drawing, and on these extremities are
fitted the two pistons Q and R. The shafts O and P revolve in the tubular
bearings c, and the whole is kept steam-tight by the elastic stuffing d, outside
of which is placed a metal disc e, and this is pressed up to any required extent
by means of the outer disc f, the pressure of which is adjusted by the screws g
pass through the boss of the contiguous wheel V; the opposite end of the
shaft next the wheel T being fitted in like manner. The sectional pistons
Q and R are bolted to the laterally projecting arms h, apertures being formed
in the ends of the pistons to admit of access to the interior; these apertures
are then closed by the screw plugs i. The arrangement of the metallic
packing to prevent the passage of the steam past each sector of the piston is
shown in the lower part of Figure 1 on Sheet 2. A groove is formed in each
face of the sector, and in this recess are fitted the blade springs j, which press
the steel bars k outwards, and in steam-tight contact with the contiguous
surfaces of the cylinder C.
that
These details of arrangement may, however, be modified in various ways.
On the shafts O and P are keyed the elliptical eccentric wheels T and V,
which gear with the corresponding wheels T and V', carried on the overhead
shaft W. This shaft is carried in pedestal bearings formed on the upper part
of the cylinder C, and on the outer extremity of which is keyed the fly
wheel U. The used steam after operating in the manner herein-before
described passes off by the exhaust Z.

page_text: These engines may also be advantageously employed for raising water or for
propelling it in any desired direction... For this purpose the suction pipe is
connected to the inlet pipe E, and power is applied to drive the shaft W, and
the water flows off by the pipe Z.
The modification delineated in Figure 4 on Sheet 2 of the accompanying
Drawings shows the arrangement of a pair of compound engines as applied to
actuate tho shaft of a screw propeller, or for other generally similar purposes.
These engines are of the double-cylinder class, the two cylinders of each
engine being arranged one above the other, as shown, the high-pressure steam
is admitted first into the cylinders C of the smaller engines, and then into the
larger cylinders C¹ beneath. The steam flows in by the inlet pipe E into the
valve chest D, in which is fitted the double valve F that controls the passage
of the steam to the two high-pressure cylinders C, and after acting on the
pistons Qand R in each cylinder, it passes off by the exhaust Z into the steam
passages and, and into the valve chest G, which is divided by a partition m
in the centre, through which the spindle H. of the valves H
passes. From
the upper cylinders C the steam is conveyed into the diagonally opposite
cylinders C, so that one pair of the cylinders C and C¹, namely, the right-
hand upper cylinder, and the left-hand lower one, are working at the most
effective portion of their stroke, whilst the other two are at their dead points.
The shafts O and P, and the sectorial pistons Q and R, are arranged in the
same manner as those herein-before described, and on the outer extremities of
the shafts are keyed the elliptical eccentric gearing, which is indicated by the
ovals T and T', drawn in red lines, and by those drawn in black V and V¹, the
former being those supposed to be in front of the engine,' and 'the latter those
on the further side. Each pair of these elliptical wheels is in gear with the
wheels T and V' on the propeller shaft W. The two-valve spindles F and H,
which project out through stuffing-boxes in, the ends of the valve chests, are
coupled by means of a cross head not shown in the Drawing, this cross head is
connected to a hand lever, by moving which the action of the engines may be
simultaneously reversed. The used steam, after working the pistons of the
cylinders C, passes off by the exhausts to the condenser. To avoid any
irregularity or "back lash" in the eccentric gearing, each wheel on one side
of the engine is connected by a rod p to a pin n projecting out from the face
of the wheel T' and V' on the propeller shaft W. In arranging these con-
necting rods, the studs must be fitted in the foci of the excentric wheels, as
shown in the Figure.. This arrangement keeps the gearing quite steady in its
traverso as the pistons pass the dead points.

page_text: .
In Figures 5 and 6, on Sheet 2, is shown another mode of coupling a pair
of rotatory engines with a propeller or other shaft. The shafts O and P are
arranged in the same manner as shown in Figure 1 on the same Sheet, and
the cranks T and V are connected by the links T' and V with the long
cranks U, which are the equivalent of the fly wheel U, shown in Figures 1
and 2 on Sheet 1. These cranks are keyed to the intermediate shafts W,
which are cranked and are connected by the triangular system of rods q with
the main shaft o. The cranks on the near or front side of the engine in
Figure 5 are shown in full lines, and those on the further side are indicated
by the red lines r, these cranks q¹ being set so that there is a quarter of a
revolution of difference between them and those on the opposite side of the
engine. The paths of the several cranks are indicated by the blue lines s.
With trifling modifications this system of coupling may be applied to the
compound engine shown in Figure 4 on the same Sheet..
Figures 7 and 8 show another modification of the rotatory engine; Figure 7
is an elevation of the engine, and Figure 8 a transverse sectional plan of the
same. The cylinder C is made with a cover C, which is arranged so that it
rotates with one of the pistons. This end cover is made with a deep central
bush, in which is fitted the conical brass bush c', and the stuffing d. The
opposite end cover C¹ is also arranged with a laterally projecting bush, in
which is arranged the conical bush c. The shaft O is formed in one piece,
and the conical parts of it work in the bushes c and c', as shown in Figure 8..
The two pistons Q and R are the same in construction as before described.
The piston R is connected to the cylinder cover C, whilst the piston Qis
keyed to the shaft O. Projecting out from the face of the cover C is a pin T,
which is connected by the rod T to a pin in the rim of the fly wheel U, the
axle W of which is eccentric to the axis of the cylinder C. The shaft O has
keyed to its outer extremity the crank V, which is connected by the rod V₁ to
the rim of the fly wheel U. The working of this engine is the same as those
before described, but its arrangement obviates the use of the shaft P shown
in the other Figures on the same Sheet: The diagram shown in Figure 9 is
a transverse vertical section taken through the cylinder of a. double-acting
engine, or one arranged with four steam ports and two double pistons. The
steam ports are arranged in this instance at a distance of 45 degrees between,
each pair of ports, but the distance between them may be varied, as required.
The ports N, which are diametrically opposite, are the induction ports, and
the ports N¹ are the eduction ports, but both of these can be altered by
reversing the positions of the valves as before described, the two shafts O and P
are arranged as shown in Figure 1 on the same Sheet, and on one shaft is.

page_text: keyed the piston Q, and on the other the piston R, so that both act in unison.
Each of these pistons is made with two sectors, and as the steam enters the
induction ports both pistons are acted on simultaneously. Thus as the steam
enters by the induction ports N, the piston Q traverses through three-eighths
of a revolution, and takes the position in which the piston R is shown in the
Figure. Meanwhile the piston R has traversed through only one-eighth of a
revolution, and then occupies the position in which the piston Q is shown.
The piston R now becomes the driving piston of the engine, and when this
piston has traversed through three-eighths of a revolution, the piston Q has
traversed one-eighth, each pistón having then completed a half revolution, and
driven the main shaft W through a corresponding space. This arrangement
of the engine involves the necessity of using double-lobed wheels T and V on
the shafts O and P, and the corresponding wheels T¹ and V on the main shaft W,
the pitch lines of these wheels being merely shown in the Figure. As the cur-
vature of the pitch lines of these wheels varies in proportion to the angular
distance between the ports, I will now give proper rules for obtaining the pitch
lines of wheels suitable for any given angular distance between the ports.
Thus, to obtain the pitch lines of the wheels suitable for working with a single-
acting engine, similar to that shown in Figure 4, in Sheet 1, having its ports
90 degrees apart, as shown by the dotted lines at a, P, b, in Figure 9, Sheet 2,
the following is the rule:-When the following data are given, the angle of
the sector-shaped pistons Q and R, (which is also very nearly the angular
distance between the ports,) and the line of centres or distance between the
centres of the two shafts P and W; (which is also the greater axis of the pitch
line of each of the elliptic wheels,) the following is the construction for finding
the proper eccentricity of each of those pitch lines. Draw A, B, Figure 10,
to represent the said line of centres or greater axis; draw B, C, perpendicular
to A, B, and A, C, making the angle B, A, C, equal to one-half of the given
angle between the ports, or 45 degrees, so as to form a right-angled triangle
A, B, C; from C, A, cut off C, E, equal to C, B, then A, E, will be the double
of the eccentricity; in other words, A, E, will be the distance between the
foci of each of the elliptic pitch lines. Figure 11 shows the pitch line of a
wheel constructed according to this rule and suitable for the angular distance
a, b, Figure 13, or 90 degrees.
Second, when the following data are given the angle of the sector-shaped
pistons, (which is also very nearly the angular distance between the ports,) and
the line of centres or distance between the centres of the two shafts, the
following is the rule for constructing the pitch line of each of the wheels suited to
make the pistons approach and recede from each other twice in each revolution,

page_text: (which may be called two-lobed wheels.) With the aid of the first rule, as
illustrated by Figure 10, draw one-half of the elliptic pitch line suitable for a
sector-shaped piston of double the given angle. Let C, 1, 2, 3, 4, 5, 6, 7, B,
in Figure 11, represent the half ellipse so drawn, C, B, its greater axis (being
equal to the distance' between the centres), P, W, and A, one of its foci.
From that focus draw any convenient number of radii, such as A, A, A³, &c,,
making equal angles with each other; then take a point D, Figure 12, to
represent the centre of the required pitch line, from which draw at right angles
to each other D, E, equal to A, B, and D, F, equal to A, C, and from D,
draw a set of radii D¹, D, D³, &c., equal in number to the radii drawn from A,
and making with each other angles each of which is equal to one-half of the
corresponding angle at A, Figure 11; then make each of those radii drawn
from D, equal to the corresponding radii drawn from A, that is to say D¹,
equal to A'; D, equal to A³, &c., and through the ends of those radii draw a
curve E, F, this will give one quadrant of the required pitch line, which will
consist of four similar quadrants. This process may be illustrated by con-
ceiving the radii of the original semi-ellipse A, C, A', A2, &c., to be the sticks
of a fan, which are at first spread out over an angular space of 180°, but in
the new Figure are closed together into the angular. space of 90° between
D, E, and E, F, each angle in the new Figure being exactly one half of the
corresponding angle in the original Figure. By diminishing each angle to
one-third, one-fourth, or any other aliquot part of the corresponding original
angle, a pitch line may be obtained for three-lobed, four-lobed, or other many
lobed wheels, suitable for producing the required approach and recession of
the pistons three times, four times, or any other number of times in one
revolution; the number of ports and pistons must be in proportion to the
number of lobes on the wheels, and in this way the pitch lines of double-lobed
wheels suitable for double-acting engines, as shown in Figure 9, are obtained.
Third, when it is desired that the fly shaft should make one revolution for,
two or more revolutions of the pistons, or two or more revolutions for one
revolution of the pistons, or generally, that the pistons and the fly shaft should
make different numbers of revolutions in the same time, the wheels with
which they are respectively connected must have different numbers of lobes,
those numbers of lobes being inversely as their speeds; and an elliptic wheel.
being considered as a one-lobed wheel. It then becomes necessary to con-
struct wheels of different numbers of lobes which shall work correctly together
as follows:-Design the wheel connected with a piston according to rules 1
and 2. Then, in Figure 13, describe about the point A, a circle of a radius
A, C, equal to the eccentricity of the said wheel if it is an ellipse, or equal to

page_text: half the difference of its greatest and least radii if it has two or more lobes.
Draw a diameter D, A, C, and produce it to B, making A, B, equal to the
mean radius of the wheel, (or in an ellipse half the greater axis,) so that B, C,
will be the least, and B, D, the greatest radius. From B, draw B, E, touching
the circle at the point E; then in that tangent, (produced if necessary,) take
E, F, according to the following proportion:-As the number of lobes in the
wheel connected with the piston: is to the number of lobes in the wheel on
the fly shaft so is E, B, to E, F. From F, draw the line F, A, through the
centre of the circle, cutting it in G and H; then F, G, will be the least, and
FH, the greatest radius of the wheel required, which can then be constructed
according to rules 1 and 2. Thus the curved line c, d, shows a quadrant of a
wheel suitable for a single-acting engine in which the fly wheel is required to
make one revolution to two of the engine; and Figure 11 shows the pitch line
of the pinion to work with this wheel. In applying this rule the length of the
line of centres P, W, are not fixed until the dimensions of the pitch lines of the
wheels have been determined, when it will be equal to the greatest radius A, e,
Figure 13, of one pitch line, added to the least radius A, C, of the pinion,
Figure 11, and A, I, is equal in this case to the line of centres P, W, Figure 9.
The several modifications of engines herein-before described and shown in
the accompanying Drawings may be advantageously arranged for and applied
as blowing engines, pumps for condensing engines, and for fire engines, for
exhausting gas from retorts and forcing it into gasometers, and other generally
similar purposes. Machines constructed on this principle and of a suitable
In this case the
size may
y also be conveniently used for measuring fluids.
fluid to be measured passes into the machine where its pressure serves to drive
the pistons, the number of revolutions of which is indicated by a train of
wheels similar to the indicating arrangement of an ordinary gas meter. The
internal space in the cylinder to which the fluid is admitted being of a given
capacity, it follows that the quantity passed through the machine will be
registered accurately.
Having now described and particularly ascertained the nature of my said
Invention, and the manner in which the same is or may be used or carried
into effect, I would observe in conclusion, that what I consider novel and
original, and therefore claim as the Invention secured to me by the herein-
before in part recited Letters Patent is,-
First, the system or mode of arranging and constructing rotatory engines or
machines on the principles herein-before referred to, namely, the obtaining of a
differential movement of two or more pistons, the difference of traverse of the
pistons being available as power, this difference being obtained by the peculiar

page_text: arrangement and combination of the several parts, as herein-before described
and shown in the accompanying Drawings.
Second, the arrangement of the main or driven shaft in relation to the axis
of the cylinder or steam chamber, together with the arrangement and com-
bination of the parts by means of which the differential motion of the pistons
is caused, as herein-before described and shown in the accompanying
Drawings.
Third, the application to and use of the differential movement of two or
more pistons working within a suitable chamber or vessel as a motive power,
and for raising, forcing, measuring, and exhausting fluids.
In witness whereof, I, the said Robert William Thomson, have hereunto
set my hand and seal, this Twenty-first day of August, One thousand
eight hundred and sixty-three.