IMPROVEMENTS IN AIR ENGINES
Year: 1880

page_text: LETTERS PATENT to Benjamin Joseph Barnard Mills, of the Firm of Harris
and Mills, of 23, Southampton Buildings, in the County of Middlesex, Patent
Agent, for an Invention of "IMPROVEMENTS IN AIR ENGINES." A com-
munication from abroad by James Atkins Woodbury, Joshua Merrill, George
Patten, and Edward Franklin Woodbury, all of Boston, in the County of
Suffolk and State of Massachusetts, in the United States of America, all
Mechanical Engineers.
COMPLETE SPECIFICATION filed by the said Benjamin Joseph Barnard Mills
at the Office of the Commissioners of Patents on the 8th June 1880.
BENJAMIN JOSEPH BARNARD MILLS, of the Firm of Harris and Mills, of 23,
Southampton Buildings, in the County of Middlesex, Patent Agent. "IMPROVE-
MENTS IN AIR ENGINES." A communication from abroad by James Atkins
Woodbury, Joshua Merrill, George Patten, and Edward Franklin Woodbury, all
of Boston, in the County of Suffolk and State of Massachusetts, in the United
States of America, all Mechanical Engineers.
The Invention relates to that class of air engines which are operated by alternately
heating and cooling the same body of air over and over again, and to that particular
kind of such engines in which a working cylinder and piston are used in combina-
tion with a reverser, and has for its object the production of engines capable of
being operated by air at very high pressures, and also capable of heating and cooling
the air with very great rapidity.
It is a well known fact that the application of about 480 degrees of temperature
to atmospheric air in a confined state doubles its pressure, and it has been proved
by practical experiment that the same number of degrees of temperature applied to
air compressed to a pressure equal to two, four, or inore atmospheres doubles its
pressure as in the case of common atmospheric air.
It is also well known that a given amount of fuel applied to heating air developes
about four times the amount of mechanical force that the same amount of fuel
developes when applied to the generation of steam from water.
After a long series of practical experiments made by the inventors in working
air under high pressures, it has been found that it takes no more units of heat to
raise air compressed to a pressure equal to two, four, or more atmospheres to a

page_text: given temperature than it does to raise common atmospheric air to the same
temperature, and therefore it is obvious that there must be a great gain in operating
air engines with air at very high pressures.
The Invention consists in certain improvements in the construction and arrange-
ment of the parts, which will be readily understood by reference to the description
of the Drawings hereinafter given.
DESCRIPTION OF THE DRAWINGS.
Figure 1 is a plan of an Engine embodying the Invention; Figure 2 is a front
elevation Figure 3 is a rear elevation; Figure 4 is an end elevation; Figure 5 is
a vertical section on line 1, 1, on Figures 1 and 2; Figure 6 is a horizontal section
through one reverser and one working cylinder on line 2, 2, on Figure 5; Figure 7
is a partial vertical section of the working cylinder on line 1, 1, on Figures 1
and 2, enlarged; Figure 8 is a partial vertical section of the reverser cylinder and
the refrigerator on line 1, 1, on Figure 1, enlarged; Figure 9 is a horizontal section
through the working cylinder on line 5, 5, on Figure 5, enlarged; Figure 10 is a
partial vertical section of one side of the working cylinder on line 1, 1, on Figure 1,
enlarged; Figure 11 is a plan of the inner reverser cylinder; Figure 12 is an
elevation of said inner cylinder, with the regenerator plates attached thereto;
Figure 13 is a horizontal section through the reverser cylinder and regenerator
plates on line 3, 3, on Figure 12; Figure 14 is a detail of the governor connections
to the throttle valve; Figures 15 and 16 are respectively an inverted plan
and sectional elevation of a portion of the heater for the working cylinder;
Figures 17 and 18 are respectively an inverted plan and sectional elevation of a
portion of the heater attached to the reverser cylinder; Figures 19 and 20 are
respectively a plan and sectional elevation of a portion of the cooler; Figure 2] is
a. side elevation of the cylinders and beams of a modified form of engine, and
Figure 22 is a sectional elevation of the same, the cutting plane being through the
working cylinder on line 4, 4, on Figure 21.
Figures 1, 2, 3, 4, 5, 6, 21, and 22 are drawn to a scale of one twelfth full size.
Figures 7, 9, 11, 12, 13, and 14 are drawn one fourth full size, and Figures
8, 10, 15, 16, 17, 18, 19, 20, are drawn one half full size.
In the Drawings A and A¹ are two fire boxes or furnaces mounted upon the bed
plate B and provided with the grate a, ash pit C, fire door b, and ash pit door c, all
constructed in a well known manner.
The fire box casings A and A' extend to the rear of the combustion chamber
sufficiently far to serve as supports for the working cylinders D and D¹, the rear
portion being partially separated from the combustion chamber by the bridge
wall E, above which the products of combustion pass through the Hue E¹ across
the chamber F and thence escape into the chimney (not shown) through the
passage F'.
The working cylinders D and D¹ are cast open at both ends, and provided at
their lower ends with broad flanges d, the outer portions of which rest upon and
are securely bolted to the casings A and A', while to the inner portions of the same
flange of each cylinder is firmly bolted the disc or circular plate head G, in which are
set both ends of a series of U shaped pipes e, e, arranged as shown in Figures 15 and 16,
so that the body of each of said pipes depends from said plate into the chamber F,
and its two ends pass through the head G at different distances from its centre
and the centre or axis of the cylinder D or D'.
The lower portion of each of the cylinders D and D' is made of somewhat greater
diameter than the upper portion, and has fitted therein the short secondary cylinder
or shield f, the lower end of which rests upon the head G while its upper end is
provided with an outwardly projecting narrow flange or band f' which fits the
chambered portion of the cylinder D or D', said shield being made of such a length
that its upper end does not quite reach the shoulder g of the cylinder D or D
when its lower end rests on the head G to allow for unequal expansion, three or

page_text: more coiled metal springs g¹ being inserted between said shoulder g and the upper
end of said shield to insure contact between the lower end of said shield and the
head G as shown.
Between the shield fand its cylinder is an annular space the central portion
of which is made eccentric to said shield, as shown in Figure 9, into which one end
of each of the pipes e, e, opens, while the other end of each of said pipes opens into
the chamber beneath the piston H, the upper portion of which is fitted loosely to
the upper portion of its cylinder so as to be guided thereby in its upward and
downward movements, while its lower portion is reduced in diameter so as not to
touch the cylinder, as shown in Figure 5.
The upper ends of the cylinders D and D¹ are closed by the cylinder heads D°
and D³, each provided with an opening for the passage of the piston rod I, and two
cupped packing rings to prevent the escape of air around said rod, the upper end
of which is connected by the link J to one end of the beam K, or by a similar link
to the opposite end of said beam, which is also connected by its arm K' and the
rod K to the crank L upon the driving shaft L' mounted in bearings upon the
standards M, M, and having secured to its opposite end the crank L, and carrying
the driving pulley L³ as shown.
The beam K is also provided with a fourth arm K³ designed to be used for
driving a pump for raising water when desired, and also to serve as a counter
balance to arm K
The upper end of the piston H has mounted thereon two cupped leather packing
rings the outer edges of which are turned in opposite directions, said rings
being firmly secured to the piston so as to move with it by means of the metal
ring, and their cupped edges are kept in proper position and shape by the metal
ring interposed between the two leather rings i, j, in a well known manner.
metal packing may be used instead of the cupped leather rings if desired.
A
The beam K has its bearing upon the stand K supported by the cylinders D and
D₁, or said stand may extend downward to and be supported by the bed plate B.
N, N, are cylinders of the two reversers, each provided with a broad flange lat
its lower end, the outer portion of which rests upon and is firmly bolted to the
furnace casing A or A' in a position directly above the grate a, the lower end of
which cylinder is closed by the disc or circular head O, firmly bolted to the inner
portions of the flange l, and having set therein a series of U shaped pipes e¹ which
depend therefrom into the combustion chamber and are arranged relatively to each
other, as shown in Figures 17 and 18, and communicate through the head O with
two separate chambers, substantially as heretofore described in connection with the
heater attached to the working cylinder.
P is the reverser cylinder made of somewhat less diameter and placed within
and concentric with the cylinder N, with its lower end resting on the plate O in
such a manner as to form an annular chamber between the cylinders N and P to
serve as a regenerator.
The upper ends of the cylinders N and P are closed by the head Q, which is
firmly bolted to the cylinder N and rests upon a rubber packing ring m placed in
a groove in the upper end of the cylinder P to form an air tight joint, and allow
for unequal expansion.
The head Q has set therein and projecting upward therefrom a series of pipes n
bent into the form of an inverted U and arranged as shown in Figures 19 and 20,
one end of each of which communicates with the space between the cylinders N
and P, and the other end with the interior of the cylinder P above the reverser
piston R, and is also provided with the central upwardly projecting tubular bub Q
through which the piston rod R' passes, and to the upper end of which is secured
the upper end of the cooler' casing S, the lower end of which is firmly bolted
through the head Q to the cylinder N, thus forming a cooling chamber enclosing
the pipes n to be filled with cold water, as will be hereafter described.
The upper end of the piston rod R¹ is connected by the link T to the beam U
upon one side of the stand U', in which said beam has its bearings, while said beam
08001
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page_text: is connected upon the opposite side of said bearing by the link T¹ and piston rod
R to the reverser piston in the second reverser cylinder, which is constructed in all
respects like the one heretofore described.
The piston rods R1, R2, are each provided with two longitudinal passages n³, nº,
the lower ends of each of which open into a water chamber R³ formed in the upper
portion of the piston R, and the upper end of one passage communicates with the
Hexible pipe n leading therefrom to and connecting with the water discharge pipe
from the cooler, and the upper end of the other passage opens into the atmosphere
through pipe n³.
The pistons H and R are each cast in two parts and screwed together so as to
form hollow air tight chambers therein, the lower portion of each of which is filled
with fire brick, and the upper portion with asbestos, as shown in Figure 5.
The beam centre U2 has firmly secured to its outer end the pendent arm V
provided with the pin V¹, by means of which the beam U and the reverser pistons
may be worked by hand to start the engine, or by means of the hook connecting
rod W and the crank L² said beam and pistons may be worked by the power
exerted by the working pistons H, the hook end of the rod W engaging with the
handle or pin V', as shown in Figure 2.
V2 is a pendent arm hanging loosely from the beam centre U2 just outside of the
arm V, and having fitted to a socket in its lower end the rod m, the lower end of
which is pivotted to the hook connecting rod W, and provided with a detent notch
m with which an inwardly projecting tooth on the lower end of the spring mo
attached to the arm V2 engages to hold up the hook W when raised up to disengage
it from the pin V₁, a cam lever m² being pivotted to said spring as a means of
withdrawing said tooth from the notch when it is desired to drop the hook W onto
the pin V¹.
The reverser cylinder P has formed upon its upper end three or more outwardly
projecting lugs o, o, as shown in Figures 8 and 12, which rest upon shoulders
formed in the upper end of the cylinder N to support said cylinder P when the
cylinder head O is removed, and is provided near its lower end with a lateral
opening through an outwardly projecting boss p¹, the outer end of which fits
closely to the inner periphery of the cylinder N immediately around a corresponding
opening through the pipe q projecting horizontally from the rear of the cylinder N,
through which and the pipes q¹ and q' air may pass freely from the interior of the
reverser cylinder to the annular space in the working cylinder, and thence through
the pipes e, e, to the space beneath the working piston H, and vice versa, when the
throttle valve » is open.
The lower end of the cylinder P is also provided with two or more outwardly
projecting lugs p², p³, which co-operate with the boss p¹ to register the lower end
of said cylinder, and maintain it in its proper position within the cylinder N.
The fire grate a is provided with a downwardly projecting lug a¹, in which is.
formed a socket to receive the end of a lever a, shown in dotted lines in Figure 5,
by which the grate may be partially rotated about a vertical axis of motion for the
purpose of removing the ashes from the fire.
A throttle valve is placed in each of the pipes q, and mounted upon opposite
ends of a rocker shaft extending from one pipe to the other, and having secured
thereon a short lever 2, to the moveable end of which is connected one end of the
rod, the upper end of which is connected to one end of the lever pivotted to
the stand X, and connected at its other end with the vertically moving rod
the governor X in such a manner that a radial movement of the governor balls
shall move both of said valves about their axes, to open or close them according as
the speed of the engine is diminished or increased.
of
The lever may be used as a hand lever for the purpose of closing or partially
closing the throttle valves in opposition to the action of the governor, for the
purpose of slowing the engine.
In some cases a throttle valve actuated by a governor may be placed in a pipe
or passage way connecting the top and bottom' (or space above and below the

page_text: piston) of each working cylinder for the purpose of controlling the speed of the
engine, and another valve or cock operated or set by hand may be placed in
the said pipe in order to control or limit the sensibility of the governor's action.
By partially closing this latter valve or cock a too sudden passage of air from
below to above the piston may be controlled independent of the throttle worked by
the governor.
The space between the cylinders N and P is filled with a series of thin sheet
metal plates b² attached to the outer surface of the cylinder P by means of the
studs c¹ and screws c², the holes in each of said plates for the passage of the studs c¹
being slotted, as shown in Figure 12 to allow for unequal expansion.
The plates b are each provided with one or more vertically arranged ribs or
corrugations d' of slight projection, with broad plane surfaces d' at either side
thereof, said ribs serving the purpose of keeping said plane surfaces from coming
into close contact, and thus forming a series of very thin annular or segmental
passages, through which the air is compelled to pass from the heater to reach the
cooler, or vice versa, said plates being shown in Figures 8, 12, and 13, the number
and thickness of said plates and distances apart thereof being such as to give the
best results in rapid heating and cooling of the air.
D is an air pump provided with suitable valves and a plunger (not shown) to
which a vertical reciprocation is given by means of the connecting rod g² and the
wrist pin g³ set in the end of the beam U, said pump being arranged and adapted
to force air under pressure through the pipe h', check valve h2, and pipe h³ into the
working cylinders D and D¹ above their pistons H, and through pipes h* and check
valves 45 set therein into the reverser cylinder N, N.
F is a plunger circulating pump operated by the wrist pin set in the opposite
end of the beam U, acting through the connecting rod F3, and adapted to force
water through the pipes and j' into the interior of the cooling casings S, S, thence
through pipes k2 and 3 into the annular chambers and surrounding the upper
ends of the reverser cylinders N, N, to prevent the transmission of heat to the
cooler Q, n, S, and thence through pipes m' and m² to the annular chamber n'
and n surrounding the working cylinder D and D₁ respectively near the middle of
their height or at points below the lowest position to which the packing rings j, j,
on the upper ends of the piston H descend to prevent heating the upper portions
of the cylinders D and D¹ to such an extent as to injure the packing j, j, the water
being finally discharged from the chambers n' and n through the pipes o' and o³
into any convenient receptacle (not shown).
Water is also forced through the flexible pipe n', passage no, in the piston rod
R¹ or R² to the chamber R³ in the piston R, and thence through passage n6 in
the piston rod R' or R2 and discharged through pipe n into any convenient
receptacle.
The piston rod R' is packed by cupped leather packing rings p³ secured to the
upper end of the hub Q₁ of the cylinder head Q, as shown.
The heater and cooler pipes instead of being bent to a U shape may be straight
pipes with their lower ends connected by half turn junctions or an annular pipe, if
desired, without departing from the principles of the Invention, but the U shaped
pipes are preferred as being best the construction all things considered.
The operation of the Invention is as follows:-The cranks L and L* being set so
that the crank L² leads the crank L, in regard to the effect produced upon the
respective pistons operated thereby, from seventy to ninety degrees, supposing the
crank shaft to be revolved in the direction indicated by the arrow on Figures 2
and 3, if a fire be built upon the grate a so as to heat the air in the heater pipes
c and e', to start the engine the operator disengages the book rod W from the
pin V and, by means of the handle of said pin P₁, works the beam U by hand
through an arc limited by the stops t, t, and thereby moves the reversing pistons
alternately up and down in their respective cylinders, the effect of which is that
the pistons in the reverser cylinders displace the air contained therein by driving
the air in the cold end of one of the said cylinders down through the tubes n and

page_text: the regenerator space into the tubes e¹, and driving the air in the hot end of the
other reverser cylinder through the tubes c¹ and the regenerator space into the tubes
n, thereby greatly increasing the pressure in one reverser cylinder and in the lower
end of one working cylinder, and correspondingly diminishing the pressure in the
other reverser cylinder and the lower end of the other working cylinder with
which it communicates, while no change in the pressure above the working pistons
takes place, the effect of which is that the increase of pressure beneath one of the
working pistons causes it to be moved upward till it reaches the extreme of its
upward stroke, when the reverser pistons are made to change their positions by
hand, thereby diminishing the pressure beneath the working piston which has just
completed its upward stroke and increasing it beneath the one that has just
completed its downward stroke, thus creating a differential pressure beneath the
two working pistons, by means of which the engine is set in motion, the pressure
alternately changing from one cylinder to the other, when the book W is allowed to
engage with the pin V', and the reverser pistons will then continue to be worked
by the power of the working pistons, and the air pump and the water circulating
pump will be set in motion and made to perform their respective offices of forcing
air into the upper ends of the working cylinders under pressure, and circu-
lating cold water around and through certain parts of the engine to keep such
parts cool.
As air is pumped into the engine the pressure is increased therein by compressing
the air throughout all the air chambers and passages, but the air in the working
cylinders above their respective pistons not being effected sensibly by the heat from
the furnaces remains substantially at its normal pressure, and as the two chambers
above said pistons are connected by the pipe 3, through which the air contained
in said chambers may pass freely in either direction as one piston ascends and the
other descends, and as the aggregate of the cubical contents of the two chambers is
at all times substantially the same in whatever positions the pistons may be placed,
it follows that there will be no material change in the pressure in said chambers,
except such as is due to the compression of the air by pumping in more air, and
this being understood it will be equally clear that the power of the engine will be
determined by the difference in the pressure alternately created in the reverser
cylinders by the movements of their pistons heating the air in one reverser cylinder
and cooling it in the other, thereby at each stroke of the engine increasing the
pressure beneath one working piston and diminishing it beneath the other working
piston.
With the cranks adjusted to give the proper lead, and the beams in the position
shown in the Drawings, the piston in the working cylinder D will be at the centre
of its upward movement, and the piston in the working cylinder D¹ will be at the
centre of its downward movement, while the piston which works in the reverser
cylinder, which is in direct communication with the lower end of the cylinder D,
has not quite reached the extreme of its upward stroke, and the other reverser piston
has not quite reached the extreme of its downward stroke.
The downward stroke of the reverser piston forces the hot air beneath it through
the tubes e¹, through the regenerator space among the plates b*, which extract a
Jarge proportion of the heat from the air as it passes, and through the tubes n,
which are surrounded by cold water, as before described, into the space above said
piston, thereby reducing the pressure beneath the piston of the working cylinder,
which has just completed its upward stroke, while at the same time the other
reverser piston by its upward motion is forcing the cold air above it through the
pipes n, through the regenerator, where it takes up a large amount of heat from
the plates be, through the pipes e', where it is heated, through the lower part of the
cylinder P, pipes q, q', and q, and e, when it is still further heated, and discharged
into the space beneath the piston in the working cylinder to exert its power, due
to the increase of pressure caused by the rise in temperature, upon said piston to
move it upwards.
This operation is repeated as long as power is desired to be used, the increase of

page_text: pressure and consequent developement of power alternating from one working
cylinder to the other, each of said working pistons being controlled by its own
reverser piston, as above described, and by the throttle valve in the pipe q and the
governor connected therewith.
In Figures 21 and 22 is illustrated a modified form of the engine, having one
double acting working cylinder and two reversers, the heated end of one of said
reversers being connected by the pipes q, q', q², to the lower end of the working
cylinder, and the heated end of the other reverser being converted by the pipes q
and q with the upper end of the working cylinder in such a manner that heated
air is alternately admitted to the working cylinder upon opposite sides of its
piston.
In the modification here shown an annular chamber o* is formed in the upper
head of the working cylinder, in close proximity to the packing surrounding the
piston rod I, for the purpose of preventing injury to the packing by the heated air
in the chamber above the piston H.
The working cylinder is made in two parts of about equal lengths, and has
interposed between them two cupped packing rings o" and o", and the metal ring o',
all arranged and secured in position before bolting said two parts of said cylinder
together, with the cupped portions of the packing rings turned in opposite directions,
all as shown in Figure 22.
Each part of the working cylinder has formed therein, in close proximity to the
packing rings o and of, an annular water chamber, os or 0%, through which water
circulates to prevent the transmission of heat to the packing from either end of the
cylinder.
A modified form of the engine may be constructed by employing two reversers
and two double acting working cylinders, each such working cylinder being
constructed in a similar manner to that of the modification shown at Figures
21 and 22, where only one double acting working cylinder and two reversers are
shown. In this modification connections must be made by pipes or otherwise so
that the heated end of each reverser is connected with both the lower end or
space beneath the piston of one working cylinder and the upper end or space
above the piston of the other working cylinder. This modified form would have
the advantage over the form described, in which two reversers and two single
acting working cylinders are combined, that for exorting the same power working
cylinders of lesser diameter having only half the area of single acting cylinders
may be employed.
Another modified form of the engine may be constructed by employing only one
reverser and only one single acting working cylinder, thus being similar to the engine
shown in the Drawings with two reversers and two single acting working cylinders
if one reverser and its working cylinder were removed. Such an engine would,
without further addition, exert its power only during the upward stroke of the
piston, and would be applicable in such cases where one sided action only is
required, for instance, for driving a single acting pit pump; this form could for
other purposes be further modified by applying a counterbalance of such weight.
that one half the power exerted in the upward stroke of the engine would be
employed to raise this same weight, which in the downward stroke of the piston
would react or give back the half of the power employed to raise it; thus this
modification would in reality be acting in both directions, giving regular and
and uninterrupted power, that is to say, one half each way. Instead of weights or
counterbalances the space above the piston could be made of the proper capacity
either by itself or by connection with a suitable chamber to form an air vessel, in
which, by the upward stroke of the piston the air would be so compressed as to
require one half of the power exerted in that upward stroke to compress it, whilst
during the downward stroke this compressed air would react like a spring and
give back that one half of the power, and thus the engine work regularly and
without interruption of force, one half being virtually exerted for useful effect in
the upward stroke by the excess of power in the heated air over and above the

page_text: power required to compress the air above the piston, and equal force being exerted
in the downward stroke for useful effect by the expansion of the compressed air or
air spring. Such an engine with but one reverser and one single acting working
cylinder would be comparatively very simple and cheap.
To heat the air rapidly is one of the main requirements of a successful air engine.
Heaters or heating apparatus to do this effectively must combine the properties of
the greatest possible heating surface with the least possible contents of air, the air
being subdivided as much as possible within such heaters. Of this nature are the
heaters shown in the Drawings and described in the Specification. Now all such
heaters are liable to rapid injury and destruction by the influence of the heat and
oxidation by the fire gases on the one side, and the rapid passage of the hot air on the
other. It is therefore important that a metal should be used in their construction
which will combine the greatest possible resistance to the heat and oxidation, with
a cost not too high to preclude its employment. Nickel has been found to meet
these requirements.
Having thus described the nature of the said Invention and the mode in which
the saine is carried into effect, I would have it understood that what I claim is,-
First. In an air engine, a heater composed of a series of tubes set in the cylinder
head in a position to be acted upon by the hot gases from the furnace or other
means of applying heat, and through which air may be circulated by the move-
ments of the reverser piston, substantially as described.
Second. In an air engine to be operated by alternately heating and cooling the
same body of air, a cooler composed of a series of tubes set in the cylinder head,
and through which air may be circulated by the movements of the reverser piston,
in combination with an enclosing casing surrounding said tubes and adapted to be
filled with water, substantially as described.
Third. In an air engine to be operated by alternately heating and cooling the
same body of air, a heater and cooler, each composed of a series of tubes set in
the cylinder heads, in combination with a reverser piston adapted to move the air
through said tubes, substantially as described.
Fourth. In an air engine to be operated by alternately heating and cooling the
same body of air, a heater or cooler, one or both composed of a series of U shaped
tubes or their equivalents, both ends of each of which are set in and communicate
through the cylinder head or heads, substantially as described.
Fifth. In an air engine the combination of the cylinders N and P, arranged one
within the other with an annular space between them, and having their ends
closed by suitable heads; a heater or cooler, one or both composed of a series
of U shaped tubes or their equivalents set in said head or heads, when one end of
each of such tubes communicates with the interior of the cylinder P and the other
end of each of said tubes communicates with the annular space between said
cylinders, and a reverser piston adapted to move the air alternately in opposite
directions through said tubes, substantially as described.
Sixth. The cylinder N closed at its two ends by the heads and Q in com-
bination with the inner cylinder P resting upon the head O, and pressed thereto by
a spring or elastic material m placed between its upper end and the head Q,
substantially as described.
Seventh. In combination with the cylinder N closed at its ends by the heads O
and Q the cylinder P made slightly shorter than the cylinder N, and placed therein
and concentric therewith, and a packing of rubber or other suitable elastic material
placed between the upper end of said cylinder P and the underside of the plate or
head Q, and resting in an annular groove formed in the upper end of said cylinder
P, substantially as described.
Eighth. In combination with a working cylinder and a reverser composed of
two cylinders placed one within the other with an annular space between them
the short pipe p, p, projecting from the side of the inner cylinder, and bridging
the annular space between the cylinders, and a pipe leading therefrom to the
working cylinder, substantially as described.

page_text: Ninth. In an air engine the combination of a working cylinder and a reverser
cylinder connected by a pipe for the passage of air from one to the other, a throttle
valve placed in said pipe, and a governor connected to and adapted to move said
throttle valve to control the speed of the engine, all arranged for operation sub-
stantially as described.
Tenth. In combination with a working cylinder and a reverser cylinder con-
nected by an air passage a throttle valve placed in said passage, a governor
connected with and adapted to operate said throttle, and a hand lever adapted to
close said throttle against the resistance of the governor, substantially as
described.
Eleventh. In an air engine having two working cylinders and two reversers
arranged in pairs two throttle valves placed upon the same shaft, and a governor
connected to and adapted to partially rotate said shaft, and thus open or close both
of said throttle valves at the same time, substantially as described.
Twelfth. In air engines of the character herein described connecting the top and
bottom (or space above and below the piston) of each working cylinder with a
pipe or passage way, in which is placed a throttle valve actuated by a governor,
and a valve or cock worked or set by hand, for the purposes described.
Thirteenth. In combination with a working cylinder chambered at its lower end
the shield fitted to said cylinder with an annular space between it and the
chambered portion of said cylinder, and supported upon the cylinder head G,
substantially as described.
Fourteenth. The combination of the working cylinder D or D' chambered, as
set forth, and provided with the head C, the shield or inner cylinder f fitted thereto
with an annular space between it and the chambered portion of the cylinder and
the springs gl, all arranged and adapted to operate substantially as and for the
purpose described.
Fifteenth. In a hot air engine the combination of a working cylinder, a long
piston adapted to be worked under pressure upon both sides thereof, and packing
rings secured to and moving with said piston, and adapted to resist said pressure in
both directions, substantially as described.
Sixteenth. The regenerator plates 62 provided
ribs or corrugations with broad plane surfaces
bination with the cylinders N and P and air
stantially as described.
with slightly projecting vertical
between them when used in com-
heating and cooling devices, sub-
Seventeenth. In combination with the cylinders N and P arranged as set forth
the regenerator plates be secured to the exterior of the cylinder P, substantially as
described.
Eighteenth. The combination of a single acting working cylinder provided with
a piston, and containing air under pressure upon both sides of said piston, a
reverser cylinder, means of applying heat to the lower end of the reverser, and
means of conveying air from the heated end of the reverser to one end of the
working cylinder while the air in the other end of the working cylinder remains
at its normal temperature, substantially as and for the purpose described.
Nineteenth. The combination of a working cylinder provided with a piston, and
adapted to contain air under pressure upon both sides of said piston, and to be
worked by alternately heating and cooling the air upon one side of said piston,
while the air upon the other side of said piston remains at its normal temperature,
a reverser cylinder, and a furnace or other means of applying heat to the working
cylinder and reverser, substantially as described.
Twentieth. The combination of a working cylinder provided with a long piston
adapted to be worked by alternately heating and cooling the air upon one side of
said piston, while the air upon the other side of said piston remains at its normal
temperature, a reverser cylinder, and a furnace or other means of applying heat to
the working cylinder and reverser, substantially as described.
Twenty first. The combination of a reverser cylinder, a working cylinder, a

page_text: pump for forcing air into said cylinders under pressure, and a furnace or other
means of applying heat to one end of said cylinders, while the air in the other
end of the working cylinder remains at or near its normal temperature, substan-
tially as described.
Twenty second. In combination with a reverser cylinder provided with a heater
and a regenerator a pipe or passage leading from the heated portion of the reverser
cylinder to the working cylinder, substantially as described.
Twenty third. The use of nickel in the construction of the heating apparatus of
air engines, as and for the purpose described.
Twenty fourth. The outer casing of the reverser or working cylinder furnace
made in two or more parts, divided in such a manner that one portion may be
removed to give access to the heater, and allow it to be removed without disturbing
the other parts of the engine, substantially as described.
Twenty fifth. In combination with a regenerator of an air engine a water space
surrounding a portion of the upper part of said regenerator, substantially as and
for the purposes described.
Twenty sixth. In combination with a reverser cylinder provided with a heater
and a regenerator a pipe or passage leading from the heated end of said cylinder
to the working cylinder, and a pump adapted to force air into said reverser cylinder
under pressure, substantially as described.
Twenty seventh. In combination with a reverser cylinder provided with a
regenerator and a refrigerator a heater provided with a series of passages leading
from the beated end of the reverser cylinder to the regenerator, and adapted to
subdivide the column of air moved by the reverser piston into a series of smaller
columns, substantially as described.
Twenty eighth. The combination of two reverser cylinders, each provided with
a furnace or other means of applying heat thereto, and two single acting working
cylinders, all arranged and adapted to operate substantially as described.
Twenty ninth. The combination of two single acting working cylinders having
the spaces above their pistons connected by a pipe or passage, two reverser cylinders
having direct communication with the spaces beneath the working pistons, and a
furnace or other means of applying heat to the reversers or working cylinders,
substantially as described.
Thirtieth. The combination of two working cylinders and two reverser cylinders
with a furnace or other means of applying heat to all of said cylinders, substantially
as and for the purposes set forth.
Thirty first. In combination with two working cylinders provided with pistons
and adapted to be charged with compressed air upon both sides of said pistons, and
to be operated by alternately heating and cooling the compressed air upon one side
only of each of said pistons, a pipe or passage connecting the chambers in the cool
ends of said cylinders, substantially as and for the purposes described.
Thirty second. The combination in an air engine of two working cylinders
provided with pistons connected to opposite ends of a vibrating beam, and two
reverser pistons adapted to alternately change the air from a heating chamber to a
cooling chamber, and vice versa, substantially as described.
Thirty third. The combination of two reverser cylinders and a double acting
working cylinder provided with a long piston, with a furnace or other means of
applying heat to each of said cylinders, substantially as described.
Thirty fourth. The combination of two reverser cylinders and two double acting
working cylinders, each of such double acting working cylinders being con-
structed in a similar manner to those of the modification represented at Figures
21 and 22, all arranged and adapted to operate substantially as described.
Thirty fifth. The combination of one reverser and one single acting working
cylinder, similar to those of the engine shown in the Drawings, with two reversers
and two single acting working cylinders, arranged and adapted to operate sub-
stantially as described,

page_text: Thirty sixth. In a double acting working cylinder operated by hot air upon each
side of the piston a water space in close proximity to the packing of the piston
rod, substantially as and for the purposes described.
Thirty seventh. In combination with a double acting working cylinder of a
hot air engine provided with a long piston a packing for said piston located at
or near the centre of the length of said cylinder, substantially as and for the
purposes described.
Thirty eighth. In combination with a double acting working cylinder provided
with a piston actuated by hot air applied to each end thereof a packing for said
piston located at or near the centre of the length of said cylinder, and an annular
water space upon each side of said packing, substantially as and for the purposes
described.
Thirty ninth. In combination with a double acting working cylinder provided
with a long piston and two reverser cylinders a pipe or passage leading from the
hot end of one of said reverser cylinders to the lower end of the working cylinder,
and a pipe or passage leading from the hot end of the other reverser cylinder to
the upper end of the working cylinders, substantially as and for the purposes
described.
In witness whereof, I, the said Benjamin Joseph Barnard Mills, have here-
unto set my hand and seal, this Twenty eighth day of April, in the year
of our Lord One thousand eight hundred and eighty.