Alaska 0
Arizona 0
Arkansas 787
California 1,854
Colorado 950
Connecticut 925
Dakota 290
Delaware 285
Florida 484
Georgia 2,308
Idaho 0
Illinois 6,980
Indiana 4,072
Indian Territory 281
Iowa 3,937
Kansas 3,226
Kentucky 1,464
Louisiana 539
Maine 987
Maryland 1,092
Massachusetts 1,825
Michigan 3,437
Minnesota 2,024
Mississippi 1,028
Missouri 3,016
Montana 0
Nebraska 1,181
Nevada 714
New Hampshire 942
New Jersey 1,594
New Mexico 0
New York 5,520
North Carolina 1,371
Ohio 4,680
Oregon 251
Pennsylvania 5,896
Rhode Island 182
South Carolina 1,352
Tennessee 1,638
Texas 2,072
Utah 486
Vermont 810
Virginia 1,648
Washington 110
West Virginia 576
Wisconsin 2,575
Wyoming 459
------
Total 76,640
In 1873 came the great financial crisis, with its terrible results of
interrupted production, poverty, and starvation, and an almost total
cessation of the work of building new railroads. The largest number of
miles ever built in any one year were constructed in 1872. The
greatest mileage is in Illinois, reaching 6,589; the smallest in Rhode
Island, 136, and in Washington Territory, 110. The State of
Massachusetts has one mile of railroad to 4.86 miles of territory,
this ratio being the greatest in the country. The longest road in
operation is the Chicago & Northwestern, extending 1,500 miles; the
shortest, the Little Saw-Mill Run Road in Pennsylvania, which is but
three miles in length. The total capital of railways in the country is
$6,000,000,000, or an average of $100,000 per mile. The earnings for
the year 1872 amounted to $454,969,000, or $7,500 per mile. The
largest net earnings recorded as made on any road were gained by the
New York Central & Hudson River, $8,260,827; the smallest on several
roads which not only earned nothing, but incurred a loss.
The catastrophe of 1873-'74 revealed the fact that the latter
condition of railroad finances was vastly more common than had been
suspected; and it is still doubtful whether the existing immense
network of railroads which covers the United States can be made, as a
whole, to pay even a moderate return on the money invested in their
construction. At the period of maximum rate of extension of railroads
in the United States--1873--the reported lengths of the railroads of
Europe and America were as follows:[94]
[94] _Railroad Gazette._
RAILROADS IN EUROPE AND AMERICA IN 1873.
----------------------------+------------+-------------+------------
COUNTRIES. | Railroads, | Population. | Area,
| Miles. | | Sq. Miles.
----------------------------+------------+-------------+------------
United States | 71,565 | 40,232,000 | 2,492,316
Germany | 12,207 | 40,111,265 | 212,091
Austria | 5,865 | 35,943,592 | 227,234
France | 10,333 | 36,469,875 | 201,900
Russia in Europe | 7,044 | 71,207,794 | 1,992,574
Great Britain, 1872 | 15,814 | 31,817,108 | 120,769
Belgium | 1,301 | 4,839,094 | 11,412
Netherlands | 886 | 3,858,055 | 13,464
Switzerland | 820 | 2,669,095 | 15,233
Italy | 3,667 | 26,273,776 | 107,961
Denmark | 420 | 1,784,741 | 14,453
Spain | 3,401 | 16,301,850 | 182,758
Portugal | 453 | 3,987,867 | 36,510
Sweden and Norway | 1,049 | 5,860,122 | 188,771
Greece | 100 | 1,332,508 | 19,941
----------------------------+------------+-------------+------------
The railroads in Great Britain comprise over 15,000 miles of track now
being worked in the United Kingdom, on which have been expended
$2,800,000,000. This sum is equal to five times the amount of the
annual value of all the real property in Great Britain, and two-thirds
of the national debt. After deducting all the working expenses, the
gross net annual revenue of all the roads exceeds by $110,000,000 the
total revenue from all sources of Belgium, Holland, Portugal, Denmark,
Sweden and Norway. An army of 100,000 officers and servants is in the
employ of the companies, and the value of the rolling-stock exceeds
$150,000,000.
SECTION III.--MARINE ENGINES.
The changes which have now become completed in the marine steam-engine
have been effected at a later date than those which produced the
modern locomotive. On the American rivers the modification of the
beam-engine since the time of Robert L. Stevens has been very slight.
The same general arrangement is retained, and the details are little,
if at all, altered. The pressure of steam is sometimes as high as 60
pounds per square inch.
[Illustration: FIG. 130.--Beam-Engine.]
The valves are of the disk or poppet variety, rising and falling
vertically. They are four in number, two steam and two exhaust valves
being placed at each end of the steam-cylinder. The beam-engine is a
peculiarly American type, seldom if ever seen abroad. Fig. 130 is an
outline sketch of this engine as built for a steamer plying on the
Hudson River. This class of engine is usually adopted in vessels of
great length, light draught, and high speed. But one steam-cylinder is
commonly used. The cross-head is coupled to one end of the beam by
means of a pair of links, and the motion of the opposite end of the
beam is transmitted to the crank by a connecting-rod of moderate
length. The beam has a cast-iron centre surrounded by a wrought-iron
strap of lozenge shape, in which are forged the bosses for the
end-centres, or for the pins to which the connecting-rod and the links
are attached. The main centre of the beam is supported by a
"gallows-frame" of timbers so arranged as to receive all stresses
longitudinally. The crank and shaft are of wrought-iron. The
valve-gear is usually of the form already mentioned as the Stevens
valve-gear, the invention of Robert L. and Francis B. Stevens. The
condenser is placed immediately beneath the steam-cylinder. The
air-pump is placed close beside it, and worked by a rod attached to
the beam. Steam-vessels on the Hudson River have been driven by such
engines at the rate of 20 miles an hour. This form of engine is
remarkable for its smoothness of operation, its economy and
durability, its compactness, and the latitude which it permits in the
change of shape of the long, flexible vessels in which it is generally
used, without injury by "getting out of line."
[Illustration: FIG. 131.--Oscillating Engine and Feathering
Paddle-Wheel.]
For paddle-engines of large vessels, the favorite type, which has been
the side-lever engine, is now rarely built. For smaller vessels, the
oscillating engine with feathering paddle-wheels is still largely
employed in Europe. This style of engine is shown in Fig. 131. It is
very compact, light, and moderately economical, and excels in
simplicity. The usual arrangement is such that the feathering-wheel
has the same action upon the water as a radial wheel of double
diameter. This reduction of the diameter of the wheel, while retaining
maximum effectiveness, permits a high speed of engine, and therefore
less weight, volume, and cost. The smaller wheel-boxes, by offering
less resistance to the wind, retard the progress of the vessel less
than those of radial wheels. Inclined engines are sometimes used for
driving paddle-wheels. In these the steam-cylinder lies in an inclined
position, and its connecting-rod directly connects the crank with the
cross-head. The condenser and air-pump usually lie beneath the
cross-head guides, and are worked by a bell-crank driven by links on
each side the connecting-rod, attached to the cross-head. Such engines
are used to some extent in Europe, and they have been adopted in the
United States navy for side-wheel gunboats. They are also used on the
ferry-boats plying between New York and Brooklyn.
[Illustration: FIG. 132.--The Two Rhode Islands, 1836-1876.]
Among the finest illustrations of recent practice in the construction
of side-wheel steamers are those built for the several routes between
New York and the cities of New England which traverse Long Island
Sound. Our illustration exhibits the form of these vessels, and also
shows well the modifications in structure and size which have been
made during this generation. The later vessel is 325 feet long, 45
feet beam, 80 feet wide over the "guards," and 16 feet deep, drawing
10 feet of water. The "frames" upon which the planking of the hull is
fastened are of white-oak, and the lighter and "top" timbers of cedar
and locust. The engine has a steam-cylinder 90 inches in diameter and
12 feet stroke of piston.[95] On each side the great saloons which
extend from end to end of the upper deck are state-rooms, containing
each two berths and elegantly furnished. The engine of this vessel is
capable of developing about 2,500 horse-power. The great wheels, of
which the paddle-boxes are seen rising nearly to the height of the
hurricane-deck, are 37-1/2 feet in diameter and 12 in breadth. The
hull of this vessel, including all wood-work, weighs over 1,200 tons.
The weight of the machinery is about 625 tons. The steamer makes 16
knots an hour when the engine is at its best speed--about 17
revolutions per minute--and its average speed is about 14 knots on
its route of 160 miles. The coal required to supply the furnaces of
such a vessel and with such machinery would be about 3 tons per hour.
or a little over 2-1/2 pounds per horse-power. The construction of
such a vessel occupies, usually, about a year, and costs a quarter of
a million dollars.
[95] The steam-cylinders of the engines of steamers Bristol and
Providence are 110 inches in diameter and of 12 feet stroke.
[Illustration: FIG. 133.--A Mississippi Steamboat.]
The non-condensing direct-acting engine is used principally on the
Western rivers, driven by steam of from 100 to 150 pounds pressure,
and exhausts its steam into the atmosphere. It is the simplest
possible form of direct-acting engine. The valves are usually of the
"poppet" variety, and are operated by cams which act at the ends of
long levers having their fulcra on the opposite side of the valve, the
stem of which latter is attached at an intermediate point. The engine
is horizontal, and the connecting-rod directly attached to cross-head
and crank-pin without intermediate mechanism. The paddle-wheel is
used, sometimes as a stern-wheel, as in the plan of Jonathan Hulls of
one and a half century ago, sometimes as a side-wheel, as is most
usual elsewhere. One of the most noted of these steamers, plying on
the Mississippi, is shown in the preceding sketch.
One of the largest of these steamers was the Grand Republic,[96] a
vessel 340 feet long, 56 feet beam, and 10-1/4 feet depth. The draught
of water of this great craft was 3-1/2 feet forward and 4-1/2 aft. The
two sets of compound engines, 28 and 56 inches diameter and of 10 feet
stroke, drive wheels 38-1/2 feet in diameter and 18 feet wide. The
boilers were steel. A steamer built still later on the Ohio has the
following dimensions: Length, 225 feet; breadth, 35-1/2 feet; depth, 5
feet; cylinders, 17-3/8 inches in diameter, 6 feet stroke; three
boilers. The hull and cabin were built at Jeffersonville, Ind. She has
40 large state-rooms. The cost of the steamer was $40,000.
[96] Burned in 1877.
These vessels have now opened to commerce the whole extent of the
great Mississippi basin, transporting a large share of the products of
a section of country measuring a million and a half square miles--an
area equal to many times that of New York State, and twelve times that
of the island of Great Britain--an area exceeding that of the whole of
Europe, exclusive of Russia and Turkey, and capable, if as thoroughly
cultivated as the Netherlands, of supporting a population of between
three and four hundred millions of people.
The steam-engine and propelling apparatus of the modern ocean-steamer
have now become almost exclusively the compound or double-cylinder
engine, driving the screw. The form and the location of the machinery
in the vessel vary with the size and character of the ship which it
drives. Very small boats are fitted with machinery of quite a
different kind from that built for large steamers, and war-vessels
have usually been supplied with engines of a design radically
different from that adopted for merchant-steamers.
[Illustration: FIG. 134.--Steam-Launch, New York Steam-Power Company.]
The introduction of _Steam-Launches_ and small pleasure-boats driven
by steam-power is of comparatively recent date, but their use is
rapidly increasing. Those first built were heavy, slow, and
complicated; but, profiting by experience, light and graceful boats
are now built, of remarkable swiftness, and having such improved and
simplified machinery that they require little fuel and can be easily
managed. Such boats have strong, carefully-modeled hulls, light and
strong boilers, capable of making a large amount of dry steam with
little fuel, and a light, quick-running engine, working without shake
or jar, and using steam economically.
[Illustration: FIG. 135.--Launch-Engine.]
The above sketch represents the engine built by a New York firm for
such little craft. This is the smallest size made for the market. It
has a steam-cylinder 3 inches in diameter and a stroke of piston of 5
inches, driving a screw 26 inches in diameter and of 3 feet pitch. The
maximum power of the engine is four or five times the nominal power.
The boiler is of the form shown in the illustrations of semi-portable
engines, and has a heating-surface, in this case, of 75 square feet.
The boat itself is like that seen on page 386, and is 25 feet long, of
5 feet 8 inches beam, and draws 2-1/4 feet of water. These little
machines weigh about 150 pounds per nominal horse-power, and the
boilers about 300.
Some of these little vessels have attained wonderful speed. A British
steam-yacht, the Miranda, 45-1/2 feet in length, 5-3/4 feet wide, and
drawing 2-1/2 feet of water, with a total weight of 3-3/4 tons, has
steamed nearly 18-1/2 miles an hour for short runs. The boat was
driven by an engine of 6 inches diameter of cylinder and 8 inches
stroke of piston, making 600 revolutions per minute, driving a
two-bladed screw 2-1/2 feet in diameter and of 3-1/3 feet pitch. Its
machinery had a total weight of two tons. Another English yacht, the
Firefly, is said to have made 18.94 miles an hour. A little French
yacht, the Hirondelle, has attained a speed of 16 knots, equal to
about 18-1/2 miles, an hour. This was, however, a much larger vessel
than the preceding. One of the most remarkable of these little
steamers is a torpedo-boat built for the United States navy. This
vessel is 60 feet long, 6 feet wide, and 5 feet deep; its screw is 38
inches in diameter and of 5 feet pitch, two-bladed, and is driven, by
a very light engine and boiler, 400 revolutions per minute, the boat
attaining a speed of 19 to 20 miles an hour. Another little vessel,
the Vision, made nearly as great speed, developing 20 horse-power with
engine and boiler weighing but about 400 pounds.
Yachts of high speed require such weight and bulk of engine that but
little space is left for cabins, and they are usually exceedingly
uncomfortable vessels. In the Miranda the weight of machinery is more
than one-half the total weight of the whole. An illustration of the
more comfortable and more generally liked pleasure-yacht is the Day
Dream. The length is 105 feet, and the boat draws 5-1/2 feet of
water. There are two engines, having steam-cylinders 14 inches in
diameter and of the same length of stroke, direct-acting, condensing,
and driving a screw, of 7 feet diameter and of 10-1/2 feet pitch, 135
revolutions a minute, giving the yacht a speed of 13-1/2 knots an
hour.
[Illustration: FIG. 136.--Horizontal, Direct-acting Naval
Screw-Engine.]
In larger vessels, as in yachts, in nearly all cases, the ordinary
screw-engine is direct-acting. Two engines are placed side by side,
with cranks on the shaft at an angle of 90 deg. with each other. In
merchant-steamers the steam-cylinders are usually vertical and
directly over the crank-pins, to which the cross-heads are coupled.
The condenser is placed behind the engine-frame, or, where a
jet-condenser is used, the frame itself is sometimes made hollow, and
serves as a condenser. The air-pump is worked by a beam connected by
links with the cross-head. The general arrangement is like that shown
in Figs. 137 and 138. For naval purposes such a form is objectionable,
since its height is so great that it would be exposed to injury by
shot. In naval engineering the cylinder is placed horizontally, as in
Fig. 136, which is a sectional view, representing an horizontal,
direct-acting naval screw-engine, with jet-condenser and double-acting
air and circulating pumps. _A_ is the steam-cylinder, _B_ the piston,
which is connected to the crank-pin by the piston-rod, _D_, and
connecting-rod, _E_. _F_ is the cross-head guide. The eccentrics,
_G_, operate the valve, which is of the "three-ported variety," by a
Stephenson link. Reversing is effected by the hand-wheel, _C_, which,
by means of a gear, _m_, and a rack, _k_, elevates and depresses the
link, and thus reverses the valve.
[Illustration: FIG. 137.--Compound Marine Engine. Side Elevation.]
The trunk-engine, in which the connecting-rod is attached directly to
the piston and vibrates within a trunk or cylinder secured to the
piston, moving with it, and extending outside the cylinder, like an
immense hollow piston-rod, is frequently used in the British navy. It
has rarely been adopted in the United States.
[Illustration: FIG. 138.--Compound Marine Engine. Front Elevation and
Section.]
In nearly all steam-vessels which have been built for the merchant
service recently, and in some naval vessels, the compound engine has
been adopted. Figs. 137 and 138 represent the usual form of this
engine. Here _A A_, _B B_ are the small and the large, or the
high-pressure and the low-pressure cylinders respectively. _C C_ are
the valve-chests. _G G_ is the condenser, which is invariably a
surface-condenser. The condensing water is sometimes directed around
the tubes contained within the casing, _G G_, while the steam is
exhausted around them and among them, and sometimes the steam is
condensed within the tubes, while the injection-water which is sent
into the condenser to produce condensation passes around the exterior
of the tubes. In either case, the tubes are usually of small diameter,
varying from five-eighths to half an inch, and in length from four to
seven feet. The extent of heating-surface is usually from one-half to
three-fourths that of the heating-surface of the boilers.
The air and circulating pumps are placed on the lower part of the
condenser-casting, and are operated by a crank on the main shaft at
_N_; or they are sometimes placed as in the style of engine last
described, and driven by a beam worked by the cross-head. The
piston-rods, _T S_, are guided by the cross-heads, _V V_, working in
slipper-guides, and to these cross-heads are attached the
connecting-rods, _X X_, driving the cranks, _M M_. The cranks are now
usually set at right angles; in some engines this angle is increased
to 120 deg., or even 180 deg.. Where it is arranged as here shown, an
intermediate reservoir, _P O_, is placed between the two cylinders to
prevent the excessive variations of pressure that would otherwise
accompany the varying relative motions of the pistons, as the steam
passes from the high-pressure to the low-pressure cylinder. Steam from
the boilers enters the high-pressure steam-chest, _X_, and is admitted
by the steam-valve alternately above and below the piston as usual.
The exhaust steam is conducted through the exhaust passage around into
the reservoir, _P_, whence it it is taken by the low-pressure
cylinder, precisely as the smaller cylinder drew its steam from the
boiler. From the large or low-pressure cylinder the steam is exhausted
into the condenser. The valve-gear is usually a Stephenson link, _g
e_, the position of which is determined, and the reversal of which is
accomplished, by a hand-wheel, _o_, and screw, _m n p_, which, by the
bell-crank, _k i_, are attached to the link, _g e_. The "box-framing"
forms also the hot-well. The surface-condenser is cleared by a
single-acting air-pump, inside the frame, at _T_. The feed-pump and
the bilge-pumps are driven from the cross-head of the air-pump.
[Illustration: John Elder.]
The successful introduction of the double-cylinder engine was finally
accomplished by the exertions of a few engineers, who were at once
intelligent enough to understand its advantages, and energetic and
enterprising enough to push it forward in spite of active opposition,
and powerful enough, pecuniarily and in influence, to succeed. The
most active and earnest of these eminent men was John Elder, of the
firm of Randolph, Elder & Co., subsequently John Elder & Co., of
Glasgow.[97]
[97] _Vide_ "Memoir of John Elder," W. J. M. Rankine, Glasgow, 1871.
Elder was of Scotch descent. His ancestors had, for generations,
shown great skill and talent in construction, and had always been
known as successful millwrights. John Elder was born at Glasgow, March
8, 1824, and died in London, September 17, 1869. He was educated at
the Glasgow High-School and in the College of Engineering at the
University of Glasgow, where, however, his attendance was but for a
short time. He learned the trade under his father in the workshops of
the Messrs. Napier, and became an unusually expert draughtsman. After
spending three years in charge of the drawing-office at the
engine-building works of Robert Napier, where his father had been
manager, Elder became a partner in the firm which had previously been
known as Randolph, Elliott & Co., in the year 1852. The firm commenced
building iron vessels in 1860.
In the mean time, the experiments of Hornblower and Wolff, of Allaire
and Smith, and of McNaught, Craddock, and Nicholson, together with the
theoretical investigations of Thompson, Rankine, Clausius, and others,
had shown plainly in what direction to look for improvement upon then
standard engines, and what direction practice was taking with all
types. The practical deductions which were becoming evident were
recognized very early by Elder, and he promptly began to put in
practice the principles which his knowledge of thermo-dynamics and of
mechanics enabled him to appreciate. He adopted the compound engine,
and coupled his cranks at angles of 180 deg., in order to avoid losses due
to the friction of the crank-shaft in its bearings, by effecting a
partial counterbalancing of pressures on the journals. Elder was one
of the first to point out the fact that the compound engine had proved
itself more efficient than the single-cylinder engine, only when the
pressure of steam carried and the extent to which expansion was
adopted exceeded the customary practice of his time. His own practice
was, from the first, successful, and from 1853 to 1867 he and his
partners were continually engaged in the construction of steamers and
fitting them with compound engines.
The engines of their first vessel, the Brandon, required but 3-1/4
pounds of coal per hour and per horse-power, in 1854, when the usual
consumption was a third more. Five years later, they had built engines
which consumed a third less than those of the Brandon; and
thenceforward, for many years, their engines, when of large size,
exhibited what was then thought remarkable economy, running on a
consumption of from 2-1/4 to 2-1/2 pounds.
In the year 1865 the British Government ordered a competitive trial of
three naval vessels, which only differed in the form of their engines.
The Arethusa was fitted with trunk-engines of the ordinary kind; the
Octavia had three steam-cylinders, coupled to three cranks placed at
angles of 120 deg. with each other; and the Constance was fitted with
compound engines, two sets of three cylinders each, and each taking
steam from the boiler into one cylinder, passing it through the other
two with continuous expansion, and finally exhausting from the third
into the condenser. These vessels, during one week's steaming at sea,
averaged, respectively, 3.64, 3.17, and 2.51 pounds of coal per hour
and per horse-power, and the Constance showed a marked superiority in
the efficiency of the mechanism of her engines, when the losses by
friction were compared.
The change from the side-lever single-cylinder engine, with
jet-condenser and paddle-wheels, to the direct-acting compound engine,
with surface-condenser and screw-propellers, has occurred within the
memory and under the observation of even young engineers, and it may
be considered that the revolution has not been completely effected.
This change in the design of engine is not as great as it at first
seemed likely to become. Builders have but slowly learned the
principles stated above in reference to expansion in one or more
cylinders, and the earlier engines were made with a high and low
pressure cylinder working on the same connecting-rod, and each machine
consisted of four steam-cylinders. It was at last discovered that a
high-pressure single-cylinder engine exhausting into a separate
larger low-pressure engine might give good results, and the compound
engine became as simple as the type of engine which it displaced. This
independence of high and low pressure engines is not in itself novel,
for the plan of using the exhaust of a high-pressure engine to drive a
low-pressure condensing engine was one of the earliest of known
combinations.
The advantage of introducing double engines at sea is considerably
greater than on land. The coal carried by a steam-vessel is not only
an item of great importance in consequence of its first cost, but,
displacing its weight or bulk of freight which might otherwise be
carried, it represents so much non-paying cargo, and is to be charged
with the full cost of transportation in addition to first cost. The
best of steam-coal is therefore usually chosen for steamers making
long voyages, and the necessity of obtaining the most economical
engines is at once seen, and is fully appreciated by steamship
proprietors. Again, an economy of one-fourth of a pound per
horse-power per hour gives, on a large transatlantic steamer, a saving
of about 100 tons of coal for a single voyage. To this saving of cost
is to be added the gain in wages and sustenance of the labor required
to handle that coal, and the gain by 100 tons of freight carried in
place of the coal.
For many years the change which has here been outlined, in the forms
of engine and the working of steam expansively, was retarded by the
inefficiency of methods and tools used in construction. With gradual
improvement in tools and in methods of doing work, it became possible
to control higher steam and to work it successfully; and the change in
this direction has been steadily going on up to the present time with
all types of steam-engine. At sea this rise of pressure was for a
considerable time retarded by the serious difficulty encountered in
the tendency of the sulphate of lime to deposit in the boiler. When
steam-pressure had risen to 25 pounds per square inch, it was found
that no amount of "blowing out" would prevent the deposition of
seriously large quantities of this salt, while at the lower pressures
at first carried at sea no troublesome precipitation occurred, and the
only precaution necessary was to blow out sufficient brine to prevent
the precipitation of common salt from a supersaturated solution. The
introduction of surface-condensation was promptly attempted as the
remedy for this evil, but for many years it was extremely doubtful
whether its disadvantages were not greater than its advantages. It was
found very difficult to keep the condensers tight, and boilers were
injured by some singular process of corrosion, evidently due to the
presence of the surface-condenser. The simple expedient of permitting
a very thin scale to form in the boiler was, after a time, hit upon as
a means of overcoming this difficulty, and thenceforward the greatest
obstacle to the general introduction was the conservative disposition
found among those who had charge of marine machinery, which
conservatism regarded with suspicion every innovation. Another trouble
arose from the difficulty of finding men neither too indolent nor too
ignorant to take charge of the new condenser, which, more complicated
and more readily disarranged than the old, demanded a higher class of
attendants. Once introduced, however, the surface-condenser removed
the obstacle to further elevation of steam-pressure, and the rise from
20 to 60 pounds pressure soon occurred. Elder and his competitors on
the Clyde were the first to take advantage of the fact when these
higher pressures became practicable.
The lightness of engine and the smaller weight of boiler secured when
the simpler type of "compound" engine is used are great advantages,
and, when coupled with the fact that by no other satisfactory device
can great expansion and consequent economy of fuel be obtained at sea,
the advantages are such as to make the adoption of this style of
engine imperative for ship-propulsion.
This extreme lightness in machinery has been largely, also, the result
of very careful and skillful designing, of intelligent construction,
and of care in the selection and use of material. British builders
had, until after the introduction of these later types of
vessels-of-war, been distinguished rather by the weight of their
machinery than for nice calculation and proportioning of parts. Now
the engines of the heavy iron-clads are models of good proportions,
excellence in materials, and of workmanship, which are well worthy of
study. The weight per indicated horse-power has been reduced from 400
or 500 pounds to less than half that amount within the last ten years.
This has been accomplished by forcing the boilers--although thus, to
some extent, losing economy--by higher steam-pressure, a very much
higher piston-speed, reduction of friction of parts, reduction of
capacity for coal-stowage, and exceedingly careful proportioning.
The reduction of coal-bunker capacity is largely compensated by
the increase of economy secured by superheating, by increased
expansion, elevation of piston-speed, and the introduction of
surface-condensation.
A good marine steam-engine of the form which was considered standard
15 or 20 years ago, having low-pressure boilers carrying steam at 20
or 25 pounds pressure as a maximum, expanding twice or three times,
and having a jet-condenser, would require about 30 or 35 pounds of
feed-water per horse-power per hour; substituting surface-condensation
for that produced by the jet brought down the weight of steam used to
from 25 to 30 pounds; increasing steam-pressure to 60 pounds,
expanding from five to eight times, and combining the special
advantages of the superheater and the compound engine with
surface-condensation, has reduced the consumption of steam to 20, or
even, in some cases, 15 pounds of steam per horse-power per hour.
Messrs. Perkins, of London, guarantee, as has already been stated, to
furnish engines capable of giving a horse-power with a consumption of
but 1-1/4 pound of coal. Mr. C. E. Emery reports the United States
revenue-steamer Hassler, designed by him, to have given an ordinary
sea-going performance which is probably fully equal to anything yet
accomplished. The Hassler is a small steamer, of but 151 feet in
length, 24-1/2 feet beam, and 10 feet draught. The engines have
steam-cylinders 18.1 and 28 inches diameter, respectively, and of 28
inches stroke of piston, indicating 125 horse-power; with steam at 75
pounds pressure, and at a speed of but 7 knots, the coal consumed was
but 1.87 pound per horse-power per hour.
The committee of the British Admiralty on designs of ships-of-war have
reported recently: "The carrying-power of ships may certainly be to
some extent increased by the adoption of compound engines in her
Majesty's service. Its use has recently become very general in the
mercantile marine, and the weight of evidence in favor of the large
economy of fuel thereby gained is, to our minds, overwhelming and
conclusive. We therefore beg earnestly to recommend that the use of
compound engines may be generally adopted in ships-of-war hereafter to
be constructed, and applied, whenever it can be done with due regard
to economy and to the convenience of the service, to those already
built."
The forms of screws now employed are exceedingly diverse, but those in
common use are not numerous. In naval vessels it is common to apply
screws of two blades, that they may be hoisted above water into a
"well" when the vessel is under sail, or set with the two blades
directly behind the stern-post, when their resistance to the forward
motion of the vessel will be comparatively small. In other vessels,
and in the greater number of full-power naval vessels, screws of three
or four blades are used.
The usual form of screw (Fig. 139) has blades of nearly equal breadth
from the hub to the periphery, or slightly widening toward their
extremities, as is seen in an exaggerated degree in Fig. 140,
representing the form adopted for tug-boats, where large surface near
the extremity is more generally used than in vessels of high speed
running free. In the Griffith screw, which has been much used, the hub
is globular and very large. The blades are secured to the hub by
flanges, and are bolted on in such a manner that their position may be
changed slightly if desired. The blades are shaped like the section of
a pear, the wider part being nearest the hub, and the blades tapering
rapidly toward their extremities. A usual form is intermediate between
the last, and is like that shown in Fig. 141, the hub being
sufficiently enlarged to permit the blades to be attached as in the
Griffith screw, but more nearly cylindrical, and the blades having
nearly uniform width from end to end.
[Illustration: FIG. 139.--Screw-Propeller.]
[Illustration: FIG. 140.--Tug-boat Screw.]
[Illustration: FIG. 141.--Hirsch Screw.]
The pitch of a screw is the distance which would be traversed by the
screw in one revolution were it to move through the water without
slip; i. e., it is double the distance _C D_, Fig. 140. _C D'_
represents the helical path of the extremity of the blade _B_, and _O
E F H K_ is that of the blade _A_. The proportion of diameter to the
pitch of the screw is determined by the speed of the vessel. For low
speed the pitch may be as small as 1-1/4 the diameter. For vessels of
high speed the pitch is frequently double the diameter. The diameter
of the screw is made as great as possible, since the slip decreases
with the increase of the area of screw-disk. Its length is usually
about one-sixth of the diameter. A greater length produces loss by
increase of surface causing too great friction, while a shorter screw
does not fully utilize the resisting power of the cylinder of water
within which it works, and increased slip causes waste of power. An
empirical value for the probable slip in vessels of good shape, which
is closely approximate usually, is _S_ = 4(_M_/_A_), in which _S_ is
the slip per cent., and _M_ and _A_ are the areas of the midship
section and of the screw-disk in square feet.
The most effective screws have slightly greater pitch at the periphery
than at the hub, and an increasing pitch from the forward to the rear
part of the screw. The latter method of increasing pitch is more
generally adopted alone. The thrust of the screw is the pressure which
it exerts in driving the vessel forward. In well-formed vessels, with
good screws, about two-thirds of the power applied to the screw is
utilized in propulsion, the remainder being wasted in slip and other
useless work. Its efficiency is in such a case, therefore, 66 per
cent. Twin screws, one on each side of the stern-post, are sometimes
used in vessels of light draught and considerable breadth, whereby
decreased slip is secured.
As has already been stated, the introduction of the compound engine
has been attempted, but with less success than in Europe, by several
American engineers.
The most radical change in the methods of ship-propulsion which has
been successfully introduced in some localities has been the adoption
of a system of "wire-rope towage." It is only well adapted for cases
in which the steamer traverses the same line constantly, moving
backward and forward between certain points, and is never compelled to
deviate to any considerable extent from the path selected. A similar
system is in use in Canada, but it has not yet come into use in the
United States, notwithstanding the fact that, wherever its adoption is
practicable, it has a marked superiority in economy over the usual
methods of propulsion. With chain or rope traction there is no loss by
slip or oblique action, as in both screw and paddle-wheel propulsion.
In the latter methods these losses amount to an important fraction of
the total power; they rarely, if ever, fall below a total of 25 per
cent., and probably in towage exceed 50 per cent. The objection to the
adoption of chain-propulsion, as it is also often called, is the
necessity of following closely the line along which the chain or the
rope is laid. There is, however, much less difficulty than would be
anticipated in following a sinuous route or in avoiding obstacles in
the channel or passing other vessels. The system is particularly well
adapted for use on canals.
The steam-boilers in use in the later and best marine engineering
practice are of various forms, but the standard types are few in
number. That used on river-steamers in the United States has already
been described.
[Illustration: FIG. 142.--Marine Fire-tubular Boiler. Section.]
Fig. 142 is a type of marine tubular boiler which is in most extensive
use in sea-going steamers for moderate pressure, and particularly for
naval vessels. Here the gases pass directly into the back connection
from the fire, and thence forward again, through horizontal tubes, to
the front connection and up the chimney. In naval vessels the
steam-chimney is omitted, as it is there necessary to keep all parts
of the boiler as far below the water-line as possible. Steam is taken
from the boiler by pipes which are carried from end to end of the
steam-space, near the top of the boiler, the steam entering these
pipes through small holes drilled on the other side. Steam is thus
taken from the boiler "wet," but no large quantity of water can
usually be "entrained" by the steam.
A marine boiler has been quite extensively introduced into the United
States navy, in which the gases are led from the back connection
through a tube-box around and among a set of upright water-tubes,
which are filled with water, circulation taking place freely from the
water-space immediately above the crown-sheet of the furnace up
through these tubes into the water-space above them. These
"water-tubular" boilers have a slight advantage over the
"fire-tubular" boilers already described in compactness, in steaming
capacity, and in economical efficiency. They have a very marked
advantage in the facility with which the tubes may be scraped or freed
from the deposit when a scale of sulphate of lime or other salt has
formed within them by precipitation from the water. The fire-tubular
boiler excels in convenience of access for plugging up leaking tubes,
and is much less costly than the water-tubular. The water-tube class
of boilers still remain in extensive use in the United States naval
steamers. They have never been much used in the merchant service,
although introduced by James Montgomery in the United States and by
Lord Dundonald in Great Britain twenty years earlier. Opinion still
remains divided among engineers in regard to their relative value.
They are gradually reassuming prominence by their introduction in the
modified form of sectional boilers.
[Illustration: FIG. 143.--Marine High-Pressure Boiler. Section.]
Marine boilers are now usually given the form shown in section in Fig.
143. This form of boiler is adopted where steam-pressures of 60
pounds and upward are carried, as in steam-vessels supplied with
compound engines, cylindrical forms being considered the best with
high pressures. The large cylindrical flues, therefore, form the
furnaces as shown in the transverse sectional view. The gases rise, as
shown in the longitudinal section, through the connection, and pass
back to the end of the boiler through the tubes, and thence, instead
of entering a steam-chimney, they are conducted by a smoke-connection,
not shown in the sketch, to the smoke funnel or stack. In
merchant-steamers, a steam-drum is often mounted horizontally above
the boiler. In other cases a separator is attached to the steam-pipe
between boilers and engines. This usually consists of an iron tank,
divided by a vertical partition extending from the top nearly to the
bottom. The steam, entering the top at one side of this partition,
passes underneath it, and up to the top on the opposite side, where it
issues into a steam-pipe leading directly to the engine. The sudden
reversal of its course at the bottom causes it to leave the suspended
water in the bottom of the separator, whence it is drained off by
pipes.
The most interesting illustrations of recent practice in marine
engineering and naval architecture are found in the steamers which are
now seen on transoceanic routes for the merchant service, and, in the
naval service, in the enormous iron-clads which have been built in
Great Britain.
The City of Peking is one of the finest examples of American practice.
This vessel was constructed for the Pacific Mail Company. The hull is
423 feet long, of 48 feet beam, and 38-1/2 feet deep. Accommodations
are furnished for 150 cabin and 1,800 steerage passengers, and the
coal-bunkers "stow" 1,500 tons of coal. The iron plates of which the
sides and bottom are made are from 11/16 to one inch in thickness. The
weight of iron used in construction was about 5,500,000 pounds. The
machinery weighed nearly 2,000,000 pounds, with spare gear and
accessory apparatus. The engines are compound, with two
steam-cylinders of 51 inches and two of 88 inches diameter, and a
stroke of piston of 4-1/2 feet. The condensing water is sent through
the surface-condensers by circulating-pumps driven by their own
engines. Ten boilers furnish steam to these engines, each having a
diameter of 13 feet, a length of 13-1/2 feet, and a thickness of
"shell" of 13/16 inch. Each has three furnaces, and contains 204
tubes of an outside diameter of 3-1/4 inches. All together, they
have 520 square feet of grate-surface and 17,000 square feet of
heating-surface. The area of cooling-surface in the condensers is
10,000 square feet. The City of Rome, a ship of later design, is 590
feet long, "over all," 52 feet beam, 52 feet deep, and measures 8,300
tons. The engines, of 8,500 horse-power, will drive the vessel 18
knots (21 miles) an hour; they have six steam-cylinders (three high
and three low pressure), and are supplied with steam by 8 boilers
heated by 48 furnaces. The hull is of steel, the bottom double, and
the whole divided into ten compartments by transverse bulkheads. Two
longitudinal bulkheads in the engine and boiler compartments add
greatly to the safety of the vessel.
The most successful steam-vessels in general use are these
screw-steamers of transoceanic lines. Those of the transatlantic lines
are now built from 350 to 550 feet long, generally propelled from 12
to 18 knots (14 to 21 miles) an hour, by engines of from 3,000 to
8,000 horse-power, consuming from 70 to 250 tons of coal a day, and
crossing the Atlantic in from eight to ten days. These vessels are now
invariably fitted with the compound engine and surface-condensers. One
of these vessels, the Germanic, has been reported at Sandy Hook, the
entrance to New York Harbor, in 7 days 11 hours 37 minutes from
Queenstown--a distance, as measured by the log and by observation, of
2,830 miles. Another steamer, the Britannic, has crossed the Atlantic
in 7 days 10 hours and 53 minutes. These vessels are of 5,000 tons
burden, of 750 "nominal" horse-power (probably 5,000 actual).
[Illustration: FIG. 144.--The Modern Steamship.]
The modern steamship is as wonderful an illustration of ingenuity and
skill in all interior arrangements as in size, power, and speed. The
size of sea-going steamers has become so great that it is unsafe to
intrust the raising of the anchor or the steering of the vessel to
manual power and skill; and these operations, as well as the loading
and unloading of the vessel, are now the work of the same great
motor--steam.
The now common form of auxiliary engine for controlling the helm is
one of the inventions of the American engineer F. E. Sickels, who
devised the "Sickels cut-off," and was first invented about 1850. It
was exhibited at London at the International Exhibition of 1851. It
consists[98] principally of two cylinders working at right angles upon
a shaft geared into a large wheel fastened by a friction-plate lined
with wood, and set by a screw to any desired pressure on the
steering-apparatus. The wheel turned by the steersman is connected
with the valve-gear of the cylinders, so that the steam, or other
motor, will move the rudder precisely as the helmsman moves the wheel
adjusting the steam-valves. This wheel thus becomes the
steering-wheel. The apparatus is usually so arranged that it may be
connected or disconnected in an instant, and hand-steering adopted if
the smoothness of the sea and the low speed of the vessel make it
desirable or convenient. This method was first adopted in the United
States on the steamship Augusta.
[98] "Official Catalogue," 1862, vol. iv., Class viii., p. 123.
The same inventor and others have contrived "steam-windlasses," some
of which are in general use on large vessels. The machinery of these
vessels is also often fitted with a steam "reversing-gear," by means
of which the engines are as easily man[oe]uvred as are those of the
smallest vessels, to which hand-gear is always fitted. In one of these
little auxiliary engines, as devised by the author, a small handle
being adjusted to a marked position, as to the point marked "stop" on
an index-plate, the auxiliary engine at once starts, throws the
valve-gear into the proper position--as, if a link-motion, into
"middle-gear"--thus stopping the large engines, and then it itself
stops. Setting the handle so that its pointer shall point to "ahead,"
the little engine starts again, sets the link in position to go ahead,
thus starting the large engines, and again stops itself. If set at
"back," the same series of operations occurs, leaving the main engines
backing and the little "reversing engine" stopped. A number of forms
of reversing engine are in use, each adapted to some one type of
engine.
The hull of the transatlantic steamer is now always of iron, and is
divided into a number of "compartments," each of which is water-tight
and separated from the adjacent compartments by iron "bulkheads," in
which are fitted doors which, when closed, are also water-tight. In
some cases these doors close automatically when the water rises in the
vessel, thus confining it to the leaking portion.
Thus we have already seen a change in transoceanic lines from steamers
like the Great Western (1837), 212 feet in length, of 35-1/2 feet
beam, and 23 feet depth, driven by engines of 450 horse-power, and
requiring 15 days to cross the Atlantic, to steamships over 550 feet
long, 55 feet beam, and 55 feet deep, with engines of 10,000
horse-power, crossing the Atlantic in 7 days; iron substituted for
wood in construction, the cost of fuel reduced one-half, and the speed
raised from 8 to 18 knots and over. In the earlier days of steamships
they were given a proportion of length to breadth of from 5 to 6 to 1;
in forty years the proportion increased until 11 to 1 was reached.
The whole naval establishment of every country has been greatly
modified by the recent changes in methods of attack and defense; but
the several classes of ships which still form the naval marine are all
as dependent upon their steam-machinery as ever.
[Illustration: H. B. M. Iron-Clad Captain. H. B. M. Iron-Clad
Thunderer. U. S. Iron-Clad Dictator. U. S. Iron-Clad Monitor. H. B. M.
Iron-Clad Giatton. French Iron-Clad Dunderberg. FIG. 145.--Modern
Iron-Clads.]
It is only recently that the attempt seems to have been made to
determine a classification of war-vessels and to plan a naval
establishment which shall be likely to meet fully the requirements of
the immediate future. It has hitherto been customary simply to make
each ship a little stronger, faster, or more powerful to resist or to
make attack than was the last. The fact that the direction of
progress in naval science and architecture is plainly perceivable, and
that upon its study may be based a fair estimate of the character and
relative distribution of several classes of vessels, seems to have
been appreciated by very few.
In the year 1870 the writer proposed[99] a classification of vessels
other than torpedo-vessels, which has since been also proposed in a
somewhat modified form by Mr. J. Scott Russell.[100] The author then
remarked that the increase so rapidly occurring in weight of ordnance
and of armor, and in speed of war-vessels, would probably soon compel
a division of the vessels of every navy into three classes of ships,
exclusive of torpedo-vessels, one for general service in time of
peace, the others for use only in time of war.
[99] _Journal Franklin Institute_, 1870. H. B. M. S. Monarch.
[100] London _Engineering_, 1875.
"The first class may consist of unarmored vessels of moderate size,
fair speed under steam, armed with a few tolerably heavy guns, and
carrying full sail-power.
"The second class may be vessels of great speed under steam,
unarmored, carrying light batteries and as great spread of canvas as
can readily be given them; very much such vessels as the Wampanoag
class of our own navy were intended to be--calculated expressly to
destroy the commerce of an enemy.
"The third class may consist of ships carrying the heaviest possible
armor and armament, with strongly-built bows, the most powerful
machinery that can be given them, of large coal-carrying capacity, and
unencumbered by sails, everything being made secondary to the one
object of obtaining victory in contending with the most powerful of
possible opponents. Such vessels could never go to sea singly, but
would cruise in couples or in squadrons. It seems hardly doubtful that
attempts to combine the qualities of all classes in a single vessel,
as has hitherto been done, will be necessarily given up, although the
classification indicated will certainly tend largely to restrict naval
operations."
The introduction of the stationary, the floating, and the automatic
classes of torpedoes, and of torpedo-vessels, has now become
accomplished, and this element, which it was predicted by Bushnell and
by Fulton three-quarters of a century ago would at some future time
become important in warfare, is now well recognized by all nations.
How far it may modify future naval establishments cannot be yet
confidently stated, but it seems sufficiently evident that the attack,
by any navy, of stationary defenses protected by torpedoes is now
quite a thing of the past. It may be perhaps looked upon as
exceedingly probable that torpedo-ships of very high speed will yet
drive all heavily-armored vessels from the ocean, thus completing the
historic parallel between the man-in-armor of the middle ages and the
armored man-of-war of our own time.[101]
[101] _Vide_ "Report on Machinery and Manufactures, etc., at
Vienna," by the author, Washington, 1875.
Of these classes, the third is of most interest, as exhibiting most
perfectly the importance and variety of the work which the
steam-engine is made to perform. On the later of these vessels, the
anchor is raised by a steam anchor-hoisting apparatus; the heavier
spars and sails are handled by the aid of a steam-windlass; the helm
is controlled by a steering-engine, and the helmsman, with his little
finger, sets in motion a steam-engine, which adjusts the rudder with a
power which is unimpeded by wind or sea, and with an exactness that
could not be exceeded by the hand-steering gear of a yacht; the guns
are loaded by steam, are elevated or depressed, and are given lateral
training, by the same power; the turrets in which the guns are incased
are turned, and the guns are whirled toward every point of the
compass, in less time than is required to sponge and reload them; and
the ship itself is driven through the water by the power of ten
thousand horses, at a speed which is only excelled on land by that of
the railroad-train.
The British Minotaur was one of the earlier iron-clads. The great
length and consequent difficulty of man[oe]uvring, the defect of
speed, and the weakness of armor of these vessels have led to the
substitution of far more effective designs in later constructions. The
Minotaur is a four-masted screw iron-clad, 400 feet long, of 59 feet
beam and 26-1/2 feet draught of water. Her speed at sea is about
12-1/2 knots, and her engines develop, as a maximum, nearly 6,000
indicated horse-power. Her heaviest armor-plates are but 6 inches in
thickness. Her extreme length and her unbalanced rudder make it
difficult to turn rapidly. With _eighteen men at the steering-wheel_
and sixty others on the tackle, the ship, on one occasion, was 7-1/2
minutes in turning completely around. These long iron-clads were
succeeded by the shorter vessels designed by Mr. E. J. Reed, of which
the first, the Bellerophon, was of 4,246 tons burden, 300 feet long by
56 feet beam, and 24-1/2 feet draught, of the 14-knot speed, with
4,600 horse-power; and having the "balanced rudder" used many years
earlier in the United States by Robert L. Stevens,[102] it can turn in
four minutes with eight men at the wheel. The cost of construction was
some $600,000 less than that of the Minotaur. A still later vessel,
the Monarch, was constructed on a system quite similar to that known
in the United States as the Monitor type, or as a turreted iron-clad.
This vessel is 330 feet long, 57-1/2 feet wide, and 36 feet deep,
drawing 24-1/2 feet of water. The total weight of ship and contents is
over 8,000 tons, and the engines are of over 8,500 horse-power. The
armor is 6 and 7 inches thick on the hull, and 8 inches on the two
turrets, over a heavy teak backing. The turrets contain each two
12-inch rifled guns, weighing 25 tons each, and, with a charge of 70
pounds of powder, throwing a shot of 600 pounds weight with a velocity
of 1,200 feet per second, and giving it a _vis viva_ equivalent to the
raising of over 6,100 tons one foot high, and equal to the work of
penetrating an iron plate 13-1/2 inches thick. This immense vessel is
driven by a pair of "single-cylinder" engines having steam-cylinders
_ten feet_ in diameter and of 4-1/2 feet stroke of piston, driving a
two-bladed Griffith screw of 23-1/2 feet diameter and 26-1/2 feet
pitch, 65 revolutions, at the maximum speed of 14.9 knots, or about
17-1/2 miles, an hour. To drive these powerful engines, boilers having
an aggregate of about 25,000 square feet (or more than a half-acre) of
heating-surface are required, with 900 square feet of grate-surface.
The refrigerating surface in the condensers has an area of 16,500
square feet--over one-third of an acre. The cost of these engines and
boilers was L66,500.
[102] Still in use on the Hoboken ferry-boats.
Were all this vast steam-power developed, giving the vessel a speed of
15 knots, the ship, if used as a "ram," would strike an enemy at rest
with the tremendous "energy" of 48,000 foot-tons--equal to the shock
of the projectiles of eight or nine such guns as are carried by the
iron-clad itself, simultaneously discharged upon one spot.
But even this great vessel is less formidable than later vessels. One
of the latter, the Inflexible, is a shorter but wider and deeper ship
than the Monarch, measuring 320 feet long, 75 feet beam, and 25
draught, displacing over 10,000 tons. The great rifles carried by this
vessel weigh 81 tons each, throwing shot weighing a half-ton from
behind iron-plating two feet in thickness. The steam-engines are of
about the same power as those of the Monarch, and give this enormous
hull a speed of 14 knots an hour.
The navy of the United States does not to-day possess iron-clads of
power even approximating that of either of several classes of British
and other foreign naval vessels.
The largest vessel of any class yet constructed is the Great Eastern
(Fig. 146), begun in 1854 and completed in 1859, by J. Scott Russell,
on the Thames, England. This ship is 680 feet long, 83 feet wide, 58
feet deep, 28 feet draught, and of 24,000 tons measurement. There are
four paddle and four screw engines, the former having steam-cylinders
74 inches in diameter, with 14 feet stroke, the latter 84 inches in
diameter and 4 feet stroke. They are collectively of 10,000 actual
horse-power. The paddle-wheels are 56 feet in diameter, the screw 24
feet. The steam-boilers supplying the paddle-engines have 44,000
square feet (more than an acre) of heating-surface. The boilers
supplying the screw-engines are still larger. At 30 feet draught, this
great vessel displaces 27,000 tons. The engines were designed to
develop 10,000 horse-power, driving the ship at the rate of 16-1/2
statute miles an hour.
[Illustration: FIG. 146.--The Great Eastern.]
The figures quoted in the descriptions of these great steamships do
not enable the non-professional reader to form a conception of the
wonderful power which is concentrated within so small a space as is
occupied by their steam-machinery. The "horse-power" of the engines is
that determined by James Watt as the maximum obtainable for eight
hours a day from the strongest London draught-horses. The ordinary
average draught-horse would hardly be able to exert two-thirds as much
during the eight hours' steady work of a working-day. The working-day
of the steam-engine, on the other hand, is twenty-four hours in
length.
[Illustration: FIG. 147.--The Great Eastern at Sea.]
The work of the 10,000 horse-power engines of the Great Eastern could
be barely equaled by the efforts of 15,000 horses; but to continue
their work uninterruptedly, day in and day out, for weeks together, as
when done by steam, would require at least three relays, or 45,000
horses. Such a stud would weigh 25,000 tons, and if harnessed "tandem"
would extend thirty miles. It is only by such a comparison that the
mind can begin to comprehend the utter impossibility of accomplishing
by means of animal power the work now done for the world by steam.
The cost of the greater power is but about one-tenth that of
horse-power, and by its means tasks are accomplished with ease which
are absolutely impossible of accomplishment by animal power.
It is estimated that the total steam-power of the world is about
15,000,000 horse-power, and that, were horses actually employed to do
the work which these engines would be capable of doing were they kept
constantly in operation, the number required would exceed 60,000,000.
Thus, from the small beginnings of the Comte d'Auxiron and the Marquis
de Jouffroy in France, of Symmington in Great Britain, and of Henry,
Rumsey, and Fitch, and of Fulton and Stevens, in the United States,
steam-navigation has grown into a great and inestimable aid and
blessing to mankind.
We to-day cross the ocean with less risk, and transport ourselves and
our goods at as little cost in either time or money as, at the
beginning of the century, our parents experienced in traveling
one-tenth the distance.
It is largely in consequence of this ingenious application of a power
that reminds one of the fabled genii of Eastern romance, that the
mechanic and the laborer of to-day enjoy comforts and luxuries that
were denied to wealth, and to royalty itself, a century ago.
The magnitude of our modern steamships excites the wonder and
admiration of even the people of our own time; and there is certainly
no creation of art that can be grander in appearance than a
transatlantic steamer a hundred and fifty yards in length, and
weighing, with her stores, five or six thousand tons, as she starts on
her voyage, moved by engines equal in power to the united strength of
thousands of horses; none can more fully awaken a feeling of awe than
an immense structure like the great modern iron-clads (Fig. 145),
vessels having a total weight of 8,000 to 10,000 tons, and propelled
by steam-engines of as many horse-power, carrying guns whose shot
penetrate solid iron 20 inches thick, and having a power of impact,
when steaming at moderate speed, sufficient to raise 35,000 tons a
foot high.
Far more huge than the Monarch among the iron-clads even is that
prematurely-built monster, the Great Eastern (Fig. 147), already
described, an eighth of a mile long, and with steam doing the work of
a stud of 45,000 horses.
Thus we are to-day witnessing the literal fulfillment of the
predictions of Oliver Evans and of John Stevens, and almost that
contained in the couplets written by the poet Darwin, who, more than a
century ago, before even the earliest of Watt's improvements had
become generally known, sang:
"Soon shall thy arm, unconquered Steam, afar
Drag the slow barge, or drive the rapid car;
Or, on wide-waving wings expanded, bear
The flying chariot through the fields of air."
[Illustration]
CHAPTER VII.
_THE PHILOSOPHY OF THE STEAM-ENGINE._
THE HISTORY OF ITS GROWTH; ENERGETICS AND THERMO-DYNAMICS.
"Of all the features which characterize this progressive economical
movement of civilized nations, that which first excites attention,
through its intimate connection with the phenomena of production, is
the perpetual and, so far as human foresight can extend, the
unlimited growth of man's power over Nature. Our knowledge of the
properties and laws of physical objects shows no sign of approaching
its ultimate boundaries; it is advancing more rapidly, and in a
greater number of directions at once, than in any previous age or
generation, and affording such frequent glimpses of unexplored
fields beyond as to justify the belief that our acquaintance with
Nature is still almost in its infancy."--MILL.
The growth of the philosophy of the steam-engine presents as
interesting a study as that of the successive changes which have
occurred in its mechanism.
In the operation of the steam-engine we find illustrated many of the
most important principles and facts which constitute the physical
sciences. The steam-engine is an exceedingly ingenious, but,
unfortunately, still very imperfect, machine for transforming the
heat-energy obtained by the chemical combination of a combustible with
the supporter of combustion into mechanical energy. But the original
source of all this energy is found far back of its first appearance in
the steam-boiler. It had its origin at the beginning, when all Nature
came into existence. After the solar system had been formed from the
nebulous chaos of creation, the glowing mass which is now called the
sun was the depository of a vast store of heat-energy, which was
thence radiated into space and showered upon the attendant worlds in
inconceivable quantity and with unmeasured intensity. During the past
life of the globe, the heat-energy received from the sun upon the
earth's surface was partly expended in the production of great
forests, and the storage, in the trunks, branches, and leaves of the
trees of which they were composed, of an immense quantity of carbon,
which had previously existed in the atmosphere, combined with oxygen,
as carbonic acid. The great geological changes which buried these
forests under superincumbent strata of rock and earth resulted in the
formation of coal-beds, and the storage, during many succeeding ages,
of a vast amount of carbon, of which the affinity for oxygen remained
unsatisfied until finally uncovered by the hand of man. Thus we owe to
the heat and light of the sun, as was pointed out by George
Stephenson, the incalculable store of potential energy upon which the
human race is so dependent for life and all its necessaries, comforts,
and luxuries.
This coal, thrown upon the grate in the steam-boiler, takes fire, and,
uniting again with the oxygen, sets free heat in precisely the same
quantity that it was received from the sun and appropriated during the
growth of the tree. The actual energy thus rendered available is
transferred, by conduction and radiation, to the water in the
steam-boiler, converts it into steam, and its mechanical effect is
seen in the expansion of the liquid into vapor against the
superincumbent pressure. Transferred from the boiler to the engine,
the steam is there permitted to expand, doing work, and the
heat-energy with which it is charged becomes partly converted into
mechanical energy, and is applied to useful work in the mill or to
driving the locomotive or the steamboat.
Thus we may trace the store of energy received from the sun and
contained in our coal through its several changes until it is finally
set at work; and we might go still further and observe how, in each
case, it is again usually re-transformed and again set free as
heat-energy.
The transformation which takes place in the furnace is a chemical
change; the transfer of heat to the water and the subsequent phenomena
accompanying its passage through the engine are physical changes, some
of which require for their investigation abstruse mathematical
operations. A thorough comprehension of the principles governing the
operation of the steam-engine, therefore, can only be attained after
studying the phenomena of physical science with sufficient minuteness
and accuracy to be able to express with precision the laws of which
those sciences are constituted. The study of the philosophy of the
steam-engine involves the study of chemistry and physics, and of the
new science of energetics, of which the now well-grown science of
thermo-dynamics is a branch. This sketch of the growth of the
steam-engine may, therefore, be very properly concluded by an outline
of the growth of the several sciences which together make up its
philosophy, and especially of the science of thermo-dynamics, which is
peculiarly the science of the steam-engine and of the other
heat-engines.
These sciences, like the steam-engine itself, have an origin which
antedates the commencement of the Christian era; but they grew with an
almost imperceptible growth for many centuries, and finally, only a
century ago, started onward suddenly and rapidly, and their progress
has never since been checked. They are now fully-developed and
well-established systems of natural philosophy. Yet, like that of the
steam-engine and of its companion heat-engines, their growth has by no
means ceased; and, while the student of science cannot do more than
indicate the direction of their progress, he can readily believe that
the beginning of the end is not yet reached in their movement toward
completeness, either in the determination of facts or in the
codification of their laws.
When Hero lived at Alexandria, the great "Museum" was a most important
centre, about which gathered the teachers of all then known
philosophies and of all the then recognized but unformed sciences, as
well as of all those technical branches of study which had already
been so far developed as to be capable of being systematically taught.
Astronomical observations had been made regularly and uninterruptedly
by the Chaldean astrologers for two thousand years, and records
extending back many centuries had been secured at Babylon by
Calisthenes and given to Aristotle, the father of our modern
scientific method. Ptolemy had found ready to his hand the records of
Chaldean observers of eclipses extending back nearly 650 years, and
marvelously accurate.[103]
[103] Their estimate of the length of the Saros, or cycle of
eclipses--over 19 years--was "within 19-1/2 minutes of the
truth."--DRAPER.
A rude method of printing with an engraved roller on plastic clay,
afterward baked, thus making up ceramic libraries, was practised long
previous to this time; and in the alcoves in which Hero worked were
many of these books of clay.
This great Library and Museum of Alexandria was founded three
centuries before the birth of Christ, by Ptolemy Soter, who
established as his capital that great Egyptian city when the death of
his brother, the youthful but famous conqueror whose name he gave it,
placed him upon the throne of the colossal successor of the then
fallen Persian Empire. The city itself, embellished with every
ornament and provided with every luxury that the wealth of a conquered
world or the skill, taste, and ingenuity of the Greek painters,
sculptors, architects, and engineers could provide, was full of
wonders; it was a wonder in itself. This rich, populous, and
magnificent city was the metropolis of the then civilized world.
Trade, commerce, manufactures, and the fine arts were all represented
in this splendid exchange, and learning found its most acceptable
home and noblest field within the walls of Ptolemy's Museum; its
disciples found themselves welcomed and protected by its founder and
his successors, Philadelphus and the later Ptolemies.
The Alexandrian Museum was founded with the declared object of
collecting all written works of authority, of promoting the study of
literature and art, and of stimulating and assisting experimental and
mathematical scientific investigation and research. The founders of
modern libraries, colleges, and technical schools have their prototype
in intelligence, public spirit, and liberality, in the first of the
Ptolemies, who not only spent an immense sum in establishing this
great institution, but spared no expense in sustaining it. Agents were
sent out into all parts of the world, purchasing books. A large staff
of scribes was maintained at the museum, whose duty it was to multiply
copies of valuable works, and to copy for the library such works as
could not be purchased.
The faculty of the museum was as carefully organized as was the plan
of its administration. The four principal faculties of astronomy,
literature, mathematics, and medicine were subdivided into sections
devoted to the several branches of each department. The collections of
the museum were as complete as the teachers of the undeveloped
sciences of the time could make them. Lectures were given in all
branches of study, and the number of students was sometimes as great
as twelve or thirteen thousand. The number of books which were
collected here, when the barbarian leaders of the Roman troops under
Caesar burned the greater part of it, was stated to be 700,000. Of
these, 400,000 were within the museum itself, and were all destroyed;
the rest were in the temple of Serapis, and, for the time, escaped
destruction.
The greatest of all the great men who lived at Alexandria at the time
of the establishment of the museum was Aristotle, the teacher of
Alexander and the friend of Ptolemy. It is to Aristotle that we owe
the systematization of the philosophical ideas of Plato and the
creation of the inductive method, in which has originated all modern
science. It is to the learned men of Alexandria that we are indebted
for so effective an application of the Aristotelian philosophy that
all the then known sciences were given form, and were so thoroughly
established that the work of modern science has been purely one of
development.
The inductive method, which built up all the older sciences, and which
has created all those of recent development, consists, first, in the
discovery and quantitative determination of facts; secondly, when a
sufficient number of facts have been thus observed and defined, in the
grouping of those facts, and the detection, by a study of their mutual
relations, of the natural laws which give rise to or regulate them.
This simple method is that--and the only--method by which science
advances. By this method, and by it only, do we acquire connected and
systematic knowledge of all the phenomena of Nature of which the
physical sciences are cognizant. It is only by the application of this
Aristotelian method and philosophy that we can hope to acquire exact
scientific knowledge of existing phenomena, or to become able to
anticipate the phenomena which are to distinguish the future. The
Aristotelian method of observing facts, and of inductive reasoning
with those facts as a basis, has taught the chemist the properties of
the known elementary substances and their characteristic behavior
under ascertained conditions, and has taught him the laws of
combination and the effects of their union, enabling him to predict
the changes and the phenomena, chemical and physical, which inevitably
follow their contact under any specified set of conditions.
It is this process which has enabled the physicist to ascertain the
methods of molecular motion which give us light, heat, or electricity,
and the range of action and the laws which govern the transfer of
energy from one of these modes of motion to another. It was this
method of study which enabled James Watt to detect and to remedy the
defects of the Newcomen engine, and it is by the Aristotelian
philosophy that the engineer of to-day is taught to construct the
modern steamship, and to predict, before the keel is laid or a blow
struck in the workshop or the ship-yard, what will be the weight of
the vessel, its cargo-carrying capacity, the necessary size and power
of its engines, the quantity of coal which they will require per day
while crossing the ocean, the depth at which the great hull will float
in the water, and the exact speed that the vessel will attain when the
engines are exerting their thousand or their ten thousand horse-power.
It was at Alexandria that this mighty philosophy was first given a
field in which to work effectively. Here Ptolemy studied astronomy and
"natural philosophy;" Archimedes applied himself to the studies which
attract the mathematician and engineer; Euclid taught his royal pupil
those elements of geometry which have remained standard twenty-two
centuries; Eratosthenes and Hipparchus studied and taught astronomy,
and inaugurated the existing system of quantitative investigation,
proving the spherical form of the earth; and Ctesibius and Hero
studied pneumatics and experimented with the germs of the steam-engine
and of less important machines.
When, seven centuries later, the destruction of this splendid
institution was signalized by the death of that brilliant scholar and
heathen teacher of philosophy, Hypatia, at the hands of the more
heathenish fanatics who tore her in pieces at the foot of the cross,
and by the dispersion of the library left by Caesar's soldiers in the
Serapeum, a true philosophy had been created, and the inductive method
was destined to live and to overcome every obstacle in the path of
enlightenment and civilization. The fall of the Alexandrian Museum,
sad as was the event, could not destroy the new philosophical method.
Its fruits ripened slowly but surely, and we are to-day gathering a
plentiful harvest.
Science, literature, and the arts, all remained dormant for several
centuries after the catastrophe which deprived them of the light in
which they had flourished so many centuries. The armies of the caliphs
made complete the shameful work of destruction begun by the armies of
Caesar, and the Alexandrian Library, partly destroyed by the Romans,
was completely dispersed by the Patriarchs and their ignorant and
fanatical followers; and finally all the scattered remnants were
burned by the Saracens. But when the thirst for conquest had become
satiated or appeased, the followers of the caliphs turned their
attention to intellectual pursuits, and the ninth century of the
Christian era saw once more such a collection of philosophical
writings, collected at Bagdad, as could only be gathered by the power
and wealth of the later conquerors of the world. Philosophy once again
resumed its empire, and another race commenced the study of the
mathematics of India and of Greece, the astronomy of Chaldea, and of
all the sciences which originated in Greece and in Egypt. By the
conquest of Spain by the Saracens, the new civilization was imported
into Western Europe and libraries were gathered together under the
Moorish rulers, one of which numbered more than a half-million
volumes. Wherever Saracen armies had extended Mohammedan rule,
schools and colleges, libraries and collections of philosophical
apparatus, were scattered in strange profusion; and students,
teachers, philosophers, of all--the speculative as well as the
Aristotelian--schools, gathered together at these intellectual
ganglia, as enthusiastic in their work as were their Alexandrian
predecessors. The endowment of colleges, that truest gauge of the
intelligence of the wealthy classes of any community, became as
common--perhaps more so--as at the present time, and provision was
made for the education of rich and poor alike. The mathematical
sciences, and the wonderful and beautiful phenomena which--but a
thousand years later--were afterward grouped into a science and called
chemistry, were especially attractive to the Arabian scholars, and
technical applications of discovered facts and laws assisted in a
wonderfully rapid development of arts and manufactures.
When, a thousand years after Christ, the centre of intellectual
activity and of material civilization had drifted westward into
Andalusia, the foundation of every modern physical science except that
now just taking shape--the all-grasping science of energetics--had
been laid with experimentally derived facts; and in mathematics there
had been erected a symmetrical and elegant superstructure. Even that
underlying principle of all the sciences, the principle of the
persistence of energy, had been, perhaps unwittingly, enunciated.
Distinguished historians have shown how the progress of civilization
in Europe resulted in the creation, during the middle ages, of the now
great middle class, which, holding the control of political power,
governs every civilized nation, and has come into power so gradually
that it was only after centuries that its influence was seen and felt.
This, which Buckle[104] calls the intellectual class, first became
active, independently of the military and of the clergy, in the
fourteenth century. In the two succeeding centuries this class gained
power and influence; and in the seventeenth century we find a
magnificent advance in all branches of science, literature, and art,
marking the complete emancipation of the intellect from the artificial
conditions which had so long repressed its every effort at
advancement.
[104] "History of Civilization in England," vol. i., p. 208. London,
1868.
Another great social revolution thus occurred, following another
period of centuries of intellectual stagnation. The Saracen invaders
were driven from Europe; the Crusaders invaded Palestine, in the vain
effort to recover from the hands of the infidels the Holy Sepulchre
and the Holy Land; and intestine broils and inter-state conflicts, as
well as these greater social movements, withdrew the minds of men once
more from the arts of peace and the pursuits of scholars. It is not,
then, until the beginning of the seventeenth century--the time of
Galileo and of Newton--that we find the nations of Europe sufficiently
quiet and secure to permit general attention to intellectual
vocations, although it was a half-century earlier (1543) that
Copernicus left to the world that legacy which revolutionized the
theories of the astronomers and established as correct the hypothesis
which made the sun the centre of the solar system.
Galileo now began to overturn the speculations of the deductive
philosophers, and to proclaim the still disputed principle that the
book of Nature is a trustworthy commentary in the study of theological
and revealed truths, so far as they affect or are affected by science;
he suffered martyrdom when he proclaimed the fact that God's laws, as
they now stand, had been instituted without deference to the
preconceived notions of the most ignorant of men. Bruno had a few
years earlier (1600) been burned at the stake for a similar offense.
Galileo was perhaps the first, too, to combine invariably in
application the idea of Plato, the philosophy of Aristotle, and the
methods of modern experimentation, to form the now universal
scientific method of experimental philosophy. He showed plainly how
the grouping of ascertained facts, in natural sequence, leads to the
revelation of the law of that sequence, and indicated the existence of
a principle which is now known as the law of continuity--the law that
in all the operations of Nature there is to be seen an unbroken chain
of effect leading from the present back into a known or an unknown
past, toward a cause which may or may not be determinable by science
or known to history.
Galileo, the Italian, was worthily matched by Newton, the prince of
English philosophers. The science of theoretical mechanics was hardly
beginning to assume the position which it was afterward given among
the sciences; and the grand work of collating facts already
ascertained, and of definitely stating principles which had previously
been vaguely recognized, was splendidly done by Newton. The needs of
physical astronomy urged this work upon him.
Da Vinci had, in the latter half of the fifteenth century, summarized
as much of the statics of mechanical philosophy as had, up to his
time, been given shape; he also rewrote and added very much to what
was known on the subject of friction, and enunciated its laws. He had
evidently a good idea of the principle of "virtual velocities," that
simple case of equivalence of work, in a connected system, which has
done such excellent service since; and with his mechanical philosophy
this versatile engineer and artist curiously mingled much of physical
science. Then Stevinus, the "brave engineer of Bruges," a hundred
years later (1586), alternating office and field work, somewhat after
the manner of the engineer of to-day, wrote a treatise on mechanics,
which showed the value of practical experience and judgment in even
scientific work. And thus the path had been cleared for Newton.
Meantime, also, Kepler had hit upon the true relations of the
distances of the planets and their periodic times, after spending half
a generation in blindly groping for them, thus furnishing those great
landmarks of fact in the mechanics of astronomy; and Galileo had
enunciated the laws of motion. Thus the foundation of the science of
dynamics, as distinguished from statics, was laid, and the beginning
was made of that later science of energetics, of which the philosophy
of the steam-engine is so largely constituted.
Hooke, Huyghens, and others, had already seen some of the principal
consequences of these laws; but it remained for Newton to enunciate
them with the precision of a true mathematician, and to base upon them
a system of dynamical laws, which, complemented by his announcement of
the existence of the force of gravitation, and his statement of its
laws, gave a firm basis for all that the astronomer has since done in
those quantitative determinations of size, weight, and distance, and
of the movements of the heavenly bodies, which compel the wonder and
admiration of mankind.
The Arabians and Greeks had noticed that the direction taken by a body
falling under the action of gravitation was directly toward the centre
of the earth, wherever its fall might occur; Galileo had shown, by his
experiments at Pisa, that the velocity of fall, second after second,
varied as the numbers 1, 3, 5, 7, 9, etc., and that the distances
varied as the squares of the total periods of time during which the
body was falling, and that it was, in British feet, very nearly
sixteen times the square of that time in seconds. Kepler had proved
that the movements of the heavenly bodies were just such as would
occur under the action of central attractive forces and of centrifugal
force.
Putting all these things together, Newton was led to believe that
there existed a "force of gravity," due to the attraction, by the
great mass of the earth, of its own particles and of neighboring
bodies, like the moon, of which force the influence extended as far,
at least, as the latter. He calculated the motion of the earth's
satellite, on the assumption that his theory and the then accepted
measurements of the earth's dimensions were correct, and obtained a
roughly approximate result. Later, in 1679, he revised his
calculations, using Picard's more accurate determination of the
dimensions of the earth, and obtained a result which precisely tallied
with careful measurements, made by the astronomers, of the moon's
motion.
The science of mechanics had now, with the publication of Newton's
"Principia," become thoroughly consistent and logically complete, so
far as was possible without a knowledge of the principles of
energetics; and Newton's enunciations of the laws of motion, concise
and absolutely perfect as they still seem, were the basis of the whole
science of dynamics, as applied to bodies moving freely under the
action of applied forces, either constant or variable. They are as
perfect a basis for that science as are the primary principles of
geometry for the whole beautiful structure which is built up on them.
The three perfect qualitative expressions of dynamical law are:
1. Every free body continues in the state in which it may be, whether
of rest or of rectilinear uniform motion, until compelled to deviate
from that state by impressed forces.
2. Change of motion is proportional to the force impressed, and in the
direction of the right line in which that force acts.
3. Action is always opposed by reaction; action and reaction are
equal, and in directly contrary directions.
We may add to these principles a definition of a force, which is
equally and absolutely complete:
_Force_ is that which produces, or tends to produce, motion, or change
of motion, in bodies. It is measured statically by the weight that
will counterpoise it, or by the pressure which it will produce, and
dynamically by the velocity which it will produce, acting in the unit
of time on the unit of mass.
The quantitative determinations of dynamic effects of forces are
always readily made when it is remembered that the effect of a force
equal to its own weight, when the body is free to move, is to produce
in one second a velocity of 32.2 feet per second, which quantity is
the unit of dynamic measurement.
_Work_ is the product of the resistance met in any instance of the
exertion of a force, into the distance through which that force
overcomes the resistance.
_Energy_ is the work which a body is capable of doing, by its weight
or inertia, under given conditions. The energy of a falling body, or
of a flying shot, is about 1/64 its weight multiplied by the square of
its velocity, or, which is the same thing, the product of its weight
into the height of fall or height due its velocity. These principles
and definitions, with the long-settled definitions of the primary
ideas of space and time, were all that were needed to lead the way to
that grandest of all physical generalizations, the doctrine of the
persistence or conservation of all energy, and to its corollary
declaring the equivalence of all forms of energy, and also to the
experimental demonstration of the transformability of energy from one
mode of existence to another, and its universal existence in the
various modes of motion of bodies and of their molecules.
Experimental physical science had hardly become acknowledged as the
only and the proper method of acquiring knowledge of natural phenomena
at the time of Newton; but it soon became a generally accepted
principle. In physics, Gilbert had made valuable investigations before
Newton, and Galileo's experiments at Pisa had been examples of
similarly useful research. In chemistry, it was only when, a century
later, Lavoisier showed by his splendid example what could be done by
the skillful and intelligent use of quantitative measurements, and
made the balance the chemist's most important tool, that a science was
formed comprehending all the facts and laws of chemical change and
molecular combination. We have already seen how astronomy and
mathematics together led philosophers to the creation and the study of
what finally became the science of mechanics, when experiment and
observation were finally brought to their aid. We can now see how, in
all these physical sciences, four primitive ideas are comprehended:
matter, force, motion, and space--which latter two terms include all
relations of position.
Based on these notions, the science of mechanics comprehends four
sections, which are of general application in the study of all
physical phenomena. These are:
_Statics_, which treats of the action and effect of forces.
_Kinematics_, which treats of relations of motion simply.
_Dynamics_, or kinetics, which treats of simple motion as an effect of
the action of forces.
_Energetics_, which treats of modifications of energy under the action
of forces, and of its transformation from one mode of manifestation to
another, and from one body to another.
Under the latter of these four divisions of mechanical philosophy is
comprehended that latest of the minor sciences, of which the
heat-engines, and especially the steam-engine, illustrate the most
important applications--_Thermo-dynamics_. This science is simply a
wider generalization of principles which, as we have seen, have been
established one at a time, and by philosophers widely separated both
geographically and historically, by both space and time, and which
have been slowly aggregated to form one after another of the sciences,
and out of which, as we now are beginning to see, we are slowly
evolving wider generalizations, and thus tending toward a condition of
scientific knowledge which renders more and more probable the truth of
Cicero's declaration: "One eternal and immutable law embraces all
things and all times." At the basis of the whole science of energetics
lies a principle which was enunciated before Science had a birthplace
or a name:
_All that exists, whether matter or force, and in whatever form, is
indestructible, except by the Infinite Power which has created it._
That matter is indestructible by finite power became admitted as soon
as the chemists, led by their great teacher Lavoisier, began to apply
the balance, and were thus able to show that in all chemical change
there occurs only a modification of form or of combination of
elements, and no loss of matter ever takes place. The "persistence" of
energy was a later discovery, consequent largely upon the experimental
determination of the convertibility of heat-energy into other forms
and into mechanical work, for which we are indebted to Rumford and
Davy, and to the determination of the quantivalence anticipated by
Newton, shown and calculated approximately by Colding and Mayer, and
measured with great probable accuracy by Joule.
[Illustration: Benjamin Thompson, Count Rumford.]
The great fact of the conservation of energy was loosely stated by
Newton, who asserted that the work of friction and the _vis viva_ of
the system or body arrested by friction were equivalent. In 1798,
Benjamin Thompson, Count Rumford, an American who was then in the
Bavarian service, presented a paper[105] to the Royal Society of Great
Britain, in which he stated the results of an experiment which he had
recently made, proving the immateriality of heat and the
transformation of mechanical into heat energy. This paper is of very
great historical interest, as the now accepted doctrine of the
persistence of energy is a generalization which arose out of a series
of investigations, the most important of which are those which
resulted in the determination of the existence of a definite
quantivalent relation between these two forms of energy and a
measurement of its value, now known as the "mechanical equivalent of
heat." His experiment consisted in the determination of the quantity
of heat produced by the boring of a cannon at the arsenal at Munich.
[105] "Philosophical Transactions," 1798.
Rumford, after showing that this heat could not have been derived from
any of the surrounding objects, or by compression of the materials
employed or acted upon, says: "It appears to me extremely difficult,
if not impossible, to form any distinct idea of anything capable of
being excited and communicated in the manner that heat was excited and
communicated in these experiments, except it be motion."[106] He then
goes on to urge a zealous and persistent investigation of the laws
which govern this motion. He estimates the heat produced by a power
which he states could easily be exerted by one horse, and makes it
equal to the "combustion of nine wax candles, each three-quarters of
an inch in diameter," and equivalent to the elevation of "25.68 pounds
of ice-cold water" to the boiling-point, or 4,784.4 heat-units.[107]
The time was stated at "150 minutes." Taking the actual power of
Rumford's Bavarian "one horse" as the most probable figure, 25,000
pounds raised one foot high per minute,[108] this gives the
"mechanical equivalent" of the foot-pound as 783.8 heat-units,
differing but 1.5 per cent. from the now accepted value.
[106] This idea was not by any means original with Rumford. Bacon
seems to have had the same idea; and Locke says, explicitly enough:
"Heat is a very brisk agitation of the insensible parts of the
object ... so that what in our sensation is heat, in the object is
nothing but motion."
[107] The British heat-unit is the quantity of heat required to heat
one pound of water 1 deg. Fahr. from the temperature of maximum density.
[108] Rankine gives 25,920 foot-pounds per minute--or 432 per
second--for the average draught-horse in Great Britain, which is
probably too high for Bavaria. The engineer's "horse-power"--33,000
foot-pounds per minute--is far in excess of the average power of
even a good draught-horse, which latter is sometimes taken as
two-thirds the former.
Had Rumford been able to eliminate all losses of heat by evaporation,
radiation, and conduction, to which losses he refers, and to measure
the power exerted with accuracy, the approximation would have been
still closer. Rumford thus made the experimental discovery of the real
nature of heat, proving it to be a form of energy, and, publishing
the fact a half-century before the now standard determinations were
made, gave us a very close approximation to the value of the
heat-equivalent. Rumford also observed that the heat generated was
"exactly proportional to the force with which the two surfaces are
pressed together, and to the rapidity of the friction," which is a
simple statement of equivalence between the quantity of work done, or
energy expended, and the quantity of heat produced. This was the first
great step toward the formation of a Science of Thermo-dynamics.
Rumford's work was the corner-stone of the science.
Sir Humphry Davy, a little later (1799), published the details of an
experiment which conclusively confirmed these deductions from
Rumford's work. He rubbed two pieces of ice together, and found that
they were melted by the friction so produced. He thereupon concluded:
"It is evident that ice by friction is converted into water....
Friction, consequently, does not diminish the capacity of bodies for
heat."
Bacon and Newton, and Hooke and Boyle, seem to have anticipated--long
before Rumford's time--all later philosophers, in admitting the
probable correctness of that modern dynamical, or vibratory, theory of
heat which considers it a mode of motion; but Davy, in 1812, for the
first time, stated plainly and precisely the real nature of heat,
saying: "The immediate cause of the phenomenon of heat, then, is
motion, and the laws of its communication are precisely the same as
the laws of the communication of motion." The basis of this opinion
was the same that had previously been noted by Rumford.
So much having been determined, it became at once evident that the
determination of the exact value of the mechanical equivalent of heat
was simply a matter of experiment; and during the succeeding
generation this determination was made, with greater or less
exactness, by several distinguished men. It was also equally evident
that the laws governing the new science of thermo-dynamics could be
mathematically expressed.
Fourier had, before the date last given, applied mathematical analysis
in the solution of problems relating to the transfer of heat without
transformation, and his "Theorie de la Chaleur" contained an
exceedingly beautiful treatment of the subject. Sadi Carnot, twelve
years later (1824), published his "Reflexions sur la Puissance Motrice
du Feu," in which he made a first attempt to express the principles
involved in the application of heat to the production of mechanical
effect. Starting with the axiom that a body which, having passed
through a series of conditions modifying its temperature, is returned
to "its primitive physical state as to density, temperature, and
molecular constitution," must contain the same quantity of heat which
it had contained originally, he shows that the efficiency of
heat-engines is to be determined by carrying the working fluid through
a complete cycle, beginning and ending with the same set of
conditions. Carnot had not then accepted the vibratory theory of heat,
and consequently was led into some errors; but, as will be seen
hereafter, the idea just expressed is one of the most important
details of a theory of the steam-engine.
Seguin, who has already been mentioned as one of the first to use the
fire-tubular boiler for locomotive engines, published in 1839 a work,
"Sur l'Influence des Chemins de Fer," in which he gave the requisite
data for a rough determination of the value of the mechanical
equivalent of heat, although he does not himself deduce that value.
Dr. Julius R. Mayer, three years later (1842), published the results
of a very ingenious and quite closely approximate calculation of the
heat-equivalent, basing his estimate upon the work necessary to
compress air, and on the specific heats of the gas, the idea being
that the work of compression is the equivalent of the heat generated.
Seguin had taken the converse operation, taking the loss of heat of
expanding steam as the equivalent of the work done by the steam while
expanding. The latter also was the first to point out the fact,
afterward experimentally proved by Hirn, that the fluid exhausted from
an engine should heat the water of condensation less than would the
same fluid when originally taken into the engine.
A Danish engineer, Colding, at about the same time (1843), published
the results of experiments made to determine the same quantity; but
the best and most extended work, and that which is now almost
universally accepted as standard, was done by a British investigator.
James Prescott Joule commenced the experimental investigations which
have made him famous at some time previous to 1843, at which date he
published, in the _Philosophical Magazine_, his earliest method. His
first determination gave 770 foot-pounds. During the succeeding five
or six years Joule repeated his work, adopting a considerable variety
of methods, and obtaining very variable results. One method was to
determine the heat produced by forcing air through tubes; another, and
his usual plan, was to turn a paddle-wheel by a definite power in a
known weight of water. He finally, in 1849, concluded these
researches.
[Illustration: James Prescott Joule.]
The method of calculating the mechanical equivalent of heat which was
adopted by Dr. Mayer, of Heilbronn, is as beautiful as it is
ingenious: Conceive two equal portions of atmospheric air to be
inclosed, at the same temperature--as at the freezing-point--in
vessels each capable of containing one cubic foot; communicate heat to
both, retaining the one portion at the original volume, and permitting
the other to expand under a constant pressure equal to that of the
atmosphere. In each vessel there will be inclosed 0.08073 pound, or
1.29 ounce, of air. When, at the same temperature, the one has doubled
its pressure and the other has doubled its volume, each will be at a
temperature of 525.2 deg. Fahr., or 274 deg. C, and each will have double the
original temperature, as measured on the absolute scale from the zero
of heat-motion. But the one will have absorbed but 6-3/4 British
thermal units, while the other will have absorbed 9-1/2. In the first
case, all of this heat will have been employed in simply increasing
the temperature of the air; in the second case, the temperature of the
air will have been equally increased, and, besides, a certain amount
of work--2,116.3 foot-pounds--must have been done in overcoming the
resistance of the air; it is to this latter action that we must debit
the additional heat which has disappeared. Now, 2,116.3/(2-3/4) = 770
foot-pounds per heat-unit--almost precisely the value derived from
Joule's experiments. Had Mayer's measurement been absolutely accurate,
the result of his calculation would have been an exact determination
of the heat-equivalent, provided no heat is, in this case, lost by
internal work.
Joule's most probably accurate measure was obtained by the use of a
paddle-wheel revolving in water or other fluid. A copper vessel
contained a carefully weighed portion of the fluid, and at the bottom
was a step, on which stood a vertical spindle carrying the
paddle-wheel. This wheel was turned by cords passing over
nicely-balanced grooved wheels, the axles of which were carried on
friction-rollers. Weights hung at the ends of these cords were the
moving forces. Falling to the ground, they exerted an easily and
accurately determinable amount of work, _W_ x _H_, which turned the
paddle-wheel a definite number of revolutions, warming the water by
the production of an amount of heat exactly equivalent to the amount
of work done. After the weight had been raised and this operation
repeated a sufficient number of times, the quantity of heat
communicated to the water was carefully determined and compared with
the amount of work expended in its development. Joule also used a pair
of disks of iron rubbing against each other in a vessel of mercury,
and measured the heat thus developed by friction, comparing it with
the work done. The average of forty experiments with water gave the
equivalent 772.692 foot-pounds; fifty with mercury gave 774.083;
twenty with cast-iron gave 774.987--the temperature of the apparatus
being from 55 deg. to 60 deg. Fahr.
Joule also determined, by experiment, the fact that the expansion of
air or other gas without doing work produces no change of temperature,
which fact is predicable from the now known principles of
thermo-dynamics. He stated the results of his researches relating to
the mechanical equivalent of heat as follows:
1. The heat produced by the friction of bodies, whether solid or
liquid, is always proportional to the quantity of work expended.
2. The quantity required to increase the temperature of a pound of
water (weighed _in vacuo_ at 55 deg. to 60 deg. Fahr.) by one degree requires
for its production the expenditure of a force measured by the fall of
772 pounds from a height of one foot. This quantity is now generally
called "Joule's equivalent."
During this series of experiments, Joule also deduced the position of
the "absolute zero," the point at which heat-motion ceases, and stated
it to be about 480 deg. Fahr. below the freezing-point of water, which is
not very far from the probably true value,-493.2 deg. Fahr. (-273 deg. C.), as
deduced afterward from more precise data.
The result of these, and of the later experiments of Hirn and others,
has been the admission of the following principle:
Heat-energy and mechanical energy are mutually convertible and have a
definite equivalence, the British thermal unit being equivalent to 772
foot-pounds of work, and the metric _calorie_ to 423.55, or, as
usually taken, 424 kilogrammetres. The exact measure is not fully
determined, however.
It has now become generally admitted that all forms of energy due to
physical forces are mutually convertible with a definite
quantivalence; and it is not yet determined that even vital and mental
energy do not fall within the same great generalization. This
quantivalence is the sole basis of the science of Energetics.
The study of this science has been, up to the present time,
principally confined to that portion which comprehends the relations
of heat and mechanical energy. In the study of this department of the
science, thermo-dynamics, Rankine, Clausius, Thompson, Hirn, and
others have acquired great distinction. In the investigations which
have been made by these authorities, the methods of transfer of heat
and of modification of physical state in gases and vapors, when a
change occurs in the form of the energy considered, have been the
subjects of especial study.
According to the law of Boyle and Marriotte, the expansion of such
fluids follows a law expressed graphically by the hyperbola, and
algebraically by the expression PV^{_x_} = A, in which, with
unchanging temperature, _x_ is equal to 1. One of the first and most
evident deductions from the principles of the equivalence of the
several forms of energy is that the value of x must increase as the
energy expended in expansion increases. This change is very marked
with a vapor like steam--which, expanded without doing work, has an
exponent less than unity, and which, when doing work by expanding
behind a piston, partially condenses, the value of _x_ increases to,
in the case of steam, 1.111 according to Rankine, or, probably more
correctly, to 1.135 or more, according to Zeuner and Grashof. This
fact has an important bearing upon the theory of the steam-engine, and
we are indebted to Rankine for the first complete treatise on that
theory as thus modified.
Prof. Rankine began his investigations as early as 1849, at which time
he proposed his theory of the molecular constitution of matter, now
well known as the theory of molecular vortices. He supposes a system
of whirling rings or vortices of heat-motion, and bases his
philosophy upon that hypothesis, supposing sensible heat to be
employed in changing the velocity of the particles, latent heat to be
the work of altering the dimensions of the orbits, and considering the
effort of each vortex to enlarge its boundaries to be due to
centrifugal force. He distinguished between real and apparent specific
heat, and showed that the two methods of absorption of heat, in the
case of the heating of a fluid, that due to simple increase of
temperature and that due to increase of volume, should be
distinguished; he proposed, for the latter quantity, the term
heat-potential, and for the sum of the two, the name of thermo-dynamic
function.
[Illustration: Prof. W. J. M. Rankine.]
Carnot had stated, a quarter of a century earlier, that the efficiency
of a heat-engine is a function of the two limits of temperature
between which the machine is worked, and not of the nature of the
working substance--an assertion which is quite true where the material
does not change its physical state while working. Rankine now deduced
that "general equation of thermo-dynamics" which expresses
algebraically the relations between heat and mechanical energy, when
energy is changing from the one state to the other, in which equation
is given, for any assumed change of the fluids, the quantity of heat
transformed. He showed that steam in the engine must be partially
liquefied by the process of expanding against a resistance, and proved
that the total heat of a perfect gas must increase with rise of
temperature at a rate proportional to its specific heat under constant
pressure.
Rankine, in 1850, showed the inaccuracy of the then accepted value,
0.2669, of the specific heat of air under constant pressure, and
calculated its value as 0.24. Three years later, the experiments of
Regnault gave the value 0.2379, and Rankine, recalculating it, made it
0.2377. In 1851, Rankine continued his discussion of the subject, and,
by his own theory, corroborated Thompson's law giving the efficiency
of a perfect heat-engine as the quotient of the range of working
temperature to the temperature of the upper limit, measured from the
absolute zero.