IMPROVEMENTS IN THE MEANS AND APPARATUS EMPLOYED FOR CONVEYING TELEGRAPHIC DISPATCHES, LETTERS, AND OTHER LIGHT ARTICLES THROUGH TUBES
Year: 1867

page_text: LETTERS PATENT to Charles William Siemens, of No. 8, Great George
Street, Westminster, in the County of Middlesex, for the Invention of
"IMPROVEMENTS IN THE MEANS AND APPARATUS EMPLOYED FOR CONVEYING
TELEGRAPHIC DISPATCHES, LETTERS, AND OTHER LIGHT ARTICLES THROUGH
TUBES."-Partly a communication from abroad by Dr. Werner Siemens,
of Berlin, in the Kingdom of Prussia.
Sealed the 22nd November 1867, and dated the 23rd May 1867.
PROVISIONAL SPECIFICATION left by the said Charles William Siemens'
at the Office of the Commissioners of Patents, with his Petition, on the
23rd May 1867.
I, CHARLES WILLIAM SIEMENS, of No. 8, Great George Street, Westminster,
in the County of Middlesex, do hereby declare the nature of the said Invention
for "IMPROVEMENTS IN THE MEANS AND APPARATUS EMPLOYED FOR CONVEYING
TELEGRAPHIC DISPATCHES, LETTERS, AND OTHER LIGHT ARTICLES THROUGH TUBES,"
to be as follows:-
In the arrangements heretofore employed for conveying letters or parcels
through pneumatic tubes from one station to another the one end of the tube'
has been made to communicate with the one station, and the other end has
been made to communicate with the other station, and the letters or parcels

page_text: have been conveyed through the tube inside pistons or cylindrical carriages
caused to travel along the tube either by exhausting the air from the tube in
front of the piston, or by forcing air into the tube behind the piston, or by both
methods combined.
By the present Invention pneumatic tubes are so arranged as to have no
terminal points, but to form closed pneumatic circuits communicating at one
point (a central station) with an air pump which causes the air to travel
round and round in the tube continually in the same direction, so that on in-
troducing a piston or cylindrical carriage containing the dispatches into the tube
at such pumping station it would, if not intercepted at an intermediate point,
be caused to travel right round the circuit, and thus eventually arrive at the
pumping station again. At intermediate points in the pneumatic circuit
thus established are situated the stations to or from which dispatches are to be
conveyed from or to the central or pumping station. For conveying dispatches
from these intermediate stations to the central station, or vice versa, they are
made to communicate with the circuit by means of a branch pipe, into the
one end of which the piston is introduced, and whence, after closing the said
end thereof, and then establishing a communication at the other end with the
circuit, the piston is made to pass into the circuit, where it is propelled by
the circulating air; so as to arrive at the central station. For receiving
dispatches oi parcels from the circuit into the stations a portion of the
tube forming the circuit is arranged similar to a switch on railways,
that is, at one point it is capable of being moved away from the circuit
and made to communicate, with a closed chamber into which the piston
or cylindrical carriage containing the dispatches destined for the particular
station is consequently caused to pass from the circuit, its momentum being
gradually absorbed in such chamber by a series of brushes arranged longi
tudinally so as to produce a powerful drag upon the piston; or such retardation
may be effected by causing the piston to compress the air in front of it in the
chamber, in the end of which a small hole is made so as to allow the com-
pressed air to escape in order to prevent rebound. This chamber is closed, at
the sides and end, and is provided, with a door opening on hinges for removing
the dispatches or parcels therefrom. While the circuit or main tube is thus
directed into the receiving apparatus the circulation of air in the same never-
theless continues through a "by pass" branching from the main tube at each
intermediate station, immediately in front of and behind the moveable.or
"switch" point. The before-mentioned branch for dispatching the parcels
from the stations is by preference so arranged that when the main tube is
diverted at one point into the receiving chamber, thus leaving an opening in

page_text: the main tube at that point, such dispatching branch is simultaneously moved
in front of the opening in the main tube, whereupon, owing to the branch
being placed in an inclined position, the piston or cylindrical carriage that
has previously been placed in such branch passes down into the main tube by
gravity, and is then urged forward by the circulating current of air. When
the pneumatic circuit is of considerable extent and the tube is of small:
diameter the speed of transit of the the pistons may be considerably increased
by the employment of bydrogen or light carburetted hydrogen gas.in the tube
in place of atmospheric air, which gas might be supplied continually at the
pumping station to make up for losses through leakage, and to prevent such
leakage the maximum pressure in the tube may be made never to exceed that
of the external atmosphere, which may also be preferable even when atmos
spheric air is used. In introducing fresh air or gases into the tube to make
up for leakage such air or gases are by preference first made to pass through a
drying chamber containing dry lime or other substances.that will take up the
moisture from the air or gas before it enters the tube. As a number. of the
pistons or cylindrical carriages may require to be continually dispatched from:
the central station to the several intermediate stations on the circuit information.
is conveyed to the particular station for which a certain carriage is destined
by means either of an electric telegraph signal which is given at the central
station at the time when the carriage is introduced, and by causing the said
signal to set in motion a clockwork mechanism at the said station a second
signal may thereby be given after a lapse of time corresponding with the time
the carriage takes to travel from the central station to the intermediate station
in question, thereby warning the attendant of the proper moment when he has
to divert the main pipe into the receiving chamber; or the carriages may be
dispatched at preconcerted intervals of time to the respective stations, where
electric clocks are made to indicate to the attendants the exact time when
they have to expect a carriage; or the attendant at any one intermediate
station may be guided as to the precise moment when to move the tube for
the reception of a message by means of the vibration produced in the tube itself
by the approaching carriage. In order to render these vibrations sensible at
the station the tube may be laid hollow upon supports for a certain distance
before the station, and a signal may be received either by the transmission of
sound through the tube only or by means of a pendulum ball so suspended as
to touch the tube with a contact point opposite, through which a galvanic
circuit including an alarum can be brought into action the moment the
vibratory motion of the tube causes the pendulum to rebound upon the contact
noint
.

page_text: A number of the before-described pneumatic circuits may be made to
communicate with one central station, and in large towns one or more of the
intermediate stations on any circuit may be constituted a branch central
station, from which again a series of pneumatic circuits may branch out.
At stations where carriages come in at very frequent intervals two or more
receiving chambers may be provided, into which successive pistons may be
"switched" in rotation to allow time for their removal.
The carriages employed for transmitting the dispatches or parcels are by
preference made cylindrical in form, and are so arranged that they can be
opened for the introduction of dispatches, letters, or parcels, and they are
provided in front and behind with a pair of .wheels at right angles to each
other, each wheel being nearly of the internal diameter of the tube itself.
The body of the piston or cylinder need not touch the internal surface. of the
tube, because the friction produced by the wheels is so slight as to ronder a
close fit not necessary.
It will be readily understood that in working pneumatic circuits on the
above-described principle a great number of pistons may be travelling within
the tube at the same time, both coming to and going from the central and
intermediate stations, thus rendering this system capable of forwarding a great
number of dispatches or parcels at frequent intervals without its being for this
purpose necessary to attain a high rate of speed of transit.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Charles William Siemens in the Great Seal Patent Office on
the 23rd November 1867.
TO ALL TO WHOM THESE PRESENTS. SHALL COME, I, CHARLES
WILLIAM SIEMENS, of No. 3, Great George Street, Westminster, in the County
of Middlesex, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-third day of May, in the year of our Lord One
thousand eight hundred and sixty-seven, in the thirtieth year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto me, the said
Charles William Siemens, Her special licence that I, the said Charles William
Siemens, my executors, administrators, and assigns, or such others as I, the
said Charles William Siemens, my executors, administrators, and assigns,
should at any time agree with, and no others, from time to time and at all
times thereafter during the term therein expressed, should and lawfully might

page_text: make, use, exercise, and vend, within the United Kingdom of Great Britain
and Ireland, the Channel Islands, and Isle of Man, an Invention for "IMPROVE-
MENTS IN THE MEANS AND APPARATUS EMPLOYED FOR CONVEYING TELEGRAPHIC
DISPATCHES, LETTERS, AND OTHER LIGHT ARTICLES THROUGH TUBES," partly the
result of a communication made to me from abroad by Dr. Werner Siemens,
of Berlin, in the Kingdom of Prussia, and partly of an Invention and discovery
made by myself, upon the condition (amongst others) that I, the said Charles
William Siemens, my executors or administrators, by an instrument in writing
under my, or their, or one of their hands and seals, should particularly describe
and ascertain the nature of the said Invention, and in what manner the same
was to be performed, and cause the same to be filed in the Great Seal
Patent Office within six calendar months next and immediately after the date
of the said Letters Patent.
NOW KNOW YE, that I, the said Charles William Siemens, do hereby
declare the nature of the said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by the
following statement thereof, reference being had to the accompanying Drawings,
and to the figures and letters marked thereon, that is to say :—
In the arrangements heretofore employed for conveying letters or parcels
through pneumatic tubes from one station to another, the one end of the tube
has been made to communicate with the one station and the other end has
been made to communicate with the other station, and the letters or parcels
have been conveyed through the tube inside pistons or cylindrical carriages
caused to travel along the tube either by exhausting the air from the tube
in front of the piston, or by foreing air into the tube behind the piston,
or by both methods combined. Such tubes have been made of comparatively
large diameter in order to provide sufficient room in the carriages for con-
taining the letters and parcels to be forwarded, thus entailing both a great
outlay in establishing the system of tubes, as also the erection of large
pumping engines for producing the required pressure for propelling the
carriages, in addition to which a loss of the propelling power was occasioned.
both by the leakage of the air past the carriages when these did not fit. the
tube completely, and from the fact that when a carriage arrived at the end
station the air constituting the propelling medium must of necessity escape
into the atmosphere.
Now the present Invention has for its object to obviate. these defects by the
establishment of a system of pneumatic tubes of comparatively small diameter,
and consequently of an inexpensive nature, so arranged that while the carriages

page_text: or pistons travelling in the same are of correspondingly small dimensions, and
consequently require no great power to propel them, the smallness of the capacity.
of these carriages is compensated for by the rapidity with which they may be.
dispatched in quick succession from one station to another, while practically no
loss of propelling power from the before-mentioned causes can take place. For
this purpose the system of pueumatic tubes is so arranged as to have no
terminal points, but to form one or more closed pneumatic circuits, constructed
by preference of light wrought-iron tubes of small diameter fixed together by
flanged joints, and communicating at one point (a central station) with an air
pump, which causes the air to travel round and round in the circuit continually
in the same direction, so that on introducing a piston or cylindrical carriage
containing the dispatches into the tube at such pumping station it would if not
intercepted at an intermediate point be caused to travel right round the circuit
and thus eventually arrive at the pumping station again. At intermediate points
in the pneumatic circuit thus established åre situated the stations to or from
which dispatches are to be conveyed from or to the central or pumping
station; thus, for instance, at Figure 1 on Sheet I. of the accompanying
Drawings is shown a diagram of three such closed circuits A, B, C, all
communicating with the central pumping station D, the pump at which causes
the air to travel continually round in each circuit in the direction of the
arrows.. Upon the circuit A: are established three intermediate stations 1, 2, 3,
on the circuit B are four such stations, and on the circuit C are seven stations.
The carriages containing; the letters, dispatches, or other light objects to be
forwarded are introduced into the circuits at the central station D, and are
carried forward in the same in the direction of the arrows by the circulating
air. If the carriage introduced at D into circuit C is destined for the station
1, it is there intercepted in its course and removed from the circuit; if, on the
other hand, it is intended for station 7, it is allowed to pass all the intermediate
stations and is only intercepted at that point; if, on the other hand, a carriage
is to be conveyed from the station 1 to the central station D, it is also caused
on being introduced into the circuit at that point to travel all round the
circuit in the direction of the arrows, passing all the intermediate stations
2 to 7 until it arrives at D. Carriages containing the dispatches and other
articles may conveniently be forwarded at certain fixed intervals of time from
each of the intermediate stations upon one circuit to the central station, where
they are sorted and dispatched to the local stations upon the same or other
circuits for which they are intended, thus a dispatch letter dropped into the
receiving box of station 2, circuit A, and intended for station 4 on circuit C,

page_text: would proceed in the first place to the central station, where it would be,
placed with other letters or small parcels into the carriage intended for station 4
on circuit C. Upon its arrival at such station the contents of the carriage
would be handed to one or more carriers to be conveyed to their destination;
also, if required, carriages may be forwarded from one intermediate station to
another on the same circuit by being introduced into the circuit at the one
station and intercepted at the other. For receiving dispatches or parcels
from the circuit into the stations, a portion of the tube forming the circuit is.
arranged similar to a "switch" on railways, that is, at one point it is capable
of being moved away from the circuit and made to communicate with a closed.
chamber, iuto which the piston or cylindrical carriage containing the dispatches
destined for the particular station is consequently caused to pass from the
circuit, its momentum being gradually absorbed in such chamber, by a series
of brushes or projecting pieces of india-rubber or leather, arranged longitudinally,
so as to produce a powerful drag upon the piston, the closed end of the
chamber being provided with a buffer or spring of india-rubber or other
suitable material for the carriage to strike against; or the retardation may be
effected by causing the carriage or piston to compress the air in front of it in
the chamber, in the end of which.a small hole is made so as to allow the
compressed air to escape in order.to prevent rebound, an annular buffer spring.
being also in this case provided for the carriage to strike against. This
chamber is closed at the sides.and end, and is provided either with a door
opening on hinges for removing the carriage containing the dispatches or
parcels therefrom, or the carriage may be pushed out of the chamber by means.
of a rod inserted through the hole in the end of the latter. While the circuit
tube is thus directed at any one station into the receiving apparatus. the
circulation of the air in the same nevertheless continues through. a "by-pass "";"
or pipe branching from the main tube at each intermediate station immediately.
in front of and behind the the moveable or "switch." part. For conveying dis-
patches from the intermediate stations to the central station they are made
to communicate with the circuit by means of a branch pipe, into the one end
of which the piston is introduced, and whence, after closing the said end
thereof, and then establishing a communication at the other end, with the
circuit, the piston is made to pass into the circuit, where it is propelled by,
the circulating air so as to arrive at the central station. This branch for
dispatching. the parcels from the stations is by preference. so combined with
the moveable part or "switch" of the main tube, that when this is diverted
into the receiving chamber, thus leaving an opening in the main tube at the
point of separation, such dispatching branch is simultaneously moved in front

page_text: of the opening in the main tube, whereupon owing to the branch being placeil
in an inclined position the piston or cylindrical carriage that has previously
been placed in such branch passes down into the main tube by gravity, and
is then urged forward by the circulating current of air.
.At Figure 2 of the Drawings is shewn the before described arrangement
for receiving and dispatching the carriages at the intermediate stations,
together with the "by-pass" for keeping up the circulation of the air in the
circuit. A, A, are portions of the tube forming the pneumatic circuit, and A¹
is the moveable part or "switch" thereof; this is connected to the tube A
at one end by a flexible air-tight joint E, while the other end is carried in a
slide F, fitting in a more or less perfectly air-tight manner against the curved
surface of the block G in which the other part of the tube A is fixed. In
this block is also fixed the open end of the receiving chamber H, the other
end of which is closed and is provided with buffer springs I, while a small hole J
is formed in the end to allow of the escape of the air as the carriage passes
in, as before mentioned. The slide F carries furthermore the open. end of
the dispatching branch K, the other end of which is closed by a sliding cover
at L. The slide is connected to the toggle joint lever M, which is actuated
by the handle N so as to move the switch A¹ and dispatching branch K
simultaneously either into the position shown in full lines or into that shewn
in dotted lines. When in the latter position the switch tube A is in a line
with the circuit tube A, in which position it will allow any carriage or piston
approaching the station in the direction of the arrows to pass the same on
its way to another station; when, on the other hand, the carriage is
to be received into the station the switch is moved into the position shewn in
full lines in front of the receiving chamber H, and the carriage passes from
the former into the latter; at the same time the dispatching tube K is
moved in front of the open end of the tube A, and any carriage that has
previously been placed in it for conveyance to the central or other station
consequently passes into the tube A and is conveyed along the circuit, the
current of air in which is maintained while the switch. tube is thus diverted
from it by means of the "by-pass "O, this being a tube communicating
with the circuit at P and Q, so that the current of air passes uninterruptedly
through the same from the part of the tube A just behind the switch to the
other part beyond the switch, as indicated by the arrows. The communication
between the "by-pass" and the tube. A is by preference established by
forming a portion of the tube A with perforations, as shewn, enclosing which
in an air-tight manner is the casing P and Q, thus forming an annular space
round the tube with which the "by-pass "O communicates.

page_text: Figure 3 shews a diagram of the arrangement which I prefer to employ
for dispatching the carriages from the central station to the intermediate
stations of three different circuits in connection therewith, as indicated at
Figure 1, and for receiving the carriages from the stations on such circuits
into the central station, as also the mode in which the circulation of the air
may be effected in the three circuits simultaneously by one and the same
pumping engine. A, A, B, B, C, C¹, are the three circuit tubes com-
uunicating on the one side with the dispatching chambers K', K; K³, and
on the other side with the receiving chambers H1, H2, H³. Each of the
tubes A, B, C, is formed with perforations at points a, a, b, b¹, c; c', just in
front of the receiving and dispatching chambers, which perforated portions
are enclosed in air-tight casings R, R¹, S, S', T, T', communicating with the
pipes U, U. Each of these pipes opens into an air chamber V, V¹, of
sufficient capacity to equalize the flow of the air through the tubes, which
air chambers are put in communication by means of the pipes W, W¹, with
any suitable construction of air pump X, worked by a steam engine Y,
or other available source of motive power. The pump is by preference
surrounded by a casing or chamber, not shewn, through which cold water is
made to circulate to prevent the accumulation of heat in the same by the
compression of the air. By the action of this pump the air is continually and
simultaneously drawn from the parts A, B, C, of the circuits through the
perforations a, b, c, pipe U, air chamber V, and pipe W into the pump, as
indicated by the arrows, and is forced through the pipe W³, chamber V¹,
pipe U, and perforations a¹, b, c, into the parts A¹, B¹, C¹; of the
circuits, thus maintaining a continuous circulation of the air in each of
the circuits. The ends A, B, C, of the circuit tubes are fixed in an
air-tight manner against the faces of three tables or troughs Z, Z, Z³, in
which are the moveable receiving chambers H², H³, H³, of which there
are three connected together to each circuit, in order to provide means for
receiving the carriages arriving at short intervals without impeding the
dispatch of business.
The construction of such tables and receiving chambers which I prefer
to employ is shewn to an enlarged scale at Figures 4 and 5 on Sheet II.
of the Drawings, of which Figure 4 shews a transverse section through
one of the tables, and a longitudinal section through a receiving chamber,
and Figure 5 sbows a part longitudinal section through the table, and a
transverse section through one of the chambers. The chambers H¹ fit
in a more or less air-tight manner, with smooth sloping surfaces at one

page_text: end against the adjustable smooth sloping sides of the table Z¹ to which
the tube A is fixed, while the other ends of the chambers may either be
closed as shown at Figure 3, or they may be open as shown at Figure 4
and fit in a more or less air-tight manner against the other side of the table Z,
the weight of the chamber pressing against the sloping surface of the table,
tending to keep the surfaces in air-tight contact. An opening f is formed in
the side of the table, in continuation of the bore of the tube A, through which
the carriages or pistons pass from this tube into the chambers H'; these
chambers are formed by preference of thin sheet metal for the sake of lightness,
and are provided internally with brush surfaces d, as before mentioned, for
absorbing the momentum of the carriage as it enters, and a buffer spring e.
is fixed either'on the end of the chamber, when this is closed, or in the side
of the table Z, as shown at Figure 4, for finally stopping the carriage. As a
carriage enters one of the chambers H the set is slid to the one side or the
other of the circuit tubes so as to bring another empty one in front of the
tube for receiving the next carriage, while the chamber containing the carriage
just received is thereby brought in front of one of the apertures f¹ in the
sloping side of the table, through which the carriage is pushed out of the
chamber by means of a rod g, worked by a lever and introduced through a
hole in the other side of the table, as indicated at Figure 3. For dispatching
the carriages from the central station, each circuit is provided with double
dispatching chambers ¹, k, k³, 1, ³, k³, separated from each other and.
from their respective circuits by valves h¹³, h, i, i,, 7, so that when a
carriage is introduced, say, into'', the valve is opened so as to allow it to
pass into ; after which the valve h¹ is closed and h³ opened so as to
allow the carriage to enter the circuit tube; and to be propelled along the
same by the current of air entering through the perforations a¹, as 'before
described; the opening of the one -valve and the closing of the other may be
effected simultaneously by levers arranged in any well-known manner for
this purpose. The carriages employed for transmitting the dispatches or
parcels are by preference made cylindrical in form, and are so arranged that
they can be opened for the introduction of dispatches, letters, or parcels, and
they are provided in front and behind either with a pair of wheels at right
angles to each other, each wheel being nearly of the internal diameter of the
tube itself, or they are provided with cylindrical brushes fitting the tube.
The body of the piston or cylinder need not touch the internal surface of the
tube; because the friction produced by the wheels or brushes is so slight as
to render a close fit not necessary. :

page_text: At Figures 6 and 7 on Sheet .II. of the Drawings is shown the construction
of such carriages. At Figure 6 the carriage is composed of a light metallic
cylindle fixed at one end into a socket m, and provided at the other end
with a removeable cover n secured by a bayonet joint and spring catch, as
shown. The socket m and cover n have projecting rods o, p, upon which are
placed the cylindrical brushes q, r, fitting the interior of the circuit tube A.
The carriage at Figure 7 is of similar construction, but in place of the brushes
the socket m and cover n each carry by means of the framing o, p, two
wheels 8, s, t, t, at right angles to each other. and slightly less in diameter than
the diameter of the tube A. For introducing or removing the. letters or
dispatches the cover n is removed.
When the pneumatic circuit is of considerable extent and the..tube 'is
of small diameter the speed of transit of the pistons may be considerably
increased by the employment of hydrogen or light carburetted hydrogen.
gas in the tube in place of atmospheric air, which gas might be supplied
continually at the pumping station to make up for losses through leakage,
and to prevent such leakage the maximum pressure in the tube may be
made never to exceed that of the external atmosphere, which may also be,
preferable even when atmospheric air is used. In introducing fresh air or.
gases into the tube to make up for leakage such air or gases are by preferenco
first made to pass through a drying chamber containing dry lime or other
substances that will take up the moisture from the air or gas before it enters
the tube.
.
:
As a number of the pistons or cylindrical carriages may require to be
continually dispatched from the central station to the intermediate stations. on
the circuit information is conveyed to the particular station for which a
certain carriage is destined by means either of an electric telegraph signal
which is given at the central station at the time when the carriage is intro-
duced, and by causing the said signal to set in motion a clockwork mechanism.
at the said station a second signal may thereby be given after a lapse of time
corresponding with the time the carriage takes to travel from the central
station to the intermediate station in question, thereby warning the attendant
of the proper moment, when he has to. divert. the main pipe into the receiving
chamber; or the carriages may be dispatched at preconcerted intervals of
time to the respective stations, where electric clocks are made to indicate to
the attendant the exact time when they have to expect a carriage. The
carriage in approaching the station into which it is to .be .received may be
made to give warning of its approach to the attendant by striking against and.

page_text: depressing a lever fixed in the tube at a certain distance from the station and
made to project slightly into the tube, which lever in being depressed causes a
rod passing in an air-tight manner through the tube to establish a contact in a
galvanic circuit, the current passing through which is made to ring an alarum
at the station.
As before stated, a number of the before described pneumatic circuits
may be made to communicate with one central station, and in large towns
one or more of the intermediate stations on any circuit may be constituted a
branch central station, from which again a series of pneumatic circuits may
branch out.
At intermediate stations, where carriages come in at very frequent
intervals, two or more receiving chambers may be provided in a similar
manner as described with reference to the central station, into which successivo
carriages or pistons may be "switched" in rotation to allow time for their
removal.
It will be readily understood that in working pneumatic circuits on the
above described principle a great number of pistons may be travelling within
the tube at the same time, both coming to and going from the central and
intermediate stations, but all travelling in the same direction in the tubular
circuit, thus rendering this system capable of forwarding a great number of
dispatches or parcels at frequent intervals without its being for this purpose
necessary to attain a high rate of speed of transit.
'It will also be seen that by this system of causing the air to circulate through
a closed circuit no loss of power can be occasioned by any escape of the pro-
pelling medium past the carriages in consequence of these not fitting the tube
accurately, and the loss of power through the escape of the propelling medium
before described as taking place in pneumatic tubes having terminal stations
at every arrival of a carriage at the end station is by the before-described
system more or less entirely avoided, the only escape beyond leakage that can
take place being the small quantity of air or gas that passes into the receiving
chamber together with the carriage, and this is reduced to a minimum by
making the chambers only slightly longer than the carriages.
Having thus described the nature of this Invention, and in what manner
the same is to be performed, I wish it to be understood that I do not limit
myself to the precise arrangements for carrying the same into effect as herein-
before described with reference to the accompanying Drawings, as these may
be variously modified without departing from the nature of the Invention, nor
do I claim as novel all the various before-described details of construction when

page_text: taken. separate and apart from their combination for the purposes of this
Invention; but what I claim is,-
First, arranging pneumatic tubes for the conveyance of letters and other
light articles in such manner as to constitute closed circuits in which the air
or other gas serving to propel the carriages or pistons containing the letters or
other light articles is made to circulate continuously in one direction only by
means of a pump or pumps communicating at one or more points with the
circuit, such circuit having stations at different points at which the said carriages
or pistons are intercepted on their passage round the circuit, and where they
are introduced into the circuit to be forwarded to other stations, substantially
as herein-before described.
Second, arranging a portion of the pneumatic circuit tube at the stations so
as to be capable of being diverted from the circuit to one or more receiving
chambers into which the carriages or pistons to be intercepted pass, the
circulation of the air or gas in the circuit being at the same time maintained
by means of a "by-pass" communicating with the circuit at points in front of
and behind the moveable part, substantially as herein-before described with
reference to Figure 2 on Sheet I. of the accompanying Drawings.
Third, arranging a branch tube into which the carriages to be forwarded
are inserted so as to move in front of the opening in the circuit tube formed
by the diversion of the moveable part or switch, thereby causing the carriage
contained in such branch to enter into and be conveyed along the circuit,
substantially as described with reference to Figure 2 on Sheet I. of the
accompanying Drawings.
Fourth, constructing receiving chambers into which the carriages or
pistons are made to pass from the pneumatic circuit, and having brush
surfaces or equivalent appliances upon their sides for absorbing the
momentum of the carriages as they pass in, substantially as herein-before
described.
Fifth, arranging two or more closed pneumatic circuits in connection with
one central pumping station, substantially as herein-before described.
Sixth, employing hydrogen or light carburetted hydrogen gas as the pro-
pelling medium in the place of air in pneumatic circuits for the purposes
herein-before set forth.
Seventh, causing the air or gas serving as the propelling medium to pass in
contact with dry lime or other suitable bydroscopic substance in order to
absorb any moisture therefrom before entering the pneumatic circuit.
Eighth, I claim in combination the before-described system of and apparatus

page_text: for conveying letters, telegraphic dispatches, and other light articles through
closed pneumatic circuits.*
In witness whereof, I, the said Charles William Siemens, have hereunto
set my hand and seal, this Twenty-second day of November, in the
year of our Lord One thousand eight hundred and sixty-seven.
Witness,
THO". TAYLOR,
20, Southampton Bldgs., 1
Chancery Lane.
C. W. SIEMENS. (L.S.)