continued to characterize the development of the block system from
that early day to the present. The electrical application to which
reference is made in the preceding quotation was that of the needle,
which by its varying position could indicate either “line clear” or
“line blocked.” In 1851 electric bells were used in railroad signalling
on the Southeastern Railway of England. Various other developments were
completed from time to time in Great Britain until the Sykes system
of block signalling was patented in 1875. One of the main features of
the system, and perhaps the most prominent, was the control of the
track signals at the entrance end of the block by the signalman at the
advance end. He exerted this control by electrically operated locks.
About 1876 the Pennsylvania Railroad introduced the block system into
the United States, which has since been greatly developed in a number
of different forms, and its use has been widely extended over many if
not most of the great railroad systems of the country. It is not only
used for the movement of trains, but also for the protection of such
special danger-points as switches, cross-overs, junctions, drawbridges,
heavy descending grades, sharp curves, and other points needing the
protection which a well-designed block system affords.
=268. Code of American Railway Association.=—The code of the American
Railway Association gives the following definitions among others
pertaining to the block system:
_Block._—A length of track of defined limits, the use of which by
trains is controlled by block signals.
_Block Station._—The office from which block signals are operated.
_Block Signal._—A fixed signal controlling the use of a block.
_Home Block Signal._—A fixed signal at the entrance of a block to
control trains in entering and using said block.
_Distant Block Signal._—A fixed signal of distinctive character used in
connection with a home block signal to regulate the approach thereto.
_Advance Block Signal._—A fixed signal placed in advance of a home
block signal to provide a supplementary block between the home block
signal and the advance block signal.
_Block System._—A series of consecutive blocks controlled by block
signals.
_Telegraph Block System._—One in which the signals are operated
manually upon telegraphic information.
_Controlled-Manual Block System._—One in which the signals are operated
manually, and by its construction requires the co-operation of a
signalman at both ends of the block to display a clear signal.
_Automatic Block System._—One in which the signals are operated by
electric, pneumatic, or other agency, actuated by a train or by certain
conditions affecting the use of a block.
=268a. The Block.=—It is seen by these definitions that what may be
called the unit in railroad signalling is the “block”; it may be of
almost any length from a few hundred feet to 6 or 8 miles, or even
more. On a single-track railroad it may evidently extend from one side
track or passing-place to another. Over portions of lines carrying
heavy traffic it may be a half-mile or less. The length of block will
depend, then, upon the intensity and kind of traffic, the physical
features of the line, such as curvature, grade, sidings, cross-overs,
and other similar features, the location, whether in cities, towns, or
open country, as well as upon other elements affecting conditions of
operation which it is desirable to attain.
=269. Three Classes of Railroad Signals—The Disc.=—The signals used
in railroad operation may mainly be divided into three classes:
semaphores, banners, and discs. In general they may convey information
by form, position, and color. The disc is used by causing it to appear
and disappear before an aperture, usually a little larger than itself,
in a case standing perhaps 10 or 12 feet high alongside the track, and
is admirably typified in the Hall electric signal. On account of its
shape, the case in which the disc is operated is frequently called
the banjo, as it is quite similar in shape to that musical instrument
placed in a vertical position, the key end resting on the ground.
=270. The Banner Signal.=—The banner signal is usually operated by
rotation about a vertical axis, frequently in connection with switches.
Its full face painted red, exposed with its plane at right angles to
the track, indicates “danger” or “stop.” With its face turned parallel
to the track, showing only its edge to approaching trains, a “clear”
line or “safety” is indicated.
In the present development of railroad signalling the banner and disc
patterns have a comparatively limited application, although, on the
whole, they are largely used. The banner signal is mostly employed in
the manual operation of switches, turn-outs, and cross-overs, and for
other local purposes, particularly on lines of light traffic.
[Illustration: FIG. 10.—Semaphore Signals.]
=271. The Semaphore.=—The semaphore is now mainly used in connection
with block signalling. Like many other appliances in railroad
signalling it was first used in England, by Mr. C. H. Gregory, about
1841. Its name is derived from the combination of two Greek words
signifying a sign-bearer. It consists of a post varying in height
from about 3 to 35 or 40 feet, carrying an arm at its top from 3 to
5 feet long, pivoted within a foot or 18 inches of one end, the long
end suitably shaped and painted and the other arranged with a lens so
that when operated at night in connection with a lamp it may exhibit a
properly colored light. The post of the semaphore is placed alongside
the track so as to be on the right-hand side of an approaching train,
the long arm rising and falling as a signal away from the track and in
a plane at right angles to it. The other arm of the semaphore signal
may be connected by wires or rods and light chains running over pulleys
with suitable levers and weights operated either in a near-by signal
cabin or by a signalman stationed near the semaphore itself; or it may
be operated by electric or pneumatic power, as in many of the later
installations. The semaphore may, therefore, be operated at the post or
by suitable appliances at a distance.
[Illustration: Semaphore on Pennsylvania Railroad.]
=272. Colors for Signalling.=—The colors used either for painted
signals for daylight exposure or for coloring lenses for night
signalling are red, white, and green, as ordinarily employed in
this country; red signifying “danger” or “stop,” white signifying
“safety” or “clear track,” and green signifying “caution” or “proceed
with train under control,” indicating that a train may go forward
cautiously, expecting to find an obstruction or occupied track. In
England green is largely employed to indicate “safety” or “clear
track,” on the ground that a white light is so similar to any other in
its vicinity that the latter may too easily be mistaken for a signal.
While there is some diversity of views in this country on that point,
the consensus of engineering opinion seems to favor the retention of
the white for the track safety signal.
=273. Indications of the Semaphore.=—It is evident that a semaphore
affords facilities of form, position, and color in its use for the
purpose of signalling. The horizontal position is the most striking
for the semaphore arm, as it then extends at right angles to the post
and to the right or away from the track; this position is, therefore,
taken to indicate “danger” or “stop.” No train may, therefore, proceed
against a horizontal semaphore arm.
It might at first sight appear that the vertical position of the
semaphore arm close against the post could be taken to indicate
“safety” or “clear track” or “proceed,” but experience has shown that
such a position may be injudicious, except under special conditions
where it has lately been employed to make that indication. If the
semaphore arm should be knocked or blown from the ordinary post,
the engineman of an approaching train probably would not be able to
detect the actual condition of things and might accept the appearance
of the semaphore as indicating a clear line, thus justifying himself
in proceeding at full speed, while the signalman in his cabin might
have placed the signal at “danger.” A position of the semaphore arm,
therefore, at an angle of 65° or 70° below the horizontal is usually
taken as a safety signal. This position is in marked contrast to the
horizontal arm and at the same time makes the absence of the semaphore
arm impossible without immediate detection from an approaching
locomotive. After dark the semaphore in a position of danger exhibits
a red light through the lens in its short arm when the long arm is at
the “danger” position or horizontal. Similarly, when the long arm is in
the safety position a white light is exhibited through the lens in the
shorter arm, so that the respective conditions of clear or obstructed
track are made evident to the engineman as well by night as by day on
his approach to the semaphore.
In some of the latest signal work three positions of the semaphore
arm on one post, known as three-position block signalling, have been
employed. In this system a special post, frequently on a signal bridge
over the track, permits the vertical position of the semaphore arm
to indicate “clear track,” while the diagonal or inclined position
below the horizontal indicates “caution.” In the Mozier three-position
signal a diagonal or inclined position above the horizontal indicates
“caution” an addition to the two usual positions of “stop” and “clear.”
These are the elements, so to speak, of railroad signalling at the
present day. They are combined with various appliances and in various
sequences, so as to express all the varied conditions of the track
structure which affect the operation of the road or the movement of
trains upon it. These combinations and the appliances employed in them
are more or less involved in their principal features and complicated
in their details, although the main principles and salient points are
simple and may easily be exhibited as to their mode of operation and
general results. In this treatment of the subject it will only be
possible to accomplish these general purposes without attempting to set
forth the mechanical details by which the main purposes of railroad
signalling are accomplished.
=274. General Character of Block System.=—It is evident from what has
already been stated that the block system of signalling involves the
use of fixed signals located so as to convey promptly to approaching
trains certain information as to the condition of points of danger
approached. Furthermore, this system of signals is designed and
operated on the assumption that every point is to be considered as a
danger-point until information is given that a condition of safety
exists. The usual position of signals, or what may be called the normal
position, is that of “danger,” and no position of “safety” is to be
given to any signal except to permit a train to pass into a block whose
condition of safety or clear track is absolutely assured. These are
the ground principles on which the signal systems to be considered are
designed and operated, although there are some conditions under which
the normal signal position may be that of safety.
=275. Block Systems in Use.=—The block systems now in general use are:
The Manual, in which the signals at each end of each block are wholly
controlled and operated by the signalman at each signal point.
The Controlled-Manual, in which the signals at the entrance to each
block are controlled either electrically or in some other manner by
the signalman at the other extremity of that block, but are operated
subject to that control by the signalman at the entrance of the block.
The Auto-Manual, in which the signals are generally operated and
controlled as in the Manual or Controlled-Manual, except that they are
automatically returned to the danger position as the rear car of a
moving train passes them.
The Automatic, in which the operation of the signals is wholly
automatic and generally by electricity, or by a combination of electric
and pneumatic mechanism. In this system no signalmen are required.
The Machine, which is a controlled block system for single-track
operation and in which machines operated electrically with detachable
parts, as staffs, are employed in connection with other fixed signals
alongside the track.
The main features of these various systems of blocking are, in
respect to their signalling, the same, but the means for actuating or
manipulating the signals and the conditions under which moving trains
receive the necessary instructions are different. They all have the
same main objects in view of improving railroad operation by enhancing
both safety and facility of train movement.
“Absolute” blocking is that system of block signalling which absolutely
prevents one train passing into a block until the preceding train is
entirely out of it, or, in other words, until the block is absolutely
clear.
“Permissive” blocking is, strictly speaking, the violation of the true
block system of signalling, since under it a train may under certain
precautionary conditions enter a block before the preceding train has
passed out of it.
=276. Locations of Signals.=—In proceeding to locate signals along a
railroad line it is imperative to recognize the preceding purposes
as controlling motives. Signals must be seen readily and clearly in
order to be of the greatest service to the enginemen of approaching
trains, and their positions must be selected with that end in view.
Locations of switches, cross-overs, junctions, and other similar track
features will control the locations of the signals which are to protect
them. The main or home signal in these special cases may usually be
placed from 50 to 200 feet from the point which is to be governed, the
so-called “distant” signal being placed about 2000 feet for level track
back of the main or home signal.
=277. Home, Distant, and Advance Signals.=—A complete system of signals
employed in blocking includes first of all the so-called “home” signal
at each extremity of a block, then at a distance of 2000 to 2500 feet
back from the home signal is placed the “distant” signal. The latter
is thus approached and passed before reaching the home signal. On the
other side of the “home” signal at least a maximum train length into
a block about to be entered by a moving train is placed the “advance”
signal. The distance of the advance signal from the home signal may
be 1500 to 2500 feet. As a moving train approaches the end of a
block it first meets the distant signal, the purpose of which is to
indicate what the engineman may expect to find at the home signal. If
the distant signal is in the danger position, he will pass it with
caution and place his train under control so as to be able to stop at
the home signal. If he finds the distant signal in a safety position,
indicating the same position of the home signal, he may approach the
latter without reducing speed, confident that the next section is clear
and ready for him. The advance signal forms a kind of secondary or
supplementary block into which the train, under certain conditions,
may enter when the block in which it is found is obstructed, but no
train may pass the advance signal unless the entire block is clear
except when, under permissive working, the train proceeds with caution,
expecting to find the track either obstructed or occupied. This group
of three signals—the distant, the home, and the advance—taken in
the order in which the moving train finds them, is located at each
extremity of the block. Although the home signal is said to control the
movement of trains in a block at the entrance to which it is found, as
a matter of fact it appears that the advance signal in the final event
holds that control.
=278. Typical Working of Auto-Controlled Manual System.=—The mode of
employing these signals can be illustrated in a typical way by the
diagrams, Figs, 11, 12, and 13, which exhibit in a skeleton manner
Pattenall’s improved Sykes system which belongs to the Auto-Controlled
Manual class. In these figures the end of block 1, the whole of blocks
2 and 3, and the beginning of block 4 are shown. Stations _A_, _B_,
and _C_ indicate the extremities of blocks. The signals _S_, _Sʹ_,
and _S″_ are the home signals, while _D_, _Dʹ_, and _D″_ indicate
distant signals, and _A_, _Aʹ_, and _A″_ advance signals. As the
diagrams indicate, the stretch of double-track road is represented
with east- and west-bound tracks. In order to simplify the diagrams,
signals and stations are shown for one track only; they would simply
be duplicated for the other track. The signal cabin is supposed to be
located at each station, and at that cabin are found the levers and
other appliances for working the signals operated there, the signals
themselves being exposed alongside the track. In each signal cabin
there is an indicator, as shown at _I_, _Iʹ_, and _I″_. On the face
of each indicator there are two slots, shown opposite the lines _E_
and _F_. In the upper of these slots appears either the word “Clear”
or “Blocked.” In the lower slot appears either the word “Passed” or
“On.” The significance of these words will appear presently. On this
indicator face at _P_, _Pʹ_, and _P″_ are located electric push-buttons
called plungers. The operation of the levers indicated at _L_, the
counterweights _d_, and the locking detail _l_ are evident from an
inspection of the figure, and need no special explanation. It is only
necessary to state that the locking-device _l_ holds the bar _bc_ until
it is released at the proper time, and that the counterweight may then
return the lever from its extreme leftward position to that at the
extreme right, at the same time placing the semaphore arm _S_ in the
position of danger. It is particularly important to bear in mind this
last observation. The counterweight is the feature of the system which
always holds the semaphore arm in the position of danger, making that
its normal position, except when it is put to safety for the passing of
a train.
[Illustration: FIG. 11.]
[Illustration: FIG. 12.]
[Illustration: FIG. 13.]
If a westward train is represented in Fig. 11 at _T_ as approaching
station _A_ to enter the block 2, both the distant signal _D_ and
the home signal _S_ being at danger, the system is so arranged that
the signalman at station _A_ cannot change those signals, i.e., to a
position of safety, until the signalman at station _B_ permits him to
do so. If the signalman at station _A_ desires to open block 2 for
the entrance of the train _T_, he asks the signalman at station _B_
by wire to release the lock _l_ to enable him to do so. If there is
no train in block 2, the signalman at station _B_ pushes the button
_P′_ or “plunges” it. This raises the lock _l_ at station _A_ and the
signalman immediately pulls the lever _L_ to its extreme leftward
position, throwing both the signals _S_ and _D_ to the position of
safety or clear, indicated by the dotted lines at _S_². At the same
time the indicator _E_ at station _A_ shows the words “Clear to _B_,”
while the slot _Fʹ_ at _B_ shows the words “On from _A_.” The signals
at stations _B_ and _C_ are supposed to be in their normal position of
danger, and the indicator _E′_ at station _B_ shows the words “Blocked
to _C_.” The home and distant signals _Sʹ_ and _Dʹ_ are now at danger,
but the train _T_ may enter block 2 and proceeds to do so, it being
remembered that the signalman at station _A_ cannot move the lever _L_,
as it has passed out of his control; not even the signalman at station
_B_ can give him power to do so. The train _T_ now passes station _A_
into block 2. As the last car passes over the point _G_ its wheels
strike what is called a track-treadle, an appliance having electrical
connection with the lock _l_. The effect of the wheels of the last car
of the train passing over the treadle at _G_ is to release lock _l_,
enabling the signalman at station _A_ immediately to raise the arms _S_
and _D_ to the position of danger. It is to be observed that he cannot
do this until the entire train has passed into block 2; nor, since his
plunger is locked by the same treadle at _G_, can he signal “Safety” or
“Clear” to the entrance of block 1. Hence no train can enter block 1 to
collide with the rear end of the train just entering block 2. When the
signalman at station _A_ has raised his signal _S_ to danger, it again
passes out of his control, indeed out of both his control and that of
the signalman at _B_, until the last car of the train passes over the
treadle _Gʹ_ at the entrance of block 3.
The train has now passed into block 2 and is approaching station _B_.
The signalman at _B_ asks _C_ by wire to release the lever _Lʹ_, and if
block 3 is clear, _C_ plunges at _P″_.
_C_ then throws his lever _Lʹ_ so as to place the home and distant
signals _Sʹ_ and _Dʹ_ at safety. The condition of things will then be
shown by Fig. 12. As soon as the last car of the train has passed over
the treadle at _Gʹ_ his lever _Lʹ_ will be released and he can then
throw the lever to the danger position, raising the home and distant
signals _Sʹ_ and _Dʹ_ to the horizontal. After the danger position is
assumed by the home signal _Sʹ_, as well as the distant signal _Dʹ_, he
has no power over them until the signalman at station _C_ confers it on
him by plunging the button _P″_.
While the train has been in block 2, the indicator _Iʹ_ has shown
“Blocked to _C_” and “Train on from _A_,” but as the train passes _B_
the indicator reads “Blocked to _C_” and “Train passed from _A_,”
while the indicator _I″_ at _C_ reads “Blocked to _D_” and “Train on
from _B_.” This condition of the signals and trains is shown by Fig.
13. Also, when the last car passes over the treadle _Gʹ_, but not till
then, _B_ may permit _A_ to admit a train to enter block 2 should _A_
so desire. Finally, when the train approaches _C_, the signalman at
that point asks _D_ to enable him to permit the train to enter block 4,
and _C_ confers the power by plunging if that block is clear. Fig. 13
exhibits the corresponding signals at _C_.
This sequence of operations is typical of what takes place in this
particular block signal system at the limits of every successive block,
and differs only in details characteristic of this system from those
which are performed in any other block signal system.
=279. General Results.=—It is seen first that no signalman can operate
a signal until the condition in the block ahead of him is such as to
make it proper for him to do so, and then he can only indicate what
is necessary for the safe entrance of the train into that block.
Furthermore, immediately on the passage of the train past his home
signal he must put the latter to danger or the counterweight may do it
for him, the train itself when in a safe position having conferred the
requisite power upon him. The signalman at the advance end of the block
always knows when the train is about to enter it, for he is obliged
to give his permission for that entrance. His indicator shows this
result, and will continue to show it until the train passes out of the
block. It is to be observed that the upper openings marked _E_ on the
indicator give information of the condition of the block in advance,
while the lower openings give information of the block in the rear.
It is particularly important to notice that after the signalman at the
advance end of a block has “plunged” his plunger remains locked and it
cannot be released until the train admitted to the block covered by
the plunger has completely passed out of that block, permitting the
track-treadle at the entrance to the next block to unlock the plunger.
This feature makes it impossible for one train to enter a block until
the preceding train has passed out of it.
If the permissive system of using a block be employed, in which the
train is permitted to enter that block before a preceding train leaves
it, the treadle gives no protection against a rear-end collision with
the first train. In such an exigency other devices must be used or the
following train must proceed cautiously, expecting to find the track
occupied.
=280. Distant Signals.=—Thus far the distant signals have been
treated incidentally only. They may be operated concurrently with
or independently of the home signal in such a way that if danger is
indicated, the distant signal gives its indication prior to that of the
home signal. In this manner protection is given to the rear of a train
approaching a block against the home signal set at “danger.” After the
obstruction is removed and the block cleared, the home signal is set at
“safety” before the distant signal is cleared.
=281. Function of Advance Signals.=—The advance signals are used when
for any purpose it is desired to form a short block in a regular block.
If, for instance, block 3 in Fig. 11 were obstructed by a train stopped
by some failure of a locomotive detail, a train approaching station _B_
in section 2 against the home signal _Sʹ_ set at “danger” would be
obliged to stop before entering block 3. It might then be permitted to
enter the latter block, to be stopped by the advance signal _Aʹ_ set at
“danger” or under instructions to pass it cautiously, expecting to find
the track obstructed. It is thus seen that the advance signal creates
what may be called an emergency block, and in reality finally controls
the movement of trains in the block in which it is located. It would
never be cleared unless the home signal were first cleared, nor would
it be set at “danger” unless the home signal gave the same indication.
The preceding operation of the block system of signalling controls the
movement of trains along a double-track line.
[Illustration: FIG. 14.]
=282. Signalling at a Single-track Crossing.=—A somewhat similar
sequence of signal operations controls train movements at a crossing,
whether single- or double-track. Fig. 14 illustrates the use of
signals required for the safe movement of trains at a single-track
railroad crossing, which is supposed to be that of a north-and-south
line crossing obliquely an east-and-west line. Precisely the same
arrangement of signals operated in the same manner would be required
if the crossing were at the angle of 90°. The signal cabin is placed,
as shown, as near as practicable to the actual intersection of tracks.
Trains may pass in either direction on either track, but in every
case they would be governed by the signals at the right-hand side of
the track as seen by the engineman. There will therefore be a set of
signals on both sides of each track, each set governing the movement
of trains in its own direction. Each home signal may be placed about
350 feet from the actual intersection, and each distant signal 1200
to 1500 feet from the home signal, or 1550 feet to 1800 feet from the
intersection. Each advance signal must be at least as far in advance
of the home signal as the maximum length of train, since it may be
used to stop a train, the rear car of which should completely pass the
home signal. In their normal positions every home signal should be set
at “danger,” carrying with them the distant signals giving the same
indication. The advance signals must also indicate “danger” with the
home signal. No train can then pass the crossing until the home and
distant signals indicate a clear line for it, the other signals at the
crossing, except possibly the advance signal, being set at “danger.”
If for any reason it is desired to hold the train after it is entirely
free of the crossing, the advance signal would also indicate “danger.”
It is thus seen that if the signals are properly set and obeyed, it is
impossible for two trains to attempt a crossing at the same time. It is
not an uncommon occurrence, however, for an engineman to run his train
against the danger signal, and in order to make it impossible for the
train to reach the crossing even under these circumstances a derailing
device is used. This derailing arrangement is shown in Fig. 14, about
300 feet from the crossing, although it may be placed from 300 to 500
feet from that point. Its purpose is to derail any train attempting
to make the crossing against the danger signal. The operation of the
derail is evident from the skeleton lines of the figure. When the home
signal is at danger the movable part of the derailing device is at this
point turned so as to catch the flanges of the wheels as they attempt
to pass it. The train is thus thrown upon the cross-ties at such a
distance from the crossing as will produce a stop before reaching it.
When the home signal is at safety the derail operated with the signal
is closed and the line is continuous. This combination of signals and
derail coacting serves efficiently to prevent collisions at crossings,
although trains may be occasionally derailed in accomplishing that end.
The preceding explanations of the use of signals and derail apply to
a train that may approach the crossing in either direction on either
track, as is obvious from an inspection of the diagram itself.
=283. Signalling at a Double-track Crossing.=—In the case of a
double-track crossing, the arrangement of signals and derails is
precisely the same as for a single-track crossing, each set of signals
shown in Fig. 15 covering one track. In other words, the line of single
track is to take the place of each rail with its set of signals in
that figure. There will be but four derails, one for each track only
on the approach to the crossing. The working of the signals with the
derails is precisely the same as has already been explained for the
single-track crossing.
[Illustration: FIG. 15.]
[Illustration: FIG. 16.]
=284. Signalling for Double-track Junction and Cross-over.=—Fig. 16
represents a skeleton diagram of signals required for a junction of
two double-track roads and a cross-over. This arrangement covers the
use of switches. The location of signals and signal cabin as shown is
self-explanatory, after what has already been stated in connection with
single- and double-track crossings. It will be observed that the home
signals for both the west-bound main and branch tracks are identical
in location, and are shown by the solid double flag, the distant
signal being shown by its notched end at a considerable distance back
of the double home signal. It will, furthermore, be observed that
at each home signal there is a derailing-switch interlocked, in the
lock-and-block system presently to be explained, with the home signals
operated simultaneously with them. If, therefore, an engineman attempts
to run his train past a home signal set at danger, the result will be
the derailment of his train, thus brought to rest before it can make
any collision with another. It is obvious in this case that if the
switches from the main to the branch tracks or at the extremities of
the cross-over are worked independently, they must be operated directly
in connection with the signals. For complete protection they should be
interlocked with the signals so that it would be impossible to clear
any signal without simultaneously setting the switches consistently
with those signals. The diagram exhibits clearly the indications which
must be made in order to effect any desired train movement at such a
junction of tracks.
=285. General Observations.=—Similar arrangements of signals, derails,
or switches must be made wherever switches, cross-overs, and junctions
are found, the detailed variations of those signals and switches being
made to meet the individual requirements of each local case. The
combinations of switches and switch-signals frequently become very
complicated in yards where the tracks are numerous and the combinations
exceedingly varied, in order to meet the conditions created by the
movement of trains into and out of the yard.
The preceding explanations are intended only to give a clear idea
of the main features of signalling, in order to secure the highest
degree of safety and facility in the movement of trains over a modern
railroad. While they exhibit the external or apparent combinations of
signals for that purpose, they do not touch in detail and scarcely
in general upon the mechanical appliances found in the signal cabin
and along the tracks required to accomplish the necessary signal
movements. The considerations in detail of those appliances would cover
extended examinations of purely mechanical, electrical, pneumatic, and
electro-pneumatic combinations too involved to be set forth in any but
the most extended and careful study. They have at the present time been
brought to a wonderful degree of mechanical perfection and afford a
field of most interesting and profitable study, into which, however, it
is not possible in these general statements of the subject to enter.
[Illustration: FIG. 17.]
=286. Interlocking-machines.=—The earliest machine perfected for
use in this department of railroad signalling was the Saxby and
Farmer interlocking-machine, first brought out in England and
subsequently introduced in this country between 1874 and 1876. This
machine has been much improved since and has been widely used. Other
interlocking-machines have also been devised and used in this country
in connection with the most improved systems of signalling, until
at the present time a high degree of mechanical excellence has been
reached.
The interlocking-machine in what is called the lock-and-block system of
signalling is designed to operate signals, or signals in connection
with switches, derailing-points, or other dangerous track features, so
as to make it impossible for a signalman to make a wrong combination,
that is, a combination in which the signals will induce the engineman
to run his train into danger. The signals and switches or other track
details are so connected and interlocked with each other as to form
certain desired combinations by the movement of designated levers in
the signal cabin or tower. These combinations are predetermined in
the design and connections of the appliances used, and they cannot
be changed when once made except by design or by breakage of the
parts; they cannot be deranged by any action of the signalman. He
may delay trains by awkward or even wrong movement of levers, but he
cannot actually clear his signals for the movement of a train without
simultaneously giving that train a clear and safe track. As has been
stated, he cannot organize an accident. Figs. 17 and 18 show banks or
series of levers belonging to interlocking-machines. As is evident
from these figures, the levers are numerous if the machine operates
the switches and signals of a large yard, for the simple reason
that a great many combinations must be made in order to meet the
requirements of train movements in such a yard. The signalman, however,
makes himself acquainted with the various combinations requisite for
outgoing and incoming trains and the possible movements required
for the shifting or hauling out of empty trains. He has before him
diagrams showing in full the lever movements which must be made for
the accomplishment of any or of all these movements, and he simply
follows the directions of the diagrams and his instructions in the
performance of his duty. He cannot derange the combinations, although
he may be slow in reaching them. The locking-frame which compels him
to make a clear track whenever his signals give a clear indication
to the engineman lies below the lower end of the levers seen in the
figures. The short arms of the levers carry tappets with notches
in their edges into which fit pointed pieces of metal or dogs; the
arrangement of these notches and dogs is such as to make the desired
combinations and no others. It will be observed that a spring-latch
handle projects from a point near the upper end of each lever where
the latter is grasped in operating the machine. This spring-latch
handle must be pressed close to the lever before the latter can be
moved. The pressing of the spring-latch handle against the lever
effects a suitable train of unlocking before which the lever cannot
be moved and after which it is thrown over to the full limit and
locked there. The desired combination for the movement of the train
through any number of switches may require a similar movement of a
number of levers, but the entire movement of that set, as required,
must be completely effected before the signals are cleared, and when
they are so cleared the right combination forming a clear track for
the train, and that one only, is secured. These meagre and superficial
statements indicate in a general way, however imperfectly, the ends
attained in a modern interlocking-machine. They secure for railroad
traffic as nearly as possible an absolutely safe track. They eliminate,
as far as it is possible to do so, the inefficiency of human nature,
the erratic, indifferent, or wilfully negligent features of human
agency, and substitute therefor the certainty of efficient mechanical
appliances. In some and perhaps many States grade crossings are
required by statute to adopt measures that are equivalent to the most
advanced lock-and-block system of signalling. So vast has become
railroad traffic upon the great trunk lines of the country that it
would be impossible to operate them at all without the perfected modern
systems of railroad signalling. They constitute the means by which all
train movements are controlled, and without such systems great modern
railroads could not be operated.
[Illustration: FIG. 18.]
The swiftly moving “limited” express passenger trains, equipped with
practically every luxury of modern life, speed their way so swiftly
and smoothly over many hundreds of miles without the incident of an
interruption, and in such a regular and matter-of-fact way, that the
suggestion of an intricate system of signalling governing its movements
is never thought of. Yet such a train moves not a yard over its track
without the saving authority of its block signals. If the engineman
were to neglect even for a mile the indication of the semaphore, he
would place in fatal peril the safety of his train and of every life in
it.
=287. Methods of Applying Power in Systems of Signalling.=—The
mechanical appliances used in accomplishing these ends are among the
most efficient in character and delicate yet certain in motive power
which engineering science has yet produced. The electric circuit formed
by the rails of the track plays a most important part, particularly in
securing the safety of the rear of the train in making it absolutely
certain whether even rear cars that may have broken away have either
passed out of the block or are still in it. The electric circuit in one
application or another was among the earliest means used in railroad
signalling. Electric power is also used in connection with compressed
air for the working of signals. Among the latest and perhaps the most
advanced types of lock-and-block signalling is that which is actuated
by low-pressure compressed air, the maximum pressure being 15 pounds
only per square inch. The compressed air is supplied by a simple
compressor, and it is communicated from the signal cabin to the most
remote signal or switch by pipes and suitable cylinders fitted with
pistons controlled by valves, thus effecting the final signal or switch
movements. It has been successfully applied at the yard of the Grand
Central Station in New York City and at many other similar points. In
this connection it is interesting to observe that while the original
Saxby and Farmer interlocking-machine was installed from England in
this country, as has already been observed, about 1875, American
engineers have within a year reciprocated the favor by furnishing and
putting in place most successfully in one of the great railroad yards
of London the first low-pressure pneumatic lock-and-block system[8]
found in Great Britain.
[8] By Standard Railroad Signal Company of Troy, N. Y.
=288. Train-staff Signalling.=—The lock-and-block system gives
the highest degree of security attainable at the present time for
double-track railroad traffic, but the simpler character of the
single-track railroad business can be advantageously controlled by a
somewhat simpler and less expensive system, which is a modification
of the old train-staff method. It is one of the “machine” methods of
signalling. The type which has been used widely in England, Australia
and India, and to some extent in this country is called the Webb and
Thompson train-staff machine, shown in Fig. 19. It will be observed
that the machine contains ten staffs (18 to 20 inches long and 1 to 1¼
inches in diameter), but as many as fifteen are sometimes used. These
staffs can be removed from the machine at one end of a section of the
road at which a train is to enter, only by permission from the operator
at the farther end of the section. If the station at the entrance to
that section is called _A_, and the station at the farther end _X_, the
following description of the operation of the instrument is given by
Mr. Charles Hansel in a very concise and excellent manner:
[Illustration: FIG. 19.—Webb and Thompson Train-staff Machine.]
“When a train is ready to move from _A_ to _X_ the operator at _A_
presses down the lever which is seen at the bottom of the right-hand
dial, sounding one bell at _X_, which is for the purpose of calling
the attention of the operator at _X_ to the fact that _A_ desires to
send a train forward. The operator at _X_ acknowledges the call by
pressing the lever on his instrument, sounding a bell in the tower at
_A_. The operator at _A_ then asks permission from _X_ to withdraw
staff by pressing down the lever before mentioned three times, giving
three rings on the bell at _X_, and immediately turns his right-hand
pointer to the left, leaving it in the horizontal position pointing to
the words ‘For staff,’ indicating that he desires operator at _X_ to
release his instrument so that he can take a staff or train order from
it. If there is no train or any portion of a train between _A_ and _X_,
the holding down of the lever at _X_ closes the circuit in the lock
magnets at _A_, which enables the operator at _A_ to withdraw a staff.
As soon as this staff is removed from _A_, _A_ turns the left-hand
pointer to the words ‘Staff out,’ and in removing this staff from the
instrument _A_ the galvanometer needle which is seen in the centre
of the instrument between the two dials vibrates, indicating to the
operator at _X_ that _A_ has withdrawn his staff. _X_ then releases
the lever which he has held down in order that _A_ might withdraw a
staff and turns his left-hand indicator to ‘Staff out,’ and with this
position of the instrument a staff cannot be withdrawn from either one.
“The first method of delivering this staff to the engineer as a train
order was to place it in a staff-crane, which crane was located on the
platform outside of the block station. With the staff in this position
it has been found in actual practice that the engineman can pick it up
while his train is running at a speed of 30 miles per hour. A second
staff cannot be removed from _A_ nor a staff removed from _X_ until
this staff which was taken by the engineman in going from _A_ to _X_
is placed in the staff instrument at _X_; consequently the delivering
of a staff from _A_ to the engineman gives him absolute control of the
section between _A_ and _X_.
“This train order staff also controls all switches leading from the
main line between _A_ and _X_, for with the style of switch-stand which
we have designed for the purpose the trainman cannot open the switch
until he has secured the staff from the engineman and inserted it in
the switch-stand, and as soon as he throws the switch-lever and opens
the switch he fastens the train-staff in the switch-stand, and it
cannot be removed until the switchman has closed and locked the switch
for the main line. When this is done he may remove the train-staff and
return it to the engineman. It will thus be seen that this train order,
in the shape of a staff, gives the engineman absolute control over the
section, and also insures that all switches from the main line are set
properly before he can deliver the train-staff to the instrument at _X_.
“In order that the operator at _X_ may be assured that the entire train
has passed his station, we may divide the staff in two and deliver one
half to the engineman and the other half to the trainman on the caboose
or rear end of the train, and it will be necessary for the operator at
_X_ to have the two halves so that he may complete the staff in order
to insert it into the staff instrument at _X_, as it is impossible to
insert a portion of the staff; it must be entirely complete before it
can be returned to the staff instrument.”
Instead of using the entire staff as a whole or in two parts, Mr.
Hansel suggests that one or more rings on the body of the staff be
removed from the latter and given to the engineman or other trainman to
be placed upon a corresponding staff at the extreme end of the section.
This would answer the purpose, for no staff can be inserted in a
machine unless all the rings are in their proper positions. These rings
can be taken up by a train moving at any speed from a suitable crane at
any point alongside the track.
For a rapid movement of trains on a single-track railroad under this
staff system an engineman must know before he approaches the end of the
section whether the staff is ready for delivery to him. In order to
accomplish that purpose the usual distant and home signals may readily
be employed. The distant signal would show him what to expect, so that
he would approach the entrance to the section either at full speed or
with his train under control according to the indication. Similarly,
electric circuits may be employed in connection with the staff or rings
in the control of signals which it may be desired to employ.
The electric train-staff may also be used in a permissive block system,
the section of the track between stations _A_ and _X_ constituting
the block. In Fig. 19, showing the machine, a horizontal arm is seen
to extend across its face and to the right. This is the permissive
attachment which must be operated by the special staff shown on the
left half of the machine about midway of its height. If it is desired
to run two or three trains or two or three sections of the same train
from _A_ before admitting a train at _X_ in the opposite direction,
the operator at _A_ so advises the operator at _X_. The latter then
permits _A_ to remove the special staff with which the extreme
right-hand end of the permissive attachment is unlocked and a tablet
taken out. This tablet is equivalent to a train order and is given
to the train immediately starting from _A_. A second tablet is given
in a similar manner to the second section or train, and a third to
the third section. The last section of train or train itself starting
from _A_ takes all the remaining tablets and the special staff for
insertion in the machine at _X_. In this manner head-to-head collisions
are prevented when a number of trains are passing through the block
in the same direction before the entrance of a train in the opposite
direction. This system has been found to work satisfactorily where
it has been used in this country, although its use has been quite
limited. Evidently, in itself, it is not sufficient to prevent rear-end
collisions in a block between trains moving in the same direction. In
order to avoid such collisions where a train falls behind its schedule
time or for any reason is stopped in a block, prompt use must be made
of rear flagmen or other means to stop or to control the movement of
the first following train.
[Illustration: FIG. 20.]
The most improved form of high-speed train-staff machine is shown in
Fig. 20, as made and installed by the Union Switch and Signal Company
and used by a number of the largest railroad systems of the United
States. In these machines the staffs are but a few ounces in weight.
CHAPTER XXIII.
=289. Evolution of the Locomotive.=—The evolution of the steam
locomotive may be called the most spectacular portion of the
development of railroad engineering. The enormous engines used at
the present time for hauling both heavy freight and fast passenger
trains possess little in common, in respect of their principal
features, with the crude machines, awkward in appearance and of little
hauling capacity, which were used in the early part of the nineteenth
century in the beginning of railroad operation. The primitive and
ill-proportioned machine, ungainly in the highest degree, designed and
built by Trevithick as far back as 1803, was a true progenitor of the
modern locomotive, although the family resemblance is not at first very
evident. Several such locomotive machines were designed and operated
between 1800 and 1829 when Stevenson’s Rocket was brought out. The
water was carried in a boiler on a wagon immediately behind the engine,
and the steam-cylinder in those early machines was placed almost
anywhere but where it now seems to belong. The Rocket has some general
features of resemblance to the machines built seventy years later, but
when placed side by side it might easily be supposed that seven hundred
years rather than seventy had elapsed between the two productions of
the shop.
After the famous locomotive trial in which Robert Stevenson distanced
his competitors, the design of the locomotive advanced rapidly, and
it was but a few years later when the modern locomotive began to be
accurately foreshadowed in the machines then constructed. This was true
both in England and the United States.
The first steam locomotive in this country is believed to be the
machine built by John Stevens at Hoboken, N. J., in 1825 and operated
in 1825-27. This locomotive has practically the arrangement of boiler
and cylinder which is found upon the modern contractors’ engines used
for pile-driving, hoisting, and similar operations. It would certainly
be difficult to imagine that it had any relation to the great express
and freight locomotives of the present day. The rectilinear motions
of the piston were transformed into the rotary motion of the wheels
by means of gearing consisting of a simple arrangement of cog-wheels.
About the same time a model of an English locomotive called the
Stockton and Darlington No. 1 was brought to the United States by Mr.
William Strickland of Philadelphia. The next important step in American
locomotive development was the construction of the locomotive “John
Bull” for the Camden and Amboy Railroad Company in the English shops
of Stevenson & Company in the years 1830-31. This machine has the
general features, although not the large dimensions, of many modern
locomotives. The cow-catcher is a little more elaborate in design and
far-reaching in its proportions than the similar appendage of the
present day, but the general arrangement of the fire-box and boiler,
the steam-cylinders, the driving-wheels and smoke-stack is quite
similar to a modern American locomotive. This machine, “John Bull,” and
train made the trip from New York City to Chicago and return under its
own steam in 1893. It was one of the prominent features of the World’s
Columbian Exposition. It rests in the National Museum at Washington,
where it is one of the most interesting early remains of mechanical
engineering in this country. One of the cars used in this train was
the original used on the Camden and Amboy Road about 1836. Its body
was used as a chicken-coop at South Amboy, N. J., for many years, and
was rescued from this condition of degradation for the purpose of the
Exposition trip in 1893. The original driving-wheels had locust spokes
and felloes, the hubs and tires being of iron.
The locomotive “George Washington” was built, as a considerable
number have been since, with one driving-axle, and was designed to
be used on heavy grades. This machine was built by William Norris &
Sons of Philadelphia, who were the progenitors of the present great
establishment of the Baldwin Locomotive Works. While the development
of the locomotive was subjected to many vicissitudes in principles,
general arrangement, and size in order to meet the varying requirements
of different roads as well as the fancies or more rational ideas of the
designers, its advance was rapid. As early as 1846 we find practically
the modern consolidation type, followed in 1851 by the ordinary
eight-wheel engine of which thousands have been constructed within
the past fifty years. The first Mogul built by the Baldwin Locomotive
Works was almost if not quite as early in the field. Both these types
of machines carry the principal portion of their weight upon the
driving-wheels and were calculated to yield a high tractive capacity,
especially as the weights of the engines increased. The weight of the
little “John Bull” was but 22,425 pounds, while that of the great
modern machine may be as much as 267,800 pounds, with 53,500 pounds on
a single driving-axle.
=290. Increase of Locomotive Weight and Rate of Combustion of
Fuel.=—The development of railroad business in the United States has
been so rapid as to create rigorous exactions of every feature of a
locomotive calculated to increase its tractive force. Any enhancement
of train-load without increasing the costs of the train force or other
cost of movement will obviously lead to economy in transportation.
In order that the locomotive may yield the correspondingly augmented
tractive force the weight resting upon the drivers must be increased,
which means a greater machine and at the same time higher working
pressures of steam. This demands greater boiler capacity and strength
and a proportionately increased rate of combustion, so as to move the
locomotive and train by the stored-up energy of the fuel transformed in
the engine through steam pressure. The higher that pressure the greater
the amount of energy stored up in a unit of weight of the steam and the
greater will be the capacity of a given amount of water to perform the
work of hauling a train. The greater the weight of train moved and the
greater its speed the more energy must be supplied by the steam, and,
again, that can only be done with a correspondingly greater consumption
of fuel. In the early days of the small and crude machines to which
allusion has already been made the simplest fuel was sufficiently
effective. As the duties performed by the locomotive became more
intense a higher grade of fuel, i.e., one in which a greater amount of
heat energy is stored per unit of weight, was required. Both anthracite
and bituminous coal have admirably filled these requirements. The
movement of a great modern locomotive and its train at an average
rate of 30 to 60 miles per hour requires the combustion of fuel at a
high rate and the rapid evaporation of steam at pressures of 180 to
225 or more pounds per square inch. The consumption of coal by such a
locomotive may reach 100 pounds per minute, and two barrels of water
may be evaporated in the same time. This latter rate would require over
a gallon of water per second to be ejected through the stack as exhaust
steam. Some of the most marked improvements in locomotive practice have
been made practically within the past six or seven years in order to
meet these exacting requirements.
While the operations of locomotives will obviously depend largely upon
quality of fuel, speed, and other conditions, the investigations of
Prof. W. F. M. Goss and others appear to indicate that 12 to 14 pounds
of water per hour may be evaporated by a good locomotive boiler per
square foot of heating surface, and that 25 to 30 pounds of steam will
be required per indicated horse-power per hour.
=291. Principal Parts of a Modern Locomotive.=—The principal features
of a modern locomotive are the boiler with the smoke-stack placed on
the front end and the fire-box or furnace at the rear, the tubes, about
2 inches in diameter, through which the hot gases of combustion pass
from the furnace to the smoke-stack, the steam-cylinders with their
fittings of valves and valve movements, and the driving-wheels. These
features must all be designed more or less in reference to each other,
and whatever improvements have been made are indicated almost entirely
by the relative or absolute dimensions of those main features. The
boiler must be of sufficient size so that the water contained in it
may afford a free steam production, requiring in turn a corresponding
furnace capacity with the resulting heating surface. The latter is
that aggregate surface of the interior chambers of the boiler through
which the heat produced by combustion finds its way to the water
evaporated in steam; it is composed almost entirely of the surfaces
of the steel plates of the fire-box and of the numerous tubes running
through the boiler and parallel to its centre, exposed to the hot gases
of combustion and in contact with the water on the opposite sides of
those plates. Evidently an increase in size of the fire-box with the
correspondingly increased combustion will furnish a proportionally
larger amount of steam at the desired high pressure, but an increase
in the size of the fire-box is limited both in length and in width. It
is found that it is essentially impracticable for a fireman to serve a
fire-box more than about 10 feet in length. The maximum width of the
locomotive limits the width of the fire-box.
[Illustration: FIG. 21.]
=292. The Wootten Fire-box and Boiler.=—As the demand arose for an
enlarged furnace the width of the latter was restricted by the width
between the driving-wheel tires, less than 4 feet 6 inches. That
difficulty was overcome by what is known as the Wootten fire-box, which
was brought out by John E. Wootten of the Philadelphia and Reading
Railroad about 1877, and has since been developed and greatly improved
by others. The Wootten boiler with its sloping top and great width
extending out over the rear driving-wheels presented a rather curious
appearance and was a distinct departure in locomotive boiler design.
Fig. 21 shows an elevation and two sections of the original Wootten
type of boiler. It will be noticed that in front of the fire-box there
is a combustion-chamber of considerable length, 2½ to 3 feet long. This
boiler was first designed to burn the poorer grades of fuel, such as
coal-slack, in which the combustion-chamber to complete the combustion
of the fuel was thought essential. By Wootten’s device, i.e., extending
the boiler out over the driving-wheels, a much greater width of
fire-box was secured, but the height of the locomotive was considerably
increased. It cannot be definitely stated just how high the centre of
the locomotive boiler may be placed above the track without prejudice
to safety in running at high speeds, but it has not generally been
thought best to lift that centre more than about 9½ feet above the
tops of rails, and this matter has been held clearly in view in the
development of the wide fire-box type of locomotive boilers.
Like every other new form of machine, the Wootten boiler developed some
weak features, although there was no disappointment in its steaming
capacity. It will be noticed in the figure that the plates forming that
part of the boiler over the fire-box show abrupt changes in curvature
which induced ruptures of the stay-bolts and resulted in other
weaknesses. This boiler passed through various stages of development,
till at the present time Figs. 22 and 23 show its most advanced form,
which is satisfactory in almost or quite every detail. The sudden
changes in direction of the plates in the first Wootten example have
been displaced by more gradual and easy shapes. Indeed there are few
features other than those which characterize simple and easy boiler
construction. The enormous grate area is evident from the horizontal
dimensions of the fire-box, which are about 120 inches in length by
about 106 inches in breadth. The boiler has over 4000 square feet of
heating surface and carries about 200 pounds per square inch pressure
of steam. The combustion-chamber in front of the fire-box has been
reduced to a length of about 6 inches, just enough for the protection
of the expanded ends of the tubes. The barrel of the boiler in front of
the fire-box has a diameter of 80 inches and a length of about 15 feet.
The grate area is not far from 100 square feet. The improvements which
have culminated in the production of this boiler are due largely to Mr.
Samuel Higgins of the Lehigh Valley Road.
[Illustration: FIG. 22.]
[Illustration: FIG. 23.]
=293. Locomotives with Wootten Boilers.=—Fig. 24 exhibits a
consolidation freight locomotive of the Lehigh Valley Railroad, having
the boiler shown in Figs. 22 and 23. This machine is one of the most
efficient and powerful locomotives produced at the present time. The
locomotive shown in Fig. 25 has a record. It is one used on the fast
Reading express service between Philadelphia and Atlantic City during
the season of the latter resort. It has run one of the fastest schedule
trains in the world and has attracted attention in this country and
abroad. Its type is called the Atlantic and, as the view shows, it is
fitted with the Wootten improved type of boiler. It will be noticed
that the wide fire-box does not reach out over the rear drivers, but
over the small trailing-wheels immediately behind them. This is a
feature of wide locomotive fire-box practice at the present time to
which recourse is frequently had. There is no special significance
attached to the presence of the small trailing-wheels except as a
support for the rear end of the boiler, their diameters being small
enough to allow the extension of the fire-box over them without unduly
elevating the centre of the boiler.
[Illustration: FIG. 24.]
The cylinders of these and many other locomotives are known as the
Vauclain compound. In other words, it is a compound locomotive, there
being two cylinders, one immediately over the other, on each side. The
diameter of the upper cylinder is much less than that of the lower.
The steam is first admitted into the small upper cylinder and after
doing its work there passes into the lower or larger cylinder, where
it does its work a second time with greater expansion. By means of this
compound or double-cylinder use of the steam a higher rate of expansion
is secured and a more uniform pull is exerted upon the train, the first
generally contributing to a more economical employment of the steam,
which in turn means a less amount of fuel burned for a given amount of
tractive work performed.
[Illustration: FIG. 25.]
In the early part of November, 1901, an engine of this type hauling a
train composed of five cars and weighing 235 tons made a run of 55.5
miles between Philadelphia and Atlantic City at the rate of 71.6 miles
per hour, the fastest single mile being made at a rate of a little less
than 86 miles per hour.
The power being developed by these engines runs as high as 1400 H.P. at
high speeds and 2000 H.P. at the lower speeds of freight trains.
The chief economic advantage of these wide fire-box machines lies in
the fact that very indifferent grades of fuel may be consumed. Indeed
there are cases where fuel so poor as to be unmarketable has been used
most satisfactorily. With a narrow and small fire-box a desired high
rate of combustion sometimes demands a draft strong enough to raise
the fuel over the grate-bars. This difficulty is avoided in the large
fire-box, where sufficient combustion for rapid steaming is produced
with less intensity of blast.
=294. Recent Improvements in Locomotive Design.=—Concurrently with the
development of the Wootten type of boiler, other wide fire-box types
have been brought to a high state of excellence. In reality general
locomotive progress within the past few years has been summed up by Mr.
F. J. Cole as follows:
(_a_) The general introduction of the wide fire-box for burning
bituminous coal.
(_b_) The use of flues of largely increased length.
(_c_) The improvements in the design of piston-valves and their
introduction into general use.
(_d_) The recent progress made in the use of tandem compound cylinders.
[Illustration: FIG. 26.]
The piston-valve, to which reference is made, is a valve in the shape
of two pistons connected by an enlarged stem or pipe the entire length
of the double piston, the arrangement depending upon the length of
steam-cylinder or stroke; it may be 31 or 32 inches. This piston-valve
is placed between the steam-cylinder and the boiler, and is so moved
by eccentrics attached to the driving-wheel axles through the medium
of rocking levers and valve-stems as to admit steam to the cylinder at
the beginning of the stroke and allow it to escape after the stroke is
completed. Fig. 26 shows a section through the centre of one of these
piston-valves. It will be noticed that the live steam is admitted
around a central portion of the valve, and that the steam escapes
through the exhaust-passages at each end of the piston-valve. This type
of valve is advantageous with high steam pressures for the reason that
its “blast,” i.e., the steam pressure, does not press it against its
bearings as is the case with the old type of slide-valve, the wear of
which with modern high steam pressures would be excessive, although
under more recent slide-valve design this objection does not hold.
[Illustration: FIG. 27.]
=295. Compound Locomotives with Tandem Cylinders.=—The tandem
compound locomotive, as recently built, is a locomotive in which
the high-pressure cylinder is placed immediately in front of the
low-pressure cylinder and in line with it. In the Vauclain type it
is necessary to have a piston-rod for each of the two cylinders, one
above the other, each taking hold of the same cross-head. In the tandem
arrangement with the two cylinders each in line, but one piston-rod is
required. An example of a locomotive with this tandem arrangement of
compound cylinders will be shown farther on.
[Illustration: FIG. 28.]
Figs. 27 and 28 show two sections, one transverse and one longitudinal,
of a type of large fire-box boiler built by the American Locomotive
Works at Schenectady. The diameter of the barrel of the boiler in front
of the fire-box is about 5 feet 8 inches, while the clear greatest
width of the fire-box is 5 feet 4½ inches. The length of the latter is
8 feet 7 inches, making a total grate area in this particular instance
of over 45 square feet. There are 338 2-inch tubes, each 16 feet in
length. The total length over all of the boiler is 31 feet ½ inch. The
result of such a design is an arrangement by which a large grate area
is secured and a corresponding high rate of combustion without a too
violent draft. In designing locomotive boilers for bituminous coal
one square foot of grate area is sometimes provided for each 60 to 70
square feet of heating surface in the tubes.
[Illustration: FIG. 29.]
=296. Evaporative Efficiency of Different Rates of Combustion.=—In the
development of this particular class of locomotive boilers it is to be
remembered that as a rule the highest rates of combustion frequently
mean a decreased evaporation of water at boiler pressure per pound of
fuel. Modern locomotives may burn over 200 pounds of coal per square
foot of grate area per hour, and in doing so the evaporation may be
less than 5 pounds of water per pound of fuel. On the other hand, when
the coal burned does not exceed 50 pounds per square foot of grate area
per hour, as much as 8 pounds of water may be evaporated for each pound
of coal. It is judicious, therefore, to have large grate area, other
things being equal, in order that the highest attainable efficiency in
evaporation may be reached.
=296a. Tractive Force of a Locomotive.=—The tractive force of a
locomotive arises from the fact that one solid body cannot be moved
over another, however smooth the surface of contact may be, without
developing the force called resistance of friction. This resistance is
measured by what is called the coefficient of friction, determined only
by experiment. The resistance of friction and this coefficient will
depend both upon the degree of smoothness of the surface of contact
and on its character. If surfaces are lubricated, as in the moving
parts of machinery, the force of friction is very much decreased, but
in the absence of that lubricant it will have a much higher value.
The coefficient of friction is a ratio which denotes the part of the
weight of the body moved which must be applied as a force to that body
in order to put it in motion against the resistance of friction. In
the case of lubricated surfaces this ratio may be as small as a few
hundredths. In the case of locomotive driving-wheels and the track on
which they rest this value is usually taken at .2 to .25.
There are times when it is desirable to increase the resistance of
friction between locomotive drivers and the rails. For this purpose a
simple device, called the sand-box, is frequently placed on the top of
a locomotive boiler with pipes running down from it so as to discharge
the sand on the rails immediately in front of the drivers. The sand is
crushed under the wheels and offers an increased resistance to their
slipping.
The tractive force of a locomotive may also be computed from the
pressure of steam against the pistons in the steam-cylinders. If the
indicated horse-power in the cylinder be represented by H.P., and
if all frictional or other resistance between the cylinder and the
draw-bar be neglected, the following equality will hold:
Draw-bar pull × speed of train in miles }
per hour × 5280 } = H.P. × 33,000 × 60.
If _S_ = speed in miles per hour, and if _T_ = draw-bar pull, then the
preceding equality gives
375 × H.P.
_T_ = ----------.
_S_
This value of the “pull” must be diminished by the friction of the
locomotive as a machine, by the rolling resistance of the trucks and
tender, and by the atmospheric resistance of the locomotive as the head
of the train. Prof. Goss proposes the following approximate values for
these resistances in a paper read before the New England Railroad Club
in December, 1901.
A number of tests have shown that a steam pressure of 3.8 pounds per
square inch on the piston is required to overcome the machine friction
of the locomotive. Hence if _d_ is the diameter of the piston in
inches, _L_ the piston-stroke in feet, and _D_ the diameter of driver
in feet, while _f_ is that part of the draw-bar pull required to
overcome machine friction, the following equation will hold:
π_d_²
_f_.π_D_ = 3.8 -----× 2_L_ × 2.
4
_d²L_
∴ _f_ = 3.8 ------.
_D_
Again, if _W_ be the rolling load in tons on tender and trucks
(excluding that on drivers), and if _r_ be that part of the draw-bar
pull required to overcome the rolling resistance due to _W_, then
experience indicates that approximately, in pounds,
( _S_ )
_r_ = (2 + --- )_W_.
( 6 )
As before, _S_ is the speed in miles per hour.
Finally, if _h_ be that part of the draw-bar pull in pounds required to
overcome the head resistance (atmospheric) of the locomotive, there may
be written approximately
_h_ = .11_S_².
The actual draw-bar pull in pounds available for moving the train will
then be
375 H.P. _d_²_L ( S_ )
_t = T - f - r - h_ = -------- - 3.8------ - _W_(2 + ----) - .11_S_².
_S D_ ( 6 )
The maximum value of _t_ should be taken as one fourth the greatest
weight on drivers.
If _H_ is the total heating surface in square feet, and if 12 pounds of
water be evaporated per square foot per hour, while 28 pounds of steam
are required per horse-power per hour, then
12_H_ 375H.P. 161_H_
H.P. = ----- and -------- = ------.
28 _S S_
Hence
161_H d²L_ ( _S_ )
_t_ = ----- - 3.8----- - _W_(2 + ----) - .11_S²_.
_S D_ ( 6 )
The actual draw-bar pull in pounds may then be computed by this formula.
Some recent tests of actual trains (both heavy and light) on the N.
Y. C. & H. R. R. R. between Mott Haven Junction and the Grand Central
Station, New York City, a distance of 5.3 miles, by M. Bion J. Arnold,
by means of a dynamometer-car, gave the actual average draw-bar pull
per ton of 2000 pounds as ranging from 12 to 25 pounds going in one
direction and 12.1 to 24 pounds in the opposite direction. There were
eight tests in each direction, and the greatest speed did not exceed 30
miles per hour.
As the diameter of the driver appears in the preceding formulæ, it may
be well to state that an approximate rule for that diameter is to make
it as many inches as the desired maximum speed in miles per hour, i.e.,
70 inches for 70 miles, or 80 inches for 80 miles, per hour.
=297. Central Atlantic Type of Locomotive.=—Fig. 29 represents what is
termed the Central Atlantic type (single cylinder) of engine, which
is used for hauling most of the fast passenger trains on the New York
Central and Hudson River Railroad. The characteristics of boiler and
fire-box are such as are shown in Figs. 27 and 28.
The cylinders are 21 inches internal diameter, and the stroke is 26
inches. The total grate area is 50 square feet, and the total heating
surface 3500 square feet. The total weight of the locomotive is 176,000
pounds, with 95,000 on the drivers. It will be observed that the total
weight of locomotive per square foot of heating surface is scarcely
more than 650 pounds, which is a low value. The boiler pressure
carried may be 200 pounds per square inch or more. The tractive force
of this locomotive may be taken at 24,700 pounds. There is supplied
to these engines, among others, what is called a traction-increasing
device. This traction-increaser is nothing more nor less than a
compressed-air cylinder secured to the boiler, so that as its piston
is pressed outward, i.e., downward, it carries with it a lever, the
fulcrum of which is on the equalizing-lever of the locomotive frame,
the other or short end of the lever being attached to the main bar of
the frame itself. This operation redistributes the boiler-load on the
frame, so as to increase that portion which is carried by the drivers.
This has been found to be a convenient device in starting trains and
on up grades. In the present instance the traction-increaser may be
operated so as to increase the load on the drivers by about 12,000
pounds. It is not supposed to be used except when needed under the
circumstances indicated.
[Illustration: FIG. 30.]
A number of indicator-cards taken from the steam-cylinders of these
engines hauling the Empire State Express and other fast passenger
trains on the Hudson River Division of the N. Y. C. & H. R. R. R.,
show that with a train weighing about 208 tons while running at a
speed of 75 miles per hour 1323 H.P. was developed. Fig. 30 shows
these indicator diagrams. With a train weighing 685 tons 1452 H.P. was
indicated at a speed of 63 miles per hour.
=298. Consolidation Engine, N. Y. C. & H. R. R. R.=—One of the heaviest
wide fire-box compound consolidation engines recently built for the New
York Central freight service is shown in Fig. 31. It will be noticed
that there is but one cylinder on each side of the locomotive, and
that they are of different diameters. One of these cylinders, 23 inches
inside diameter, is a high-pressure cylinder, and the other, 35 inches
inside diameter, is a low-pressure cylinder, the stroke in each case
being 34 inches. The total grate area is 50.3 square feet, the fire-box
being 8 feet long by 6 feet 3 inches wide. The total heating surface
is 3480 square feet. The diameter of the barrel of the boiler at the
front end is 72 inches, and the diameter of the drivers 63 inches. The
pressure of steam in the boiler is 210 pounds per square inch. The
total weight of the locomotive is 194,000 pounds, of which 167,000
rests upon the drivers. These engines afford a maximum tractive force
of 37,900 pounds. This engine is typical of those used for the New York
Central freight service. They have hauled trains weighing nearly 2200
tons over the New York Central road.
[Illustration: FIG. 31.]
=299. P., B. & L. E. Consolidation.=—The consolidation locomotive shown
in Fig. 32 is a remarkable one in that it was for a time the heaviest
constructed, but its weight has since been exceeded by at least two of
the Decapod type built for the Sante Fé company. It was built at the
Pittsburg works of the American Locomotive Company for the Pittsburg,
Bessemer and Lake Erie Railroad to haul heavy trains of iron ore. The
total weight is 250,300 pounds, of which the remarkable proportion of
225,200 is carried by the drivers. The tender carries 7500 gallons
of water, and the weight of it when loaded is 141,100 pounds, so that
the total weight of engine and tender is 391,400 pounds. The average
weight of engine and tender therefore approaches 7000 pounds per
lineal foot. This is not a compound locomotive, but each cylinder has
24 inches inside diameter and 32 inches stroke, the diameter of the
driving-wheels being 54 inches. The boiler carries a pressure of 220
pounds, and the tractive force of the locomotive is 63,000 pounds.
[Illustration: FIG. 32.]
A noticeable feature of this design, and one which does not agree with
modern views prompting the design of wide fire-boxes, is its great
length of 11 feet and its small width of 3 feet 4¼ inches. There are
in the boiler 406 2¼-inch tubes, each 15 feet long, the total heating
surface being 3805 square feet.
=300. L. S. & M. S. Fast Passenger Engine.=—The locomotive shown in
Fig. 33 is also a remarkable one in some of its features, chief among
which is the 19 feet length of tubes. It was built at the Brooks works
of the American Locomotive Company for the Lake Shore and Michigan
Southern Railroad. The total weight of engine is 174,500 pounds, of
which 130,000 pounds rests upon the drivers. The rear truck carries
23,000 pounds and the front truck 21,500 pounds. This is not a compound
engine. The cylinders have each an inside diameter of 20½ inches, and
28 inches stroke. As this locomotive is for fast passenger traffic, the
driving-wheels are each 80 inches in diameter, and the driving-wheel
base is 14 feet. The fire-box is 85 × 84 inches, giving a grate area
of 48½ square feet and a total heating surface of 3343 square feet.
There are 285 2¼-inch flues, each 19 feet long. The tender carries 6000
gallons of water. Cast and compressed steel were used in this design
to the greatest possible extent, and the result is shown in that the
weight divided by the square feet of heating surface is 52.18 pounds.
[Illustration: FIG. 33.]
=301. Northern Pacific Tandem Compound Locomotive.=—The diagram shown
in Fig. 34 exhibits the outlines and main features of a tandem compound
locomotive to which allusion has already been made. It was built at
Schenectady, New York, in 1900, for the Northern Pacific Railroad, and
was intended for heavy service on the mining portions of that line.
The diameters of the high- and low-pressure cylinders are respectively
each 15 and 28 inches, with a stroke of 34 inches, while the boiler
pressure is 225 pounds per square inch. The total weight of the machine
is 195,000 pounds and the weight on the drivers 170,000 pounds, the
diameter of the drivers being 55 inches. As the figure shows, it
belongs to the consolidation type. The fire-box is 10 feet long by 3.5
feet wide, giving a grate area of 35 square feet, with which is found
a total heating surface of 3080 square feet. There are 388 2-inch
tubes, each 14 feet 2 inches long. These engines are among the earliest
compound-tandem type and have been very successful. Other locomotives
of practically the same general type have been fitted with a wide
fire-box, 8 feet 4 inches long by 6 feet 3 inches wide, with the grate
area thus increased to 52.3 square feet.
[Illustration: FIG. 34.]
=302. Union Pacific Vauclain Compound Locomotive.=—The next example
of modern locomotive is the Vauclain compound type used on the Union
Pacific Railroad. It is a ten-wheel passenger engine and one of a
large number in use. The weight on the drivers is 142,000 pounds,
and the total weight of the locomotive is about 185,000 pounds. The
high-pressure cylinder has an inside diameter of 15½ inches, while the
low-pressure cylinder has a diameter of 26 inches. The stroke is 28
inches and the diameter of the driving-wheels 79 inches. On the Union
Pacific Railroad the diameter of the driving-wheel varies somewhat with
the grades of the divisions on which the engines run.
[Illustration: FIG. 35.]
In some portions of the country, as in Southern California, oil has
come into quite extended use for locomotive fuel.
=303. Southern Pacific Mogul with Vanderbilt Boiler.=—The locomotive
shown in Fig. 36 belongs to the Mogul type, having three pairs
of driving-wheels and one pair of pilots. It is fitted with the
Vanderbilt boiler adapted to the use of oil fuel. The locomotives of
which this is an example were built for the Southern Pacific Company,
and they have performed their work in a highly satisfactory manner.
They are not particularly large locomotives as those matters go at the
present day, as they carry about 135,000 pounds on the drivers and
22,000 pounds on the truck, giving a total weight of 157,000 pounds.
The characteristic feature of the machine is its adaptation to the
burning of oil, which requires practically no labor in firing, although
the services of a fireman must still be retained.
[Illustration: FIG. 36.]
=304. The “Soo” Decapod Locomotive.=—It has been seen that the results
of Trevethick’s early efforts was a crude and simple machine, with what
might be termed, in courtesy to that early attempt, a single pair of
drivers. Subsequently, as locomotive evolution took place, two pairs
of drivers coupled with the horizontal connecting-rod were employed.
Then the Mogul with the three pairs of coupled drivers was used, and
at or about the same time the consolidation type with four pairs of
coupled drivers was found adapted in a high degree to the hauling of
great freight trains. The last evolution in driving-wheel arrangement
is exhibited in Fig. 37. It belongs to what is called the Decapod type.
As a matter of fact, five pairs of coupled driving-wheels have been
occasionally used for a considerable number of years, but this engine
is the Decapod brought up to the highest point of modern excellence.
As shown, it uses steam by the Vauclain compound system, the small or
high-pressure cylinder being underneath the low-pressure cylinder. They
have been built by the Baldwin Locomotive Works for the Minneapolis,
St. Paul and Sault Ste. Marie Railroad Company, on what is called the
“Soo Line.” It has given so much satisfaction that more of this type
but of greater weight are being built for the same company. This engine
was limited to a total weight of 215,000 pounds, with 190,000 pounds on
the drivers.
[Illustration: FIG. 37.]
[Illustration: FIG. 38.]
[Illustration: FIG. 39.]
[Illustration: FIG. 40.]
=305. The A., T. & S. F. Decapod, the Heaviest Locomotive yet
Built.=—The heaviest locomotive yet constructed, consequently occupying
the primacy in weight, is that shown in Fig. 38. It is a Decapod
operated with others of its type by the A., T. & S. F. Company near
Bakersfield, California. It is a tandem compound coal-burner, as shown
by the illustration, the high-pressure cylinder being in front of the
low-pressure. The dimensions of cylinders are 19 and 32 × 32 inches
stroke, and the driving-wheels are 57 inches in diameter. The total
height from the top of stack down to the rail is 15 feet 6 inches,
while the height of the centre of the boiler above the rails is 9 feet
10 inches. Figs. 39 and 40 show some of the main boiler and fire-box
dimensions. There are 463 2¼-inch tubes, each 19 feet long. The total
heating surface is 5390 square feet, about one eighth of an acre, the
length of the fire-box being 108 inches and the width 78 inches. The
heating surface in the tubes is 5156 square feet, and in the fire-box
210.3 square feet; the grate surface having an area of 58.5 square
feet. The boiler is designed to carry a working pressure of 225 pounds
per square inch, the boiler-plates being ¹⁵/₁₆ inch, ⁹/₁₆ inch, and ⅞
inch thick, according to location. As shown by the illustrations, the
boiler is what is termed an extended wagon-top with wide fire-box. The
total weight of the locomotive itself is 267,800 pounds, while the
weight on the driving-wheels is 237,800 pounds, making 47,560 pounds
on each axle. The tractive force of this locomotive is estimated to be
over 62,000 pounds.
=306. Comparison of Some of the Heaviest Locomotives in Use.=—The
following table gives a comparison of the heaviest locomotives thus
far built, as taken from the _Railroad Gazette_ for January 31, 1902,
revised to September 1, 1902.
COMPARISON OF HEAVIEST LOCOMOTIVES.
---------------------+----------------+-------------+-------------
| Atchison, | Pittsburg, | Union
| Topeka | Bessemer & | Railroad.
| & Santa Fé. | Lake Erie. |
---------------------+----------------+-------------+-------------
Name of builder | Baldwin | Pittsburg | Pittsburg
Size of cylinders |19 & 32 × 32 in.|24 × 32 in. |23 × 32 in.
Total weight | 267,800 lbs. |250,300 lbs. |230,000 lbs.
Weight on drivers | 237,800 lbs. |225,200 lbs. |208,000 lbs.
Driving-wheels, diam.| 57 in. | 54 in. | 54 in.
Heating surface | 5,390 sq. ft. |3,805 sq. ft.|3,322 sq. ft.
Grate area | 58.5 sq. ft. |36.8 sq. ft. |33.5 sq. ft.
---------------------+----------------+-------------+-------------
| Illinois | Lehigh
| Central. | Valley.
---------------------+----------------+----------------
Name of builder | Brooks | Baldwin
Size of cylinders | 23 × 30 in. | 18 & 30 × 30 in.
Total weight | 232,200 lbs. | 225,082 lbs.
Weight on drivers | 193,200 lbs. | 202,232 lbs.
Driving-wheels, diam.| 57 in. | 55 in.
Heating surface | 3,500 sq. ft. | 4,104 sq. ft.
Grate area | 37.5 sq. ft. | 90 sq. ft.
---------------------+----------------+----------------
These instances of modern locomotive construction are impressive,
especially when considered in contrast with the type of engine in use
not more than fifty years ago. They indicate an almost incredible
advance in railroad transportation, and they account for the fact that
a bushel of wheat can be brought overland at the present time from
Chicago to New York City, a distance of 900 miles, for about one third
of the lowest charge for delivering a valise from the Grand Central
Station in the city of New York to a residence within a mile of it.
PART V.
_THE NICARAGUA ROUTE FOR A SHIP-CANAL._
=307. Feasibility of Nicaragua Route.=—The feasibility of a ship-canal
between the two oceans across Nicaragua has been recognized almost
since the discovery of Lake Nicaragua in 1522 by Gil Gonzales de Avila,
who was sent out from Spain to succeed Balboa, after the execution of
the latter by Pedro Arias de Avila at Acla on the Isthmus of Panama.
=308. Discovery of Lake Nicaragua.=—Gil Gonzales set sail from the
Bay of Panama in January of that year northward along the Pacific
coast as far as the Gulf of Fonseca. He landed there and proceeded to
explore the country with one hundred men, and found what he considered
a great inland sea, as we now know, about 14 miles from the Pacific
Ocean at the place of least separation. The country was inhabited,
and he found a native chief called Nicarao, who was settled with his
people at or near the site of the present city of Rivas. As he found
it a goodly country, fertile and abounding in precious metals, he
immediately proceeded to take possession of it for his sovereign, but
the Spanish explorer was sufficiently gracious to the friendly chief
to name Lake Nicaragua after him. From that time the part of Nicaragua
in the vicinity of the lake received much attention, and the Spaniards
made conquest of it without delay. Among those who were the earliest
visitors was a Captain Diego Machuca, who, with two hundred men under
his command, explored Lake Nicaragua in 1529 and constructed boats
on it, a brigantine among them. He seems to have been the first one
who entered and sailed down the Desaguadero River, now called the San
Juan, and one of the rapids in the upper portion of the river now
bears his name. He pursued his course into the Caribbean Sea and sailed
eastward to the Isthmus of Panama.
[Illustration: Map of American Isthmus, showing Proposed Canal Routes.]
=309. Early Maritime Commerce with Lake Nicaragua.=—Subsequently
sea-going vessels passed through the San Juan River in both directions
and maintained a maritime trade of some magnitude between the shores
of Lake Nicaragua and Spain. Obviously these vessels must have been
rather small for ocean-going craft, unless there was more water in the
San Juan River in those early days than at present. There are some
obscure traditions of earthquakes having disturbed the bed of the river
and made its passage more difficult by reducing the depth of water in
some of the rapids; but these reports are little more than traditionary
and lack authoritative confirmation. It is certain, however, that the
marine traffic, to which reference has been made, was maintained for
a long period of years, its greatest activity existing at about the
beginning of the seventeenth century. It was in connection with this
traffic probably that the city of Granada at the northwestern extremity
of the lake was established, perhaps before 1530.
=310. Early Examination of Nicaragua Route.=—Although the apparently
easy connection between the Caribbean Sea and Lake Nicaragua, together
with the proximity of the latter to the Pacific coast, at once
indicated the possibility of a feasible water communication between
the two oceans, probably no systematic investigation to determine a
definite canal line was made until that undertaken by Manuel Galisteo
in 1779 under the instruction of Charles III., who was then on the
throne of Spain. Galisteo made a report in 1781 that Lake Nicaragua
was 134 feet higher than the Pacific Ocean, and that high mountains
intervened between the lake and the ocean, making it impracticable
to establish a water communication between the two. In spite of the
discouragement of this report a company was subsequently formed under
the patronage of the crown to construct a canal from Lake Nicaragua
along the Sanoa River to the Gulf of Nicoya, but nothing ever came of
the project.
=311. English Invasion of Nicaragua.=—The country was invaded in 1780
by an English expedition sent out from Jamaica under Captain Horatio
Nelson, who subsequently became the great admiral. He proceeded up
the San Juan River, and after some fighting captured by assault Fort
San Juan at Castillo Viejo. Nelson and his force, however, were ill
qualified to take care of themselves in that tropical country where
drenching rains were constantly falling, and he was therefore obliged
to abandon his plan of taking possession of Lake Nicaragua and returned
instead to Jamaica. The tropical fevers induced by exposure reduced
the crew of his own ship, two hundred in number, to only ten after his
return to Jamaica, and he himself nearly lost his life by sickness.
=312. Atlantic and Pacific Ship-canal Company.=—Subsequently to this
period the Nicaragua route attracted more or less attention until Mr.
E. G. Squier, the first consul for the United States in Nicaragua,
negotiated a treaty between the two countries for facilitating the
traffic from the Atlantic to the Pacific Ocean by means of a ship-canal
or railroad in the interest of the Atlantic and Pacific Ship-canal
Company, composed of Cornelius Vanderbilt, Joseph L. White, Nathaniel
Wolfe, and others. It was at this time that the Nicaragua route became
prominent as a line of travel between New York and San Francisco.
Ships carried passengers and freight from New York to Greytown, then
trans-shipped them to river steamboats running up the San Juan River
and across the southerly end of the lake to a small town called La
Virgin, whence a good road for 14 miles overland led to the Pacific
port of San Juan del Sur. Pacific coast steamships completed the trip
between the latter port and San Francisco.
=313. Survey and Project of Col. O. W. Childs.=—This traffic stimulated
the old idea of a ship-canal across the Central American isthmus on the
Nicaragua route to such an extent that Col. O. W. Childs, an eminent
civil engineer, was instructed by the American Atlantic and Pacific
Ship-canal Company to make surveys and examinations for the project
of a ship-canal on that route. The results of his surveys, made in
1850-52, have become classic in interoceanic canal literature. He
concluded that the most feasible route lay up the San Juan River from
Greytown to Lake Nicaragua, across that lake, and down the general
course of the Rio Grande on the west side of Nicaragua to Brito on the
Pacific coast. This is practically identical with the route adopted by
the Isthmian Canal Commission now (1902) being discussed in Congress.
=314. The Project of the Maritime Canal Company.=—The project planned
by Col. Childs, like those which preceded it, had no substantial issue,
but the general subject of an isthmian canal across Nicaragua was, from
that time, under almost constant agitation and consideration more or
less active until the Maritime Canal Company of Nicaragua was organized
in February, 1889, under concessions secured from the governments
of Nicaragua and Costa Rica by Mr. A. G. Menocal. This company made
a careful examination of all preceding proposed routes, and finally
settled upon a plan radically different in some respects from any
before considered. The Caribbean end of the canal was located on the
Greytown Lagoon west of Greytown. From that point the line followed
up the valley of the Deseado River and cut across the hills into the
valley of the San Juan above its junction with the San Carlos. A dam
was to be constructed across the San Juan River at Ochoa, below the
mouth of the San Carlos, so as to bring the surface of Lake Nicaragua
down to that point. From its junction with the San Juan River the canal
line followed that river to the lake, across the latter to Las Lajas,
and thence down the Rio Grande to the Pacific coast at Brito. It was
contemplated under this plan to carry the lake level to a point called
La Flor, 13.5 miles west of the lake, and drop down to the Pacific
from that point by locks suitably located. After partially excavating
the canal prism for about three quarters of a mile from the Greytown
Lagoon, constructing a line of railroad up the Deseado valley, as well
as a telegraph line, and doing certain other work preparatory to the
actual work of construction, the Maritime Canal Company became involved
in financial difficulties and suspended operations without again
resuming them.
[Illustration: Breakwater of the Maritime Canal Company. The closed
former entrance to Greytown harbor is shown on the left.]
=315. The Work of the Ludlow and Nicaragua Canal Commissions.=—In
1895 and again in 1897 two commissions were appointed by the
President of the United States to consider the plans and estimates
of the Maritime Canal Company in the one case, and the problem of a
ship-canal on the Nicaragua route in the latter. Neither of these
commissions, however, had the funds at its disposal requisite for a
full and complete consideration of the problem. In 1899, therefore,
the Isthmian Canal Commission was created by Act of Congress, and
appointed by the President of the United States, to determine the most
feasible and practical route across the Central American isthmus for a
canal, together with the cost of constructing it and placing it under
the control, management, and ownership of the United States. This
commission consisted of nine members, and included civil and military
engineers, an officer of the navy, an ex-senator of the United States,
and a statistician. It was the province and duty of this commission to
make examinations of the entire isthmus from the Atrato River in the
northwestern corner of South America to the western limits of Nicaragua
for the purpose of determining the most feasible and practical route
for a ship-canal between those territorial limits. This brings the
general consideration of the isthmian canal question to the Nicaragua
route in particular, to which alone attention will be directed in this
part.
=316. The Route of the Isthmian Canal Commission.=—The Isthmian Canal
Commission adopted a route practically following the San Juan River
from near Greytown to the lake, across the latter to Las Lajas on
its westerly shore, and thence up the course of the Las Lajas River,
across the continental divide into the Rio Grande valley, and down the
latter to Brito at the mouth of the Rio Grande on the Pacific coast.
As has already been stated, this is practically the line adopted by
Col. Childs almost exactly fifty years ago. It is also essentially the
route adopted by the Nicaragua Canal Commission appointed in 1897,
and which completed its operations immediately prior to the creation
of the Isthmian Canal Commission. The amount of work performed in the
field under the direction of the commission can be realized from the
statement that twenty working parties were organized in Nicaragua with
one hundred and fifty-nine civil engineers and other assistants, and
four hundred and fifty-five laborers.
=317. Standard Dimensions of Canal Prism.=—By the Act of Congress
creating it, the latter commission was instructed to consider plans
and estimates for a canal of sufficient capacity to accommodate the
largest ships afloat. In order to meet the requirements of those
statutory instructions the commission decided to adopt 35 feet as the
minimum depth of water in the canal throughout its entire length from
the deep water of one ocean to that of the other, wherever the most
feasible and practical route might be located, the investigations of
the commission having shown that the final location to be selected must
narrow down to a choice between the Panama and the Nicaragua routes.
It was further decided by the commission that the standard width of
excavation at the bottom of the canal should be 150 feet, with 500 feet
for the ocean entrances to harbors, and 800 feet in those harbors.
Greater widths than that of the bottom of standard excavations were
also adopted for river and lake portions. The slopes of the sides of
the excavation were determined to be 1 vertical on 1½ horizontal for
firm earth, but as flat as 1 vertical on 3 or even 6 horizontal for
soft mud or silt in marshy locations. In rock cutting below water the
sides of the excavation would be vertical, but as steep as 4 vertical
on 1 horizontal above water.
[Illustration]
[Illustration: Standard Sections adopted by the Isthmian Canal
Commission.]
The longest ship afloat at the present time (1902) is the Oceanic of
the White Star Line, and its length is about 704 feet. The widest
ships, i.e., the ships having the greatest beam, are naval vessels,
and at the present time none has a greater beam than about 77 feet. In
order to afford accommodation for further development in both length
and beam of ships without leading to extravagant dimensions, the
commission decided to provide locks having a usable length of 740 feet
with a clear width of 84 feet. These general dimensions meet fully the
requirements of the law, and were adopted for plans and estimates on
both the Panama and Nicaragua routes.
=318. The San Juan Delta.=—The entire Central American isthmus
is volcanic in character, and this is particularly true of the
country along the Nicaragua route with the exception of the lowlands
immediately back of the ocean shore line in the vicinity of Greytown.
From the latter point to Fort San Carlos, where the San Juan River
leaves the lake, is approximately 100 miles. With the exception of
the 15 miles nearest to the seacoast the San Juan River runs mostly
through a rugged country with high hills densely wooded on either
side. The soil is mostly heavy clay, although the bottom of the valley
immediately adjacent to the river is largely of sandy silt with some
mixture of clay. Between the hills back of Greytown and the seacoast
the country is almost a continuous morass covered with coarse grasses
and other dense tropical vegetation, but with a number of small
isolated hills projecting up like islands in the surrounding marsh,
and interspersed with numerous lagoons. All this flat country has the
appearance of forming a delta through which a number of mouths of the
San Juan River find their way. One of these, called the Lower San Juan,
empties into the Greytown Lagoon, but the main mouth of the San Juan,
called the Colorado, branches from the main river at the point where
the Lower San Juan begins, about 13 or 14 miles from the ocean. The
Colorado itself is composed of two branches, and at the place where it
empties into the sea there are a number of long narrow lagoons parallel
to the seashore, appearing to indicate comparatively recent shore
formation. Again, a small river called the Rio San Juanillo leaves the
main river 3 or 4 miles above the junction of the lower San Juan and
the Colorado, and pursues a meandering course through the low marshy
grounds back of Greytown, and finally again joins the Lower San Juan
near the town. This marshy lowland is underlaid by and formed largely
of dark-colored sand brought down mostly from the volcanic mountains of
Costa Rica by two rivers, the San Carlos and the Serapiqui, the former
joining the San Juan about 44 miles and the latter about 23 miles from
the sea.
[Illustration: Greytown Lagoon (formerly Greytown Harbor), showing
Greytown in the Distance.]
=319. The San Carlos and Serapiqui Rivers.=—Both those Costa Rican
rivers are subject to sudden and violent floods, and they bring down
large quantities of this volcanic sand, the specific gravity of which
is rather low. The San Carlos bears the greater burden of this kind.
In fact its bed, even when not in a state of flood, is at many points
at least composed of moving sands. Both rivers are clear-water streams
except in high water stages. Below the junction of the San Carlos the
San Juan is necessarily in times of floods a large bearer of silt and
sand, but above that point it carries little or no sediment. There are
no streams of magnitude which join the San Juan between the lake and
the San Carlos.
=320. The Rapids and Castillo Viejo.=—About 54 miles from the ocean
are the Machuca Rapids, and from that point to a distance of about 75
miles from the ocean other rapids are found, the principal of which are
the Castillo and the Toro. The Castillo Rapids are at the point called
Castillo Viejo, where there is located an old Spanish fort on the top
of the high hill around the base of which the river flows. The town of
Castillo Viejo has a small population of perhaps 500 to 600 people.
It is a place with historical associations, to which reference has
already been made. It was here that Captain (afterwards Admiral) Nelson
captured the Spanish fort in 1780. It is a place of some importance
in connection with the river traffic in consequence of necessary
transhipment of freight and passengers to overcome the rapids.
=321. The Upper San Juan.=—The upper reaches of the San Juan within
about 20 miles of the lake are bordered with considerable marshy
ground. In the vicinity of its exit from the lake there is a wide strip
of soft marshy country around the entire southeastern shore.
=322. The Rainfall from Greytown to the Lake.=—The entire country
between Greytown and the lake is intensely tropical, and the vegetation
is characteristically dense. It is particularly so at Greytown, where
the total annual rainfall sometimes reaches as much as 300 inches.
It rains many times in a day, and nearly every day in the year. The
strong easterly and northeasterly trade winds, heavy-laden with the
evaporation from the tropical sea, meet the high ground in the vicinity
of Greytown and precipitate their watery contents in frequent and heavy
showers. The general course of the San Juan valley is a little north
of west or south of east, and the trade winds appear to follow the
course of the valley to the lake. The rainfall steadily decreases as
the seashore is left behind, so that at Fort San Carlos, the point of
exit of the river from the lake, the annual precipitation may vary from
75 to 100 inches. There is no so-called dry season between the lake and
the Caribbean Sea, although at Fort San Carlos the rainfall is so small
between the middle of December and the middle of May that that period
may perhaps be considered, relatively speaking, a dry season. It is
evident, therefore, that all the conditions are favorable to luxuriant
tropical growths over this entire eastern portion of the canal route,
and the coarse grasses, palms, and other tropical vegetation found in
it are indescribably dense. The same general observation is applicable
to the forest and undergrowth throughout the entire course of the river
from Greytown to Fort San Carlos. All of the high ground is heavily
timbered, with undergrowth so dense that no survey line can be run
until it is first completely cut out. That observation holds with added
force throughout the swampy country adjacent to the seashore. All the
heavy forest growth carries dense vines and innumerable orchids, which
so cover the trunks and branches of trees as in many places completely
to obscure them.
[Illustration: The Maritime Canal Company’s Canal Cut leading out of
Greytown Lagoon.]
=323. Lake-surface Elevation and Slope of the River.=—The lake surface
has an area of about 3000 square miles and varies in elevation with the
amount of rainfall in its basin from about 97 or 98 to perhaps 110 feet
above the ocean. The average elevation can probably be taken at about
104 feet above the sea. The length of the lake is about 103 miles,
with a greatest width of 45 miles. The area of its watershed is about
12,000 square miles. Inasmuch as the length of the San Juan River from
the ocean to the lake is but a little more than 100 miles, its average
fall is seen to be about 1 foot per mile. The greatest slope of the
river surface is at Castillo Rapids, where it falls about 6 feet in ⅜
of a mile. At the Machuca Rapids it falls about 4 feet in 1 mile. From
the foot of Machuca Rapids to the mouth of the San Carlos, a distance
of a little over 15 miles, the surface of the river falls about 1 foot
only. This pool, with practically no sensible current, is called Agua
Muerte, or Dead Water. The relatively great depth of this pool shows
conclusively that the upper San Juan, i.e., above the mouth of the San
Carlos, carries no silt, otherwise the pool would be filled; in other
words, that part of the San Juan River is not a sediment-bearer. The
slope of the river surface in the Toro Rapids, about 27 miles from the
lake, gives a fall of 7³/₁₀ feet in 1⁷/₁₀ miles.
=324. Discharges of the San Juan, San Carlos, and Serapiqui.=—In
times of heavy floods the San Carlos River may discharge as much as
100,000 cubic feet per second into the San Juan, but such floods have
a duration of a comparatively few hours only. Its low water-discharge
may fall below 3000 cubic feet per second. The maximum outflow of the
lake during a rainy season or a season of heavy rainfall probably never
exceeds about 70,000 cubic feet per second, but that rate of discharge
may continue for a number of weeks. The low water-discharge of the San
Juan above the mouth of the San Carlos may fall below 10,000 feet per
second, or 13,000 feet per second below the mouth of the San Carlos but
above that of the Serapiqui.
=325. Navigation on the San Juan.=—From what has been said of the
San Juan River it is evident that in times of low water no boats
drawing more than about 5 or 6 feet can navigate it, and most of the
river boats draw less than that amount. In times of low water no
boat can navigate the Lower San Juan drawing more than about 2½ to 3
feet of water. Nor, again, can the ordinary river boats pass up the
rapids at Castillo except at high water. It is necessary, therefore,
that the larger boats used on the river confine their trips on the
one hand between the mouth of the Colorado and Castillo, and on the
other between Castillo above the rapids to Fort San Carlos. It is the
custom, therefore, to transfer passengers and freight from boats below
the rapids at Castillo by a short tramway to other boats in waiting
above the rapids at that point. Boats pass up Machuca and Toro rapids
at practically all seasons, but sometimes with difficulty.
In order to meet the exigencies of low water in the Lower San Juan
a railroad called the Silico Lake Railroad, with 3 feet gauge, has
been constructed from a point opposite the mouth of the Colorado,
called Boca Colorado, to Lake Silico in the marshes back of Greytown,
a distance of about 6 miles. Light-draft boats connect Lake Silico
with Greytown for the transfer of passengers and freight. The type of
light-draft steamboat used on the San Juan River is the stern-wheel
pattern, so much used on the western rivers of this country, the
lower deck carrying the engines and boilers as well as freight, while
the upper deck, fitted with crude staterooms, furnishes a kind of
accommodation for passengers.
=326. The Canal Line through the Lake and Across the West Side.=—The
little town of Fort San Carlos on a point raised somewhat above the
lake where the San Juan River leaves the latter is the second place
on the entire river from Greytown where any population may said to be
found, and probably not more than 400 or 500 people even there. Its
position is on the north side of the river, at the extreme southeastern
end of the lake, commanding a fine view of the water and the country
bordering it in that vicinity. To the westward lie the Solentiname
Islands, a group a short distance to the north of which the sailing
line for the canal in the lake is located. After passing this group
of islands that line deflects a little toward the south, so that its
course westward is but a little north of west, straight to a point
near to and opposite Las Lajas on the westerly shore of the lake,
southwest from the large island on which Ometepe and Madeira are
located; indeed those two volcanic cones, the former still active,
constitute the entire island. The point called Las Lajas is at the
mouth of a small river of that name which discharges any sensible
amount of water only during the wet season; it is located not more
than 10 miles from Ometepe, and affords a most impressive view of that
perfect volcanic cone rising almost an exact mile above the water. The
general direction of the canal route is a little west of south from Las
Lajas on the lake to Brito on the ocean shore. The line follows the
Las Lajas about a mile and a half only of the 5 miles from the lake in
a southwesterly direction to the point where the continental divide
is crossed. The elevation of the divide at this place is about 145
feet only above sea-level. The line then descends immediately into the
valley of the Rio Grande and follows that stream to its mouth at Brito.
[Illustration: The Maritime Canal Company’s Railroad near Greytown.]
=327. Character of the Country West of the Lake.=—The country on the
west side of the lake exhibits a character radically different from
that on the easterly side, i.e., between the lake and the Caribbean.
It is a country in which much more population is found. While there
are no towns along the 17 miles of the route from Las Lajas to Brito,
the old city Rivas, containing perhaps 12,000 to 15,000 people, is
about 6 miles from Las Lajas, and the small towns of San Jorge, Buenos
Ayres, Potosi, as well as others, are in the same general vicinity.
Plantations of cacao and various tropical fruits abound, and there
is a large amount of land under cultivation. It is largely a cleared
country, so that far less dense forest areas are found.
There are two distinct seasons in the year, the wet and the dry, the
latter extending from about the middle of December to the middle of
May. The annual rainfall is extremely variable, but in the vicinity
of Rivas it may run from 30 or 40 to nearly 100 inches. The country
is of great natural beauty, and one which, under well-administered
governmental control, would afford many places of delightful
residence. The trade winds blow across the lake from east to west with
considerable intensity and great regularity. They produce a beneficial
effect upon the climate and render atmospheric conditions far more
agreeable than in that part of Nicaragua in the vicinity of Greytown.
It will be remembered that Rivas is the city where the American
filibuster Walker was taken prisoner by the Costa Ricans and
Nicaraguans and shot in 1857.
=328. Granada to Managua, thence to Corinto.=—At the northwestern end
of the lake is located the attractive city Granada, sometimes called
the “Boston of Nicaragua.” A reference to a map of Nicaragua will
show that a short distance north of Granada is the river Tipitapa,
which connects Lake Nicaragua with Lake Managua, the latter lying 18
miles to the northwest of the former. A railroad connects Granada
with the city of Managua, which is the capital of Nicaragua, running
on its way through the city of Masaya, chiefly noted for the volcano
of the same name located near by, and which has been subjected to a
most destructive eruption. The old lava-flow still shows its path of
destruction by a broad black mark extending many miles across the
country. A railroad connects Lake Managua at Momotombo with the Pacific
port of Corinto.
=329. General Features of the Route.=—It is thus seen that the proposed
route of the Nicaragua Canal lies first along the valley of the San
Juan River, then across the lake, cutting the continental divide west
of the latter at the low elevation of 145 feet above the sea, thence
following the valley of the Rio Grande to the Pacific Ocean at Brito.
From Greytown to Castillo the San Juan River is the boundary between
Nicaragua and Costa Rica, and concessions from both governments would
be necessary for that part of its construction. From Castillo to the
Pacific Ocean the route lies entirely in Nicaraguan territory, and the
only concession necessary for that portion of the line would be from
the government of Nicaragua. From Castillo to and around the southern
end of the lake the boundary-line is located 3 miles easterly from the
river, following its turns, and the same distance from the lake shore,
all by an agreement recently reached between the two governments. The
summit level of the canal would therefore be the surface of the water
in Lake Nicaragua, which is carried down to Conchuda, 52 miles from
the lake on the San Juan River toward the east, by a great dam located
there, and to a lock between 4 and 5 miles from the lake toward the
west. Hence the summit level would stretch throughout a distance of
about 126 miles, leaving a little more than 46 miles on the Caribbean
end and about 12 miles on the Pacific end of the regular canal section.
The 50-mile stretch from the lake to the point where the canal cuts the
San Juan River near Conchuda is a canalized portion of the San Juan
River, as a large amount of excavation must be done there in order to
give the minimum required depth of 35 feet. The points of river bends
or curves are in some cases cut off by excavated canal section in order
to shorten the line and reduce the curvature. Considerable portions
of the line in the lake, particularly near Fort San Carlos, would be
excavated. For several miles in the latter vicinity large quantities of
silt and mud must be removed, as the lake is shallow and the bottom is
very soft. The entrance into the western portion of the canal at Las
Lajas requires a large amount of rock excavation, as the shore and bed
of the lake there are almost entirely of rock.
[Illustration: Scene on the San Juan River.]