same subject, taking quite a different method, studying the mechanical
effects of heat in gases, and deducing, almost simultaneously with
Rankine (1850), the general equation which lies at the beginning of
the theory of the equivalence of heat and mechanical energy. He found
that the probable zero of heat-motion is at such a point that the
Carnot function must be approximately the reciprocal of the "absolute"
temperature, as measured with the air thermometer, or, stated exactly,
that quantity as determined by a perfect gas thermometer. He confirmed
Rankine's conclusion relative to the liquefaction of saturated vapors
when expanding against resistance, and, in 1854, adapted Carnot's
principle to the new theory, and showed that his idea of the
reversible engine and of the performance of a cycle in testing the
changes produced still held good, notwithstanding Carnot's ignorance
of the true nature of heat. Clausius also gave us the extremely
important principle: It is impossible for a self-acting machine,
unaided, to transfer heat from one body at a low temperature to
another having a higher temperature.
Simultaneously with Rankine and Clausius, Prof. William Thomson was
engaged in researches in thermo-dynamics (1850). He was the first to
express the principle of Carnot as adapted to the modern theory by
Clausius in the now generally quoted propositions:[109]
[109] _Vide_ Tait's admirable "Sketch of Thermodynamics," second
edition, Edinburgh, 1877.
1. When equal mechanical effects are produced by purely thermal
action, equal quantities of heat are produced or disappear by
transformation of energy.
2. If, in any engine, a reversal effects complete inversion of all the
physical and mechanical details of its operation, it is a perfect
engine, and produces maximum effect with any given quantity of heat
and with any fixed limits of range of temperature.
William Thomson and James Thompson showed, among the earliest of their
deductions from these principles, the fact, afterward confirmed by
experiment, that the melting-point of ice should be lowered by
pressure 0.0135 deg. Fahr, for each atmosphere, and that a body which
contracts while being heated will always have its temperature
decreased by sudden compression. Thomson applied the principles of
energetics in extended investigations in the department of
electricity, while Helmholtz carried some of the same methods into his
favorite study of acoustics.
The application of now well-settled principles to the physics of gases
led to many interesting and important deductions: Clausius explained
the relations between the volume, density, temperature, and pressure
of gases, and their modifications; Maxwell reestablished the
experimentally determined law of Dalton and Charles, known also as
that of Gay-Lussac (1801), which asserts that all masses of equal
pressure, volume, and temperature, contain equal numbers of molecules.
On the Continent of Europe, also, Hirn, Zeuner, Grashof, Tresca,
Laboulaye, and others have, during the same period and since,
continued and greatly extended these theoretical researches.
During all this time, a vast amount of experimental work has also been
done, resulting in the determination of important data without which
all the preceding labor would have been fruitless. Of those who have
engaged in such work, Cagniard de la Tour, Andrews, Regnault, Hirn,
Fairbairn and Tate, Laboulaye, Tresca, and a few others have directed
their researches in this most important direction with the special
object of aiding in the advancement of the new-born sciences. By the
middle of the present century, the time which we are now studying,
this set of data was tolerably complete. Boyle had, two hundred years
before, discovered and published the law, which is now known by his
name[110] and by that of Marriotte,[111] that the pressure of a gas
varies inversely as its volume and directly as its density; Dr. Black
and James Watt discovered, a hundred years later (1760), the latent
heat of vapors, and Watt determined the method of expansion of steam;
Dalton, in England, and Gay-Lussac, in France, showed, at the
beginning of the nineteenth century, that all gaseous fluids are
expanded by equal fractions of their volume by equal increments of
temperature; Watt and Robison had given tables of the elastic force of
steam, and Gren had shown that, at the temperature of boiling water,
the pressure of steam was equal to that of the atmosphere; Dalton,
Ure, and others proved (1800-1818) that the law connecting
temperatures and pressures of steam was expressed by a geometrical
ratio; and Biot had already given an approximate formula, when
Southern introduced another, which is still in use.
[110] "New Experiments, Physico-Mechanical, etc., touching the
Spring of Air," 1662.
[111] "De la Nature de l'Air," 1676.
The French Government established a commission in 1823 to experiment
with a view to the institution of legislation regulating the working
of steam-engines and boilers; and this commission, MM. de Prony,
Arago, Girard, and Dulong, determined quite accurately the
temperatures of steam under pressures running up to twenty-four
atmospheres, giving a formula for the calculation of the one quantity,
the other being known. Ten years later, the Government of the United
States instituted similar experiments under the direction of the
Franklin Institute.
The marked distinction between gases, like oxygen and hydrogen, and
condensible vapors, like steam and carbonic acid, had been, at this
time, shown by Cagniard de la Tour, who, in 1822, studied their
behavior at high temperatures and under very great pressures. He found
that, when a vapor was confined in a glass tube in presence of the
same substance in the liquid state, as where steam and water were
confined together, if the temperature was increased to a certain
definite point, the whole mass suddenly became of uniform character,
and the previously existing line of demarkation vanished, the whole
mass of fluid becoming, as he inferred, gaseous. It was at about this
time that Faraday made known his then novel experiments, in which
gases which had been before supposed permanent were liquefied, simply
by subjecting them to enormous pressures. He then also first stated
that, above certain temperatures, liquefaction of vapors was
impossible, however great the pressure.
Faraday's conclusion was justified by the researches of Dr. Andrews,
who has since most successfully extended the investigation commenced
by Cagniard de la Tour, and who has shown that, at a certain point,
which he calls the "critical point," the properties of the two states
of the fluid fade into each other, and that, at that point, the two
become continuous. With carbonic acid, this occurs at 75 atmospheres,
about 1,125 pounds per square inch, a pressure which would
counterbalance a column of mercury 60 yards, or nearly as many metres,
high. The temperature at this point is about 90 deg. Fahr., or 31 deg. Cent.
For ether, the temperature is 370 deg. Fahr., and the pressure 38
atmospheres; for alcohol, they are 498 deg. Fahr., and 120 atmospheres;
and for bisulphide of carbon, 505 deg. Fahr., and 67 atmospheres. For
water, the pressure is too high to be determined; but the temperature
is about 775 deg. Fahr., or 413 deg. Cent.
Donny and Dufour have shown that these normal properties of vapors and
liquids are subject to modification by certain conditions, as
previously (1818) noted by Gay-Lussac, and have pointed out the
bearing of this fact upon the safety of steam-boilers. It was
discovered that the boiling-point of water could be elevated far above
its ordinary temperature of ebullition by expedients which deprive the
liquid of the air usually condensed within its mass, and which prevent
contact with rough or metallic surfaces. By suspension in a mixture of
oils which is of nearly the same density, Dufour raised drops of water
under atmospheric pressure to a temperature of 356 deg. Fahr.--180 deg.
Cent.--the temperature of steam of about 150 pounds per square inch.
Prof. James Thompson has, on theoretical grounds, indicated that a
somewhat similar action may enable vapor, under some conditions, to be
cooled below the normal temperature of condensation, without
liquefaction.
Fairbairn and Tate repeated the attempt to determine the volume and
temperature of water at pressures extending beyond those in use in the
steam-engine, and incomplete determinations have also been made by
others.
Regnault is the standard authority on these data. His experiments
(1847) were made at the expense of the French Government, and under
the direction of the French Academy. They were wonderfully accurate,
and extended through a very wide range of temperatures and pressures.
The results remain standard after the lapse of a quarter of a century,
and are regarded as models of precise physical work.[112]
[112] _See_ Porter on the Steam-Engine Indicator for the best set of
Regnault's tables generally accessible.
Regnault found that the total heat of steam is not constant, but that
the latent heat varies, and that the sum of the latent and sensible
heats, or the total heat, increases 0.305 of a degree for each degree
of increase in the sensible heat, making 0.305 the specific heat of
saturated steam. He found the specific heat of superheated steam to be
0.4805.
Regnault promptly detected the fact that steam was not subject to
Boyle's law, and showed that the difference is very marked. In
expressing his results, he not only tabulated them but also laid them
down graphically; he further determined exact constants for Biot's
algebraic expression,
log. _p_ = _a_ - _b_A^{_x_} - _c_B^{_x_};
making _x_ = 20 + _t_ deg. Cent.; _a_ = 6.264035; log. _b_ = 0.1397743;
log. _c_ = 0.6924351; log. A = [=1].9940493, and log. B = [=1].9983439;
_p_ is the pressure in atmospheres. Regnault, in the expression for the
total heat, H = A + _bt_, determined on the centigrade scale [theta] =
606.5 + 0.305 _t_ Cent. For the Fahrenheit scale, we have the
following equivalent expressions:
H = 1,113.44 deg. + 0.305 _t_ deg. Fahr., if measured from 0 deg. Fahr.
= 1,091.9 deg. + 0.305 (_t_ deg. - 32) Fahr.,; } if measured from
= 1,081.94 deg. + 0.305 _t_ deg. Fahr., } the freezing-point.
For latent heat, we have:
L = 606.5 deg. - 0.695 _t_ deg. Cent.
= 1,091.7 deg.- 0.695 (_t_ deg. - 32) Fahr.
= 1,113.94 deg.- 0.695 _t_ deg. Fahr.
Since Regnault's time, nothing of importance has been done in this
direction. There still remains much work to be done in the extension
of the research to higher pressures, and under conditions which obtain
in the operation of the steam-engine. The volumes and densities of
steam require further study, and the behavior of steam in the engine
is still but little known, otherwise than theoretically. Even the true
value of Joule's equivalent is not undisputed.
Some of the most recent experimental work bearing directly upon the
philosophy of the steam-engine is that of Hirn, whose determination of
the value of the mechanical equivalent was less than two per cent.
below that of Joule. Hirn tested by experiment, in 1853, and
repeatedly up to 1876, the analytical work of Rankine, which led to
the conclusion that steam doing work by expansion must become
gradually liquefied. Constructing a glass steam-engine cylinder, he
was enabled to see plainly the clouds of mist which were produced by
the expansion of steam behind the piston, where Regnault's experiments
prove that the steam should become drier and superheated, were no heat
transformed into mechanical energy. As will be seen hereafter, this
great discovery of Rankine is more important in its bearing upon the
theory of the steam-engine than any made during the century. Hirn's
confirmation stands, in value, beside the original discovery. In 1858
Hirn confirmed the work of Mayer and Joule by determining the work
done and the carbonic acid produced, as well as the increased
temperature due to their presence, where men were set at work in a
treadmill; he found the elevation of temperature to be much greater in
proportion to gas produced when the men were resting than when they
were at work. He thus proved conclusively the conversion of
heat-energy into mechanical work. It was from these experiments that
Helmholtz deduced the "modulus of efficiency" of the human machine at
one-fifth, and concluded that the heart works with eight times the
efficiency of a locomotive-engine, thus confirming a statement of
Rumford, who asserted the higher efficiency of the animal.
Hirn's most important experiments in this department were made upon
steam-engines of considerable size, including simple and compound
engines, and using steam sometimes saturated and sometimes superheated
to temperatures as high, on some occasions, as 340 deg. Cent. He
determined the work done, the quantity of heat entering, and the
amount rejected from, the steam-cylinder, and thus obtained a coarse
approximation to the value of the heat-equivalent. His figure varied
from 296 to 337 kilogrammetres. But, in all cases, the loss of heat
due to work done was marked, and, while these researches could not, in
the nature of the case, give accurate quantitative results, they are
of great value as qualitatively confirming Mayer and Joule, and
proving the transformation of energy.
Thus, as we have seen, experimental investigation and analytical
research have together created a new science, and the philosophy of
the steam-engine has at last been given a complete and well-defined
form, enabling the intelligent engineer to comprehend the operation of
the machine, to perceive the conditions of efficiency, and to look
forward in a well-settled direction for further advances in its
improvement and in the increase of its efficiency.
A very concise _resume_ of the principal facts and laws bearing upon
the philosophy of the steam-engine will form a fitting conclusion to
this historical sketch.
The term "energy" was first used by Dr. Young as the equivalent of the
work of a moving body, in his hardly yet obsolete "Lectures on Natural
Philosophy."
Energy is the capacity of a moving body to overcome resistance offered
to its motion; it is measured either by the product of the mean
resistance into the space through which it is overcome, or by the
half-product of the mass of the body into the square of its velocity.
Kinetic energy is the actual energy of a moving body; potential energy
is the measure of the work which a body is capable of doing under
certain conditions which, without expending energy, may be made to
affect it, as by the breaking of a cord by which a weight is
suspended, or by firing a mass of explosive material. The British
measure of energy is the foot-pound; the metric measure is the
kilogrammetre.
Energy, whether kinetic or potential, may be observable and due to
mass-motion; or it may be invisible and due to molecular movements.
The energy of a heavenly body or of a cannon-shot, and that of heat or
of electrical action, are illustrations of the two classes. In Nature
we find utilizable potential energy in fuel, in food, in any available
head of water, and in available chemical affinities. We find kinetic
energy in the motion of the winds and the flow of running water, in
the heat-motion of the sun's rays, in heat-currents on the earth, and
in many intermittent movements of bodies acted on by applied forces,
natural or artificial. The potential energy of fuel and of food has
already been seen to have been derived, at an earlier period, from the
kinetic energy of the sun's rays, the fuel or the food being thus made
a storehouse or reservoir of energy. It is also seen that the animal
system is simply a "mechanism of transmission" for energy, and does
not create but simply diverts it to any desired direction of
application.
All the available forms of energy can be readily traced back to a
common origin in the potential energy of a universe of nebulous
substance (chaos), consisting of infinitely diffused matter of
immeasurably slight density, whose "energy of position" had been,
since the creation, gradually going through a process of
transformation into the several forms of kinetic and potential energy
above specified, through intermediate methods of action which are
usually still in operation, such as the potential energy of chemical
affinity, and the kinetic forms of energy seen in solar radiation, the
rotation of the earth, and the heat of its interior.
The _measure_ of any given quantity of energy, whatever may be its
form, is the product of the resistance which it is capable of
overcoming into the space through which it can move against that
resistance, i. e., by the product RS. Or it is measured by the
equivalent expressions (MV^{2})/2, or WV^{2}/2_g_, in which W is
the weight, M is the "mass" of matter in motion, V the velocity, and
_g_ the dynamic measure of the force of gravity, 32-1/6 feet, or 9.8
metres, per second.
There are three great laws of energetics:
1. The sum total of the energy of the universe is invariable.
2. The several forms of energy are interconvertible, and possess an
exact quantitative equivalence.
3. The tendency of all forms of kinetic energy is continually toward
reduction to forms of molecular motion, and to their final dissipation
uniformly throughout space.
The history of the first two of these laws has already been traced.
The latter was first enunciated by Prof. Sir William Thomson in 1853.
Undissipated energy is called "Entrophy."
The science of thermo-dynamics is, as has been stated, a branch of the
science of energetics, and is the only branch of that science in the
domain of the physicist which has been very much studied. This branch
of science, which is restricted to the consideration of the relations
of heat-energy to mechanical energy, is based upon the great fact
determined by Rumford and Joule, and considers the behavior of those
fluids which are used in heat-engines as the media through which
energy is transferred from the one form to the other. As now accepted,
it assumes the correctness of the hypothesis of the dynamic theory of
fluids, which supposes their expansive force to be due to the motion
of their molecules.
This idea is as old as Lucretius, and was distinctly expressed by
Bernouilli, Le Sage and Prevost, and Herapath. Joule recalled
attention to this idea, in 1848, as explaining the pressure of gases
by the impact of their molecules upon the sides of the containing
vessels. Helmholtz, ten years later, beautifully developed the
mathematics of media composed of moving, frictionless particles, and
Clausius has carried on the work still further.
The general conception of a gas, as held to-day, including the
vortex-atom theory of Thomson and Rankine, supposes all bodies to
consist of small particles called molecules, each of which is a
chemical aggregation of its ultimate parts or atoms. These molecules
are in a state of continual agitation, which is known as heat-motion.
The higher the temperature, the more violent this agitation; the total
quantity of motion is measured as _vis viva_ by the half-product of
the mass into the square of the velocity of molecular movement, or in
heat-units by the same product divided by Joule's equivalent. In
solids, the range of motion is circumscribed, and change of form
cannot take place. In fluids, the motion of the molecules has become
sufficiently violent to enable them to break out of this range, and
their motion is then no longer definitely restricted.
The laws of thermo-dynamics are, according to Rankine:
1. Heat-energy and mechanical energy are mutually convertible, one
British thermal unit being the equivalent in heat-energy of 772
foot-pounds of mechanical energy, and one metric _calorie_ equal to
423.55 kilogrammetres of work.
2. The energy due to the heat of each of the several equal parts into
which a uniformly hot substance may be divided is the same; and the
total heat-energy of the mass is equal to the sum of the energies of
its parts.[113]
[113] This uniformity is not seen where a substance is changing its
physical state while developing its heat-energy, as occurs with
steam doing work while expanding.
It follows that the work performed by the transformation of the energy
of heat, during any indefinitely small variation of the state of a
substance as respects temperature, is measured by the product of the
absolute temperature into the variation of a "function," which
function is the rate of variation of the work so done with
temperature. This function is the quantity called by Rankine the
"heat-potential" of the substance for the given kind of work. A
similar function, which comprehends the total heat-variation,
including both heat transformed and heat needed to effect accompanying
physical changes, is called the "thermo-dynamic function." Rankine's
expression for the general equation of thermo-dynamics includes the
latter, and is given by him as follows:
J_dh_ = _d_H = _kd_[tau] + [tau]_d_F = [tau]_d_[phi],
in which J is Joule's equivalent, _dh_ the variation of total heat in
the substance, _kd_[tau] the product of the "dynamic specific heat"
into the variation of temperature, or the total heat demanded to
produce other changes than a transformation of energy, and [tau]_d_F
is the work done by the transformation of heat-energy, or the product
of the absolute temperature, [tau], into the differential of the
heat-potential. [phi] is the thermo-dynamic function, and
[tau]_d_[phi] measures the whole heat needed to produce,
simultaneously, a certain amount of work or of mechanical energy, and,
at the same time, to change the temperature of the working substance.
Studying the behavior of gases and vapors, it is found that the work
done when they are used, like steam, in heat-engines, consists of
three parts:
(_a._) The change effected in the total actual heat-motion of the
fluid.
(_b._) That heat which is expended in the production of internal work.
(_c._) That heat which is expended in doing the external work of
expansion.
In any case in which the total heat expended exceeds that due the
production of work on external bodies, the excess so supplied is so
much added to the intrinsic energy of the substance absorbing it.
The application of these laws to the working of steam in the engine is
a comparatively recent step in the philosophy of the steam-engine, and
we are indebted to Rankine for the first, and as yet only, extended
and in any respect complete treatise embodying these now accepted
principles.
It was fifteen years after the publication of the first logical theory
of the steam-engine, by Pambour,[114] before Rankine, in 1859, issued
the most valuable of all his works, "The Steam-Engine and other Prime
Movers." The work is far too abstruse for the general reader, and is
even difficult reading for many accomplished engineers. It is
excellent beyond praise, however, as a treatise on the thermo-dynamics
of heat-engines. It will be for his successors the work of years to
extend the application of the laws which he has worked out, and to
place the results of his labors before students in a readily
comprehended form.
[114] "Theorie de la Machine a Vapeur," par le Chevalier F. M. G. de
Pambour, Paris, 1844.
William J. Macquorn Rankine, the Scotch engineer and philosopher, will
always be remembered as the author of the modern philosophy of the
steam-engine, and as the greatest among the founders of the science of
thermo-dynamics. His death, while still occupying the chair of
engineering at the University of Glasgow, December 24, 1872, at the
early age of fifty-two, was one of the greatest losses to science and
to the profession which have occurred during the century.
CHAPTER VIII.
_THE PHILOSOPHY OF THE STEAM-ENGINE._
ITS APPLICATION; ITS TEACHINGS RESPECTING THE CONSTRUCTION OF THE
ENGINE AND ITS IMPROVEMENT.
"Oftentimes an Uncertaintie hindered our going on so merrily, but by
persevering the Difficultie was mastered, and the new Triumph gave
stronger Heart unto us."--RALEIGH.
"If everything which we cannot comprehend is to be called an
impossibility, how many are daily presented to our eyes! and in
contemning as false that which we consider to be impossible, may we
not be depreciating a giant's effort to give an importance to our
own weakness?"--MONTAIGNE.
"They who aim vigorously at perfection will come nearer to it than
those whose laziness or despondency makes them give up its pursuit
from the feeling of its being unattainable."--CHESTERFIELD.
As has been already stated, the steam-engine is a machine which is
especially designed to transform energy, originally dormant or
potential, into active and usefully available kinetic energy.
When, millions of years ago, in that early period which the geologists
call the carboniferous, the kinetic energy of the sun's rays, and of
the glowing interior of the earth, was expended in the decomposition
of the vast volumes of carbonic acid with which air was then charged,
and in the production of a life-sustaining atmosphere and of the
immense forests which then covered the earth with their almost
inconceivably luxuriant vegetation, there was stored up for the
benefit of the human race, then uncreated, an inconceivably great
treasure of potential energy, which we are now just beginning to
utilize. This potential energy becomes kinetic and available wherever
and whenever the powerful chemical affinity of oxygen for carbon is
permitted to come into play; and the fossil fuel stored in our
coal-beds or the wood of existing forests is, by the familiar process
of combustion, permitted to return to the state of combination with
oxygen in which it existed in the earliest geological periods.
The philosophy of the steam-engine, therefore, traces the changes
which occur from this first step, by which, in the furnace of the
steam-boiler, this potential energy which exists in the tendency of
carbon and oxygen to combine to form carbonic acid is taken advantage
of, and the utilizable kinetic energy of heat is produced in
equivalent amount, to the final application of resulting mechanical
energy to machinery of transmission, through which it is usefully
applied to the elevation of water, to the driving of mills and
machinery of all kinds, or to the hauling of "lightning" trains on our
railways, or to the propulsion of the Great Eastern.
The kinetic heat-energy developed in the furnace of the steam-boiler
is partly transmitted through the metallic walls which inclose the
steam and water within the boiler, there to evaporate water, and to
assume that form of energy which exists in steam confined under
pressure, and is partly carried away into the atmosphere in the
discharged gaseous products of combustion, serving, however, a useful
purpose, _en route_, by producing the draught needed to keep up
combustion.
The steam, with its store of heat-energy, passes through tortuous
pipes and passages to the steam-cylinder of the engine, losing more or
less heat on the way, and there expands, driving the piston before it,
and losing heat by the transformation of that form of energy while
doing mechanical work of equivalent amount. But this steam-cylinder is
made of metal, a material which is one of the best conductors of heat,
and therefore one of the very worst possible substances with which to
inclose anything as subtile and difficult of control as the heat
pervading a condensible vapor like steam. The process of internal
condensation and reevaporation, which is the great enemy of economical
working, thus has full play, and is only partly checked by the heat
from the steam-jacket, which, penetrating the cylinder, assists by
keeping up the temperature of the internal surface and checking the
first step, condensation, which is an essential preliminary to the
final waste by reevaporation. The piston, too, is of metal, and
affords a most excellent way of exit for the heat escaping to the
exhaust side.
Finally, all unutilized heat rejected from the steam-cylinder is
carried away from the machine, either by the water of condensation,
or, in the non-condensing engine, by the atmosphere into which it is
discharged.
Having traced the method of operation of the steam-engine, it is easy
to discover what principles are comprehended in its philosophy, to
learn what are known facts bearing upon its operation, and to
determine what are the directions in which improvement must take
place, what are the limits beyond which improvement cannot possibly be
carried, and, in some directions, to determine what is the proper
course to pursue in effecting improvements. The general direction of
change in the past, as well as at present, is easily seen, and it may
usually be assumed that there will be no immediate change of direction
in a course which has long been preserved, and which is well defined.
We may, therefore, form an idea of the probable direction in which to
look for improvement in the near future.
Reviewing the operations which go on in this machine during the
process of transformation of energy which has been outlined, and
studying it more in detail, we may deduce the principles which govern
its design and construction, guide us in its management, and determine
its efficiency.
In the furnace of the boiler, the quantity of heat developed in
available form is proportional to the amount of fuel burned. It is
available in proportion to the temperature attained by the products of
combustion; were this temperature no higher than that of the boiler,
the heat would all pass off unutilized. But the temperature produced
by a given quantity of heat, measured in heat-units, is greater as the
volume of gas heated is less. It follows that, at this point,
therefore, the fuel should be perfectly consumed with the least
possible air-supply, and the least possible abstraction of heat before
combustion is complete. High temperature of furnace, also, favors
complete combustion. We hence conclude that, in the steam-boiler
furnace, fuel should be burned completely in a chamber having
non-conducting walls, and with the smallest air-supply compatible with
thorough combustion; and, further, that the air should be free from
moisture, that greatest of all absorbents of heat, and that the
products of combustion should be removed from the furnace before
beginning to drain their heat into the boiler. A fire-brick furnace, a
large combustion-chamber with thorough intermixture of gases within
it, good fuel, and a restricted and carefully-distributed supply of
air, seem to be the conditions which meet these requisites best.
The heat generated by combustion traverses the walls which separate
the gases of the furnace from the steam and water confined within the
boiler, and is then taken up by those fluids, raising their
temperature from that of the entering "feed-water" to that due the
steam-pressure, and expanding the liquid into steam occupying a
greatly-increased volume, thus doing a certain amount of work, besides
increasing temperature. The extent to which heat may thus be usefully
withdrawn from the furnace-gases depends upon the conductivity of the
metallic wall, the rate at which the water will take heat from the
metal, and the difference of temperature on the two sides of the
metal. Extended "heating-surface," therefore, a metal of high
conducting power, and a maximum difference of temperature on the two
sides of the separating wall of metal, are the essential conditions of
economy here. The heating-surface is sometimes made of so great an
area that the temperature of the escaping gases is too low to give
good chimney-draught, and a "mechanical draught" is resorted to,
revolving "fan-blowers" being ordinarily used for its production. It
is most economical to adopt this method. The steam-boiler is generally
constructed of iron--sometimes, but rarely, of cast-iron, although
"steel," where not hard enough to harden or temper, is better in
consequence of its greater strength and homogeneousness of structure,
and its better conductivity. The maximum conductivity of flow of heat
for any given material is secured by so designing the boiler as to
secure rapid, steady, and complete circulation of the water within it.
The maximum rapidity of transfer throughout the whole area of
heating-surface is secured, usually, by taking the feed-water into the
boiler as nearly as possible at the point where the gases are
discharged into the chimney-flue, withdrawing the steam nearer the
point of maximum temperature of flues, and securing opposite
directions of flow for the gases on the one side and the water on the
other. Losses of heat from the boiler, by conduction and radiation to
surrounding bodies, are checked as far as possible by non-conducting
coverings.
The mechanical equivalent of the heat generated in the boiler is
easily calculated when the conditions of working are known. A pound of
pure carbon has been found to be capable of liberating by its perfect
combustion, resulting in the formation of carbonic acid, 14,500
British thermal units, equivalent to 14,500 x 772 = 11,194,000
foot-pounds of work, and, if burned in one hour, to 11194000/1980000 =
5.6 horse-power. In other words, with perfect utilization, but 10/56 =
0.177, or about one-sixth, of a pound of carbon would be needed per
hour for each horse-power of work done. But even good coal is not
nearly all carbon, and has but about nine-tenths this heat-producing
power, and it is usually rated as yielding about 10,000,000
foot-pounds of work per pound. The evaporative power of pure carbon
being rated at 15 pounds of water, that of good coal may be stated at
13-1/2. In metric measures, one gramme of good coal should evaporate
about 13-1/2 grammes of water from the boiling-point, producing the
equivalent of about 3,000,000 kilogrammetres of work from the 7,272
_calories_ of heat thus generated. A gramme of pure carbon generates
in its combustion 8,080 _calories_ of heat. Per hour and per
horse-power, 0.08, or less than one-twelfth, of a kilogram of carbon
burned per hour evolves heat-energy equal to one horse-power.
Of the coal burned in a steam-boiler, it rarely happens that more than
three-fourths is utilized in making steam; 7,500,000 foot-pounds
(1,036,898 kilogrammetres) is, therefore, as much energy as is usually
sent to the engine per pound of good coal burned in the steam-boiler.
The "efficiency" of a good steam-boiler is therefore usually not far
from 0.75 as a maximum. Rankine estimates this quantity for ordinary
boilers of good design and with chimney-draught at
0.92
E = ------------;
1 + 0.5(F/S)
in which F/S is the ratio of weight of fuel burned per square foot of
grate to the ratio of heating to grate surface; this is a formula of
fairly close approximation for general practice.
The steam in the engine first drives the piston some distance before
the induction or steam valve is closed, and it then expands, doing
work, and condensing in proportion to work done as the expansion
proceeds, until it is finally released by the opening of the exhaust
or eduction valve. Saturated steam is modified in its action by a
process which has already been described, condensing at the beginning
and reevaporating at the end of the stroke, thus carrying into the
condenser considerable quantities of heat which should have been
utilized in the development of power. Whether this operation takes
place in one cylinder or in several is only of importance in so far as
it modifies the losses due to conduction and radiation of heat, to
condensation and reevaporation of steam, and to the friction of the
machine. It has already been seen how these losses are modified by the
substitution of the compound for the single-cylinder engine.
The laws of thermo-dynamics teach, as has been stated, that the
proportion of the heat-energy contained in the steam or other working
fluid which may be transformed into mechanical energy is a fraction
(H_{1} - H_{2})/H_{1}, of the total, in which H_{1} and H_{2} are the
quantities of heat contained in the steam at the beginning and at the
end of its operation, measuring from the absolute zero of heat-motion.
In perfect gases,
H_{1} - H_{2} [tau]_{1} - [tau]_{2} T_{1} - T_{2}
------------- = --------------------- = --------------------
H_{1} [tau]_{1} T_{1} + 461.2 deg. Fahr.
but in imperfect gases, and especially in vapors which, like steam,
condense, or otherwise change their physical state, this equality may
still exist,
(H_{1} - H_{2})/H_{1} = ([tau]_{1} - [tau]_{2})/[tau]_{1};
and the fluid is equally efficient with the
perfect gas as a working substance in a heat-engine. In any case it is
seen that the efficiency is greatest when the whole of the heat is
received at the maximum and rejected at the minimum attainable
temperatures.
Assuming this expression strictly accurate, a hot-air engine working
from 413.6 deg. Fahr, or 874.8 deg. absolute temperature, down to 122 deg. Fahr,
or 583.2 deg. absolute, should have an efficiency of 0.263, transforming
that proportion of available heat into mechanical work. The engines
of the steamer Ericsson closely approached this figure, and gave a
horse-power for each 1.87 pound of coal burned per hour.
Steam expands in the steam-cylinder quite differently under different
circumstances. If no heat is either communicated to it or abstracted
from it, however, it expands in an hyperbolic curve, losing its
tension much more rapidly than when expanded without doing work, in
consequence both of its change of volume and its condensation. The
algebraic expression for this method of expansion is, according to
Rankine, PV^{1.111} = C, a constant, or, according to other
authorities, from PV^{1.135} = C to PV^{1.140} = C. The greater the
value of the exponent of V, the greater the efficiency of the fluid
between any two temperatures. The maximum value has been found to be
given where the steam is saturated, but perfectly dry, at the
commencement of its expansion. The loss due to condensation on the
cooled interior surface of the cylinder at the commencement of the
stroke and the subsequent reevaporation as expansion progresses is
least when the cylinder is kept hot by its steam-jacket and when least
time is given during the stroke for this transfer of heat between the
metal and the vapor.
It may be said that, all things considered, therefore, losses of heat
in the steam-cylinder are least when the steam enters dry, or
moderately superheated, where the interior surfaces are kept hottest
by the steam-jacket or by the hot-air jacket sometimes used, and where
piston-speed and velocity of rotation are highest.[115] The best of
compound engines, using steam of seventy-five pounds pressure and
condensing, usually require about two pounds of coal per
hour--20,000,000 foot-pounds of energy at the furnace--to develop a
horse-power, i. e., about ten times the heat-equivalent of the
mechanical work which they accomplish. Were the steam to expand like
the permanent gases, they would have a theoretical efficiency of about
one-quarter; actually, the efficiency is only one-tenth. The
steam-engine, therefore, utilizes about two-fifths the heat-energy
theoretically available with the best type of engine in general use.
By far the greater part, nearly all, in fact, of the nine-tenths
wasted is rejected in the exhaust steam, and can only be saved by some
such method as is hereafter to be suggested of retaining that heat and
returning it to the boiler.
[115] In some cases, as in the Allen engine, the speed of piston has
become very high, approaching 800((stroke)^{1/3}).
The mechanical power which has now been communicated to the mechanism
of the engine by the transfer of the kinetic energy of the hot steam
to the piston is finally usefully applied to whatever "mechanism of
transmission" forms the connection with the machinery driven by the
engine. In this transfer, there is some loss in the engine itself, by
friction. This is an extremely variable amount, and it can be made
very small by skillful design and good workmanship and management. It
may be taken at one-half pound per square inch of piston for good
engines of 100 horse-power and upward, but is often several pounds in
very small engines. It is least when the rubbing surfaces are of
different materials, but both of smooth, hard, close-grained metal,
well lubricated, and where advantage is taken of any arrangement of
parts which permits the equilibration of pressure, as on the
shaft-bearings of double and triple engines. The friction of a
steam-engine of large size and good design is usually between five and
seven per cent. of its total power. It increases rapidly as the size
of engine decreases.
Having now traced somewhat minutely the growth of the steam-engine
from the beginning of the Christian era to the present time, having
rapidly outlined the equally gradual, though intermittent, growth of
its philosophy, and having shown how the principles of science find
application in the operation of this wonderful machine, we are now
prepared to study the conditions which control the intelligent
designer, and to endeavor to learn what are the lessons taught us by
science and by experience in regard to the essential requisites of
efficient working of steam and economy in the consumption of fuel. We
may even venture to point out definitely the direction in which
improvement is now progressing as indicated by a study of these
requisites, and may be able to perceive the natural limits to such
progress, and possibly to conjecture what must be the character of
that change of type which only can take the engineer beyond the limit
set to his advance so long as he is confined to the construction of
the present type of engine.
First, we must consider the question: _What is the problem, stated
precisely and in its most general form, that engineers have been here
attempting to solve?_
After stating the problem, we will examine the record with a view to
determine what direction the path of improvement has taken hitherto,
to learn what are the conditions of efficiency which should govern the
construction of the modern steam-engine, and, so far as we may judge
the future by the past, by inference, to ascertain what appears to be
the proper course for the present and for the immediate future. Still
further, we will inquire, what are the conditions, physical and
intellectual, which best aid our progress in perfecting the
steam-engine.
This most important problem may be stated in its most general, yet
definite, form as follows:
_To construct a machine which shall, in the most perfect manner
possible, convert the kinetic energy of heat into mechanical power,
the heat being derived from the combustion of fuel, and steam being
the receiver and the conveyer of that heat._
The problem, as we have already seen, embodies two distinct and
equally important inquiries:
The first: What are the scientific principles involved in the problem
as stated?
The second: How shall a machine be constructed that shall most
efficiently embody, and accord with, not only those scientific
principles, but also all of those principles of engineering practice
that so vitally affect the economical value of every machine?
The one question is addressed to the man of science, the other to the
engineer. They can be satisfactorily answered, even so far as our
knowledge at present permits, after studying with care the scientific
principles involved in the theory of the steam-engine under the best
light that science can afford us, and by a careful study of the
various steps of improvement that have taken place and of accompanying
variations of structure, analyzing the effect of each change, and
tracing the reasons for them.
The theory of the steam-engine is too important and too extensive a
subject to be satisfactorily treated here in even the most concise
possible manner. I can only attempt a plain statement of the course
which seems to be pointed out by science as the proper one to pursue
in the endeavor to increase the economical efficiency of
steam-engines.
The teachings of science indicate that _success in economically
deriving mechanical power from the energy of heat-motion will, in all
cases, be the greater as we work between more widely separated limits
of temperature, and as we more perfectly provide against losses by
dissipation of heat in directions in which it is unavailable for the
production of power_.
Scientific research, as we have seen, has proved that, in all known
varieties of heat-engine, a large loss of effect is unavoidable from
the fact that we cannot, in the ordinary steam-engine, reduce the
lower limit of temperature, in working, below a point which is far
above the absolute zero of temperature--far above that point at which
bodies have no heat-motion. The point corresponding to the mean
temperature of the surface of the earth is above the ordinary lower
limit.
The higher the temperature of the steam when it enters the steam
cylinder, and the lower that which it reaches before the exhaust
occurs, the greater, science tells us, will be our success, provided
we at the same time avoid waste of heat and power.
Now, looking back over the history of the steam-engine, we may briefly
note the prominent improvements and the most striking changes of form,
and may thus endeavor to obtain some idea of the general direction in
which we are to look for further advance.
Beginning with the machine of Porta, at which point we may first take
up an unbroken thread, it will be remembered that we there found a
single vessel performing the functions of all the parts of a modern
pumping-engine; it was, at once, boiler, steam-cylinder, and
condenser, as well as both a lifting and a forcing pump.
The Marquis of Worcester divided the engine into two parts, using a
separate boiler.
Savery duplicated that part of the engine of Worcester which performed
the several parts of pump, steam-cylinder, and condenser, and added
the use of water to effect rapid condensation, perfecting, so far as
it was ever perfected, the steam-engine as a simple machine.
Newcomen and Calley next separated the pump from the steam-engine
proper, producing the modern steam-engine--the engine as a train of
mechanism; and in their engine, as in Savery's, we noticed the use of
surface condensation first, and subsequently that of the jet thrown
into the midst of the steam to be condensed.
Watt finally effected the crowning improvements, and completed the
movement oL "differentiation" by separating the condenser from the
steam-cylinder. Here this process of change ceased, the several
important operations of the steam-engine now being conducted each in a
separate vessel. The boiler furnished the steam, the cylinder derived
from it mechanical power, and it was finally condensed in a separate
vessel, while the power which had been obtained from it in the
steam-cylinder was transmitted through still other parts, to the
pumps, or wherever work was to be done.
Watt, also, took the initiative in another direction. He continually
increased the efficiency of the machine by improving the proportions
of its parts and the character of its workmanship, thus making it
possible to render available many of those improvements in detail upon
which effectiveness is so greatly dependent and which are only useful
when made by a skillful workman.
Watt and his contemporaries also commenced that movement toward higher
pressures of steam and greater expansion which has been the most
striking feature noticed in the progress of steam-engineering since
his time. Newcomen used steam of barely more than atmospheric pressure
and raised 105,000 pounds of water one foot high with a pound of coal
consumed. Smeaton raised the pressure somewhat and increased the duty
considerably. Watt started with a duty double that of Newcomen and
raised it to 320,000 foot-pounds per pound of coal, with steam at 10
pounds pressure. To-day, Cornish engines of the same general plan as
those of Watt, but worked with 40 to 60 pounds of steam and expanding
three or four times, do a duty probably averaging, with the better
class of engines, 600,000 foot-pounds per pound of coal. The compound
pumping-engine runs the figure up to above 1,000,000.
The increase in steam-pressure and in expansion since Watt's time has
been accompanied by a very great improvement in workmanship--a
consequence, very largely, of the rapid increase in perfection, and in
the wide range of adaptation of machine-tools--by higher skill and
intelligence in designing engines and boilers, by increased
piston-speed, greater care in obtaining dry steam, and in keeping it
dry until thrown out of the cylinder, either by steam-jacketing or by
superheating, or both combined; it has further been accompanied by a
greater attention to the important matter of providing carefully
against losses by radiation and conduction of heat. We use, finally,
the compound or double-cylinder engine for the purpose of saving some
of the heat usually lost in internal condensation and reevaporation,
and precipitation of condensed vapor from great expansion.
It is evident that, although there is a limit, tolerably well defined,
in the scale of temperature, below which we cannot expect to pass, a
degree gained in approaching this lower limit is more remunerative
than a degree gained in the range of temperature available by
increasing temperatures.[116]
[116] The fact here referred to is easily seen if it is supposed
that an engine is supplied with steam at a temperature of 400 deg.
above absolute zero and works it, without waste, down to a
temperature of 200 deg.. Suppose one inventor to adapt the engine to the
use of steam of a range from 500 deg. down to 200 deg., while another works
his engine, with equally effective provision against losses, between
the limits of 400 deg. and 100 deg., an equal range with a lower mean. The
first case gives an efficiency of one-half, the second three-fifths,
and the third three-fourths, the last giving the highest effect.
Hence the attempt made by the French inventor, Du Trembly, about the
year 1850, and by other inventors since, to utilize a larger
proportion of heat by approaching more closely the lower limit, was in
accordance with known scientific principles.
We may summarize the result of our examination of the growth of the
steam-engine thus:
_First._ The process of improvement has been one, primarily, of
"differentiation;"[117] the number of parts has been continually
increased; while the work of each part has been simplified, a separate
organ being appropriated to each process in the cycle of operations.
[117] This term, though perhaps not familiar to engineers, expresses
the idea perfectly.
_Secondly._ A kind of secondary process of differentiation has, to
some extent, followed the completion of the primary one, in which
secondary process one operation is conducted partly in one and partly
in another portion of the machine. This is illustrated by the two
cylinders of the compound engine and by the duplication noticed in the
binary engine.
_Thirdly._ The direction of improvement has been marked by a continual
increase of steam-pressure, greater expansion, provision for obtaining
dry steam, high piston-speed, careful protection against loss of heat
by conduction or radiation, and, in marine engines, by surface
condensation.
The direction which improvement seems now to be taking, and the proper
direction, as indicated by an examination of the principles of
science, as well as by our review of the steps already taken, would
seem to be: working between the widest attainable limits of
temperature.
Steam must enter the machine at the highest possible temperature, must
be protected from waste, and must retain, at the moment before
exhaust, the least possible amount of heat. He whose inventive genius,
or mechanical skill, contributes to effect either the use of higher
steam with safety and without waste, or the reduction of the
temperature of discharge, confers a boon upon mankind.
In detail: In the engine, the tendency is, and may probably be
expected to continue, in the near future at least, toward higher
steam-pressure, greater expansion in more than one cylinder,
steam-jacketing, superheating, a careful use of non-conducting
protectors against waste, and the adoption of still higher
piston-speeds.
In the boiler: more complete combustion without excess of air passing
through the furnace, and more thorough absorption of heat from the
furnace-gases. The latter will probably be ultimately effected by the
use of a mechanically produced draught, in place of the far more
wasteful method of obtaining it by the expenditure of heat in the
chimney.
In construction we may anticipate the use of better materials, and
more careful workmanship, especially in the boiler, and much
improvement in forms and proportions of details.
In management, there is a wide field for improvement, which
improvement we may feel assured will rapidly take place, as it has now
become well understood that great care, skill, and intelligence are
important essentials to the economical management of the steam-engine,
and that they repay, liberally, all of the expense in time and money
that is requisite to secure them.
In attempting improvements in the directions indicated, it would be
the height of folly to assume that we have reached a limit in any one
of them, or even that we have approached a limit. If further progress
seems checked by inadequate returns for efforts made, in any case, to
advance beyond present practice, it becomes the duty of the engineer
to detect the cause of such hinderance, and, having found it, to
remove it.
A few years ago, the movement toward the expansive working of high
steam was checked by experiments seeming to prove positive
disadvantage to follow advance beyond a certain point. A careful
revision of results, however, showed that this was true only with
engines built, as was then common, in utter disregard of all the
principles involved in such a use of steam, and of the precautions
necessary to be taken to insure the gain which science taught us
should follow. The hinderances are mechanical, and it is for the
engineer to remove them.
The last remark is especially applicable to the work of the engineer
who is attempting to advance in the direction in which, as already
intimated, an unmistakable revolution is now progressing, the
modification of the modern steam-engine to adapt it safely and
successfully to run at the high piston-speed, and great velocity of
rotation which have been already attained and which must undoubtedly
be greatly exceeded in the future. As there is no known and definite
limit to the economical increase of speed, and as the limit set by
practical conditions is continually being set farther back as the
builder acquires greater skill and attains greater accuracy of
workmanship and the power to insure greater rigidity of parts and
durability of wearing surfaces, we must anticipate a continued and
indefinite progress in this direction--a progress which must evidently
be of advantage, whatever may be the direction that other changes may
take.
It is evident that this adaptation of the steam-engine to great speed
of piston is the work now to be done by the engineer. The requisites
to success are obvious, and may be concisely stated as follows:
1. Extreme accuracy in proportions.
2. Perfect accuracy in fitting parts to each other.
3. Absolute symmetry of journals.
4. Ample area and maximum durability of rubbing surfaces.
5. Perfect certainty of an ample and continuous lubrication.
6. A nicely calculated and adjusted balance of reciprocating parts.
7. Security against injury by shock, whether due to the presence of
water in the cylinder or to looseness of running parts.
8. A "positive-motion" cut-off gear.
9. A powerful but sensitive and accurately-working governor
determining the degree of expansion.[118]
[118] The author is not absolutely confident on the latter point. It
may be found more economical and satisfactory, ultimately, to
determine the point of cut-off by an automatic apparatus adjusting
the expansion-gear _by reference to the steam-pressure_, regulating
the speed by attaching the governor elsewhere. The author has
devised several forms of apparatus of the kind referred to.
10. Well-balanced valves and an easy-working valve-gear.
11. Small volume of "dead-space," or "clearance," and properly
adjusted "compression."
It would seem sufficiently evident that the engine with detachable
("drop") cut-off valve-gear must, sooner or later, become an obsolete
type, although the substitution of springs or of steam-pressure for
gravity in the closing of the detached valve may defer greatly this
apparently inevitable change. The "engine of the future" will not
probably be a "drop cut-off engine."
As regards the construction of the engine as a piece of mechanism, the
principles and practice of good engineering are precisely the same,
whether applied in the designing of the compound or of the ordinary
type of steam-engine. The proportioning of the two machines to each
other in such manner as to form an effective whole, by procuring
approximately equal amounts of work from both, is the only essential
peculiarity of compound-engine design which calls for especial care,
and the method of securing success in practice may be stated to be,
for both forms of engines, as follows:
1. A good design, by which is meant--
_a._ Correct proportions, both in general dimensions and in
arrangement of parts, and proper forms and sizes of details to
withstand safely the forces which may be expected to come upon them.
_b._ A general plan which embodies the recognized practice of good
engineering.
_c._ Adaptation to the specific work which it is intended to perform,
in size and in efficiency. It sometimes happens that good practice
dictates the use of a comparatively uneconomical design.
2. Good construction, by which is meant--
_a._ The use of good material.
_b._ Accurate workmanship.
_c._ Skillful fitting and a proper "assemblage" of parts.
3. Proper connection with its work, that it may do that work under the
conditions assumed in its design.
4. Skillful management by those in whose hands it is placed.
_In general_, it may be stated that, to secure maximum economical
efficiency, steam should be worked at as high a pressure as possible,
and the expansion should be fixed as nearly as possible at the point
of maximum economy for that pressure. In general, the number of times
which the volume of steam may be expanded in the standard
single-cylinder, high-pressure engine with maximum economy, is not far
from 1/2 sqrt(P), where P is the pressure in pounds per square inch;
it rarely exceeds 0.75 sqrt(P). This may be exceeded in
double-cylinder engines. It is even more disadvantageous to cut off
too short than to "'follow' too far." With considerable expansion,
steam-jacketing and moderate superheating should be adopted, to
prevent excessive losses by internal condensation and reevaporation;
and expansion should take place in double cylinders, to avoid
excessive weight of parts, irregularity of motion, and great loss by
friction.
To secure this vitally important economy, it is advisable to seek some
practicable method of lining the cylinder with a non-conducting
material. This plan, as has been seen, was adopted by Smeaton, in
constructing Newcomen engines a century ago. Smeaton used wood on his
pistons, and Watt tried wood as a material for steam-cylinder linings.
That material is too perishable at temperatures now common, and no
metal has yet been substituted, or even discovered, which answers the
same purpose. The loss will also be reduced by increasing the speed of
rotation and velocity of piston. Where no effectual means can be found
of preventing contact of the steam with a good absorbent and conductor
of heat, it will be found best to sacrifice some of the efficiency due
to the change of state of the vapor, by superheating it and sending it
into the cylinder at a temperature considerably exceeding that of
saturation. With low steam and slowly-moving pistons, it is better to
pursue the latter course than to attempt to increase the efficiency of
the engine by greater expansion.
External surfaces should be carefully covered by non-conductors and
non-radiators, to prevent losses by conduction and radiation of heat.
It is especially necessary to reduce back-pressure and to obtain the
most perfect vacuum possible without overloading the air-pump, if it
is desired to obtain the maximum efficiency by expansion, and it then
becomes also very necessary to reduce losses by "dead-spaces" and by
badly-adjusted valves.
The piston-speed should be as great as can be sustained with safety.
Good engines should not require more than W = (200/sqrt(P)) where W =
the weight of steam per hour and per horse-power; the best practice
gives about W = (180/sqrt(P)) in large engines with dry steam, high
piston-speed, and good design, construction, and management.
The expansion-valve gear should be simple. The point of cut-off is
perhaps best determined by the governor. The valve should close
rapidly, but without shock, and should be balanced, or some other
device should be adopted to make it easy to move and free from
liability to cutting or rapid wear.
The governor should act promptly and powerfully, and should be free
from liability to oscillate, and to thus introduce irregularities
which are sometimes not less serious than those which the instrument
is intended to prevent.
Friction should be reduced as much as possible, and careful provision
should be made to economize lubricants as well as fuel.
The Principles of Steam-Boiler Construction are exceedingly simple;
and although attempts are almost daily made to obtain improved
results by varying the design and arrangement of heating-surface, the
best boilers of nearly all makers of acknowledged standing are
practically equal in merit, although of very diverse forms.
In making boilers, the effort of the engineer should evidently be:
1. To secure complete combustion of the fuel without permitting
dilution of the products of combustion by excess of air.
2. To secure as high temperature of furnace as possible.
3. To so arrange heating-surfaces that, without checking draught, the
available heat shall be most completely taken up and utilized.
4. To make the form of boiler such that it shall be constructed
without mechanical difficulty or excessive expense.
5. To give it such form that it shall be durable, under the action of
the hot gases and of the corroding elements of the atmosphere.
6. To make every part accessible for cleaning and repairs.
7. To make every part as nearly as possible uniform in strength, and
in liability to loss of strength by wear and tear, so that the boiler
when old shall not be rendered useless by local defects.
8. To adopt a reasonably high "factor of safety" in proportioning
parts.
9. To provide efficient safety-valves, steam-gauges, and other
appurtenances.
10. To secure intelligent and very careful management.
In securing complete combustion, the first of these desiderata, an
ample supply of air and its thorough intermixture with the combustible
elements of the fuel are essential; for the second--high temperature
of furnace--it is necessary that the air-supply shall not be in excess
of that absolutely needed to give complete combustion. The efficiency
of a furnace in making heat available is measured by
T - T'
E = -------;
T - _t_
in which E represents the ratio of heat utilized to the whole
calorific value of the fuel, T is the furnace-temperature, T' the
temperature of the chimney, and _t_ that of the external air. The
higher the furnace-temperature and the lower that of the chimney, the
greater the proportion of heat available. It is further evident that,
however perfect the combustion, no heat can be utilized if either the
temperature of the chimney approximates to that of the furnace, or if
the temperature of the furnace is reduced by dilution approximately to
that of the boiler. Concentration of heat in the furnace is secured,
in some cases, by special expedients, as by heating the entering air,
or as in the Siemens gas-furnace, heating both the combustible gases
and the supporter of combustion. Detached fire-brick furnaces have an
advantage over the "fire-boxes" of steam-boilers in their higher
temperature; surrounding the fire with non-conducting and highly
heated surfaces is an effective method of securing high
furnace-temperature.
In arranging heating-surface, the effort should be to impede the
draught as little as possible, and so to place them that the
circulation of water within the boiler should be free and rapid at
every part reached by the hot gases. The directions of circulation of
water on the one side and of gas on the other side of the sheet
should, whenever possible, be opposite. The cold water should enter
where the cooled gases leave, and the steam should be taken off
farthest from that point. The temperature of chimney-gases has thus
been reduced in practice to less than 300 deg. Fahr., and an efficiency
equal to 0.75 to 0.80 the theoretical has been attained.
The extent of heating-surface simply, in all of the best forms of
boiler, determines the efficiency, and in them the disposition of that
surface seldom affects it to any great extent. The area of
heating-surface may also be varied within very wide limits without
very greatly modifying efficiency. A ratio of 25 to 1 in flue and 30
to 1 in tubular boilers represents the relative area of heating and
grate surfaces as chosen in the practice of the best-known builders.
The material of the boiler should be tough and ductile iron, or,
better, a soft steel containing only sufficient carbon to insure
melting in the crucible or on the hearth of the melting-furnace, and
so little that no danger may exist of hardening and cracking under the
action of sudden and great changes of temperature.
Where iron is used, it is necessary to select a somewhat hard, but
homogeneous and tough, quality for the fire-box sheets or any part
exposed to flames.
The factor of safety is invariably too low in this country, and is
never too high in Europe. Foreign builders are more careful in this
matter than our makers in the United States. The boiler should be
built strong enough to bear a pressure at least six times the proposed
working-pressure; as the boiler grows weak with age, it should be
occasionally tested to a pressure far above the working-pressure,
which latter should be reduced gradually to keep within the bounds of
safety. In the United States, the factor of safety is seldom more than
four in the new boilers, frequently much less, and even this is
reduced practically to one and a third by the operation of our
inspection-laws.
The principles just enunciated are those generally, perhaps
universally, accepted principles which are stated in all text-books of
science and of steam-engineering, and are accepted by both engineers
and men of science.
These principles are correct, and the deductions which have been here
formulated are rigidly exact, as applied to all types of heat-engine
in use; and they lead us to the determination, in all cases, of the
"modulus" of efficiency of the engine, i. e., to the calculation of
the ratio of its actual efficiency to that efficiency which it would
have, were it absolutely free from loss of heat by conduction or
radiation, or other method of loss of heat or waste of power, by
friction of parts or by shock.
The best modern marine compound engines sometimes, as we have seen,
consume as little as two pounds of coal per horse-power and per hour;
but this is but about one-tenth the power derivable from the fuel,
were all its heat thoroughly utilized. This loss may be divided thus:
70 per cent. rejected in exhausted steam; 20 per cent. lost by
conduction and radiation and by faults of mechanism and design; and
only the 10 per cent. remaining is utilized. Thirty per cent. of the
heat generated in the furnace is usually lost in the chimney, and of
the remainder, which enters the engine, 20 per cent. at most is all
which we can hope to save any portion of by improvements effected in
our best existing type of steam-engine. It has already been shown how
the engineer can best proceed in attempting this economy.
The direction in which further improvement must take place in the
standard type of engine is plainly that which shall most efficiently
check losses by internal condensation and reevaporation by the
transfer of heat to and from the metal of the steam-cylinder. The
condensation of steam doing work is evidently not a disadvantage, but,
on the contrary, a decided advantage.
A new type of engine can, if at all, probably only supersede the
common form when engineers can employ steam of very high pressure, and
adopt much greater range of expansion than is now usual. Great
velocity of piston and high speed of rotation are also essential in
the attempt to make any revolution in steam-engine construction a
success.
When a new form of steam-engine is likely to be introduced, if at all,
can be scarcely even conjectured. It seems evident that its success is
to be secured, if a revolution is ever to occur, by the adoption of
high steam-pressures, of great piston speeds, by care and skill in
design, by the use of exceptionally excellent materials of
construction, by great perfection of workmanship, and by intelligence
in its management.
Experiment and experience will probably lead gradually to the general
and safe employment of much higher steam-pressures and very greatly
increased piston-speeds, and may ultimately reveal and remove all
those difficulties which must invariably be expected to be met here,
as in all other attempts to effect radical changes, however important
they may be.
[Illustration]
* * * * *
_Scientific Publications._
=THE HUMAN SPECIES.= By A. DE QUATREFAGES, Professor of Anthropology
in the Museum of Natural History, Paris. 12mo, cloth, $2.00.
The work treats of the unity, origin, antiquity, and original
localization of the human species, peopling of the globe,
acclimatization, primitive man, formation of the human races, fossil
human races, present human races, and the physical and psychological
characters of mankind.
=STUDENTS' TEXT-BOOK OF COLOR; or, MODERN CHROMATICS.= With
Applications to Art and Industry. With 130 Original Illustrations, and
Frontispiece in Colors. By OGDEN N. ROOD, Professor of Physics in
Columbia College. 12mo, cloth, $2.00.
"In this interesting book Professor Rood, who, as a distinguished
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work is to be attributed to the fact that he is himself an
accomplished artist as well as an authoritative expounder of
science."--_Edinburgh Review, October, 1879, in an article on "The
Philosophy of Color._"
=EDUCATION AS A SCIENCE.= By ALEXANDER BAIN, LL. D. 12mo, cloth,
$1.75.
"This work must be pronounced the most remarkable discussion of
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hesitate to bespeak for it the widest circulation and the most
earnest attention. It should be in the hands of every school-teacher
and friend of education throughout the land."--_New York Sun._
=A HISTORY OF THE GROWTH OF THE STEAM-ENGINE.= By ROBERT H. THURSTON,
A. M., C. E., Professor of Mechanical Engineering in the Stevens
Institute of Technology, Hoboken, N. J., etc. With 163 Illustrations,
including 15 Portraits. 12mo, cloth, $2.50.
"Professor Thurston almost exhausts his subject; details of
mechanism are followed by interesting biographies of the more
important inventors. If, as is contended, the steam-engine is the
most important physical agent in civilizing the world, its history
is a desideratum, and the readers of the present work will agree
that it could have a no more amusing and intelligent historian than
our author."--_Boston Gazette._
=STUDIES IN SPECTRUM ANALYSIS.= By J. NORMAN LOCKYER, F. R. S.,
Correspondent of the Institute of France, etc. With 60 Illustrations.
12mo, cloth, $2.50.
"The study of spectrum analysis is one fraught with a peculiar
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interest in the matter before him, nor putting down the book until
the last page is reached."--_New York Evening Express._
=GENERAL PHYSIOLOGY OF MUSCLES AND NERVES.= By Dr. I. ROSENTHAL,
Professor of Physiology at the University of Erlangen. With
seventy-five Woodcuts. ("International Scientific Series.") 12mo,
cloth, $1.50.
"The attempt at a connected account of the general physiology of
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general data for this branch of science have been gained only within
the past thirty years."--_Extract from Preface._
=SIGHT=: An Exposition of the Principles of Monocular and Binocular
Vision By JOSEPH LE CONTE, LL. D., author of "Elements of Geology";
"Religion and Science"; and Professor of Geology and Natural History
in the University of California. With numerous Illustrations. 12mo,
cloth, $1.50.
"It is pleasant to find an American book which can rank with the
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=ANIMAL LIFE=, as affected by the Natural Conditions of Existence. By
KARL SEMPER, Professor of the University of Wuerzburg. With 2 Maps and
106 Woodcuts, and Index. 12mo, cloth, $2.00.
"This is in many respects one of the most interesting contributions
to zooelogical literature which has appeared for some
time."--_Nature._
=THE ATOMIC THEORY.= By AD. WURTZ, Membre de l'Institut; Doyen
Honoraire de la Faculte de Medecine; Professeur a la Faculte des
Sciences de Paris. Translated by E. CLEMINSHAW, M. A., F. C. S., F. I.
C., Assistant Master at Sherborne School. 12mo, cloth, $1.50.
"There was need for a book like this, which discusses the atomic
theory both in its historic evolution and in its present form. And
perhaps no man of this age could have been selected so able to
perform the task in a masterly way as the illustrious French
chemist, Adolph Wurtz. It is impossible to convey to the reader, in
a notice like this, any adequate idea of the scope, lucid
instructiveness, and scientific interest of Professor Wurtz's book.
The modern problems of chemistry, which are commonly so obscure from
imperfect exposition, are here made wonderfully clear and
attractive."--_The Popular Science Monthly._
=THE CRAYFISH.= An Introduction to the Study of Zooelogy. By Professor
T. H. HUXLEY, F. R. S. With 82 Illustrations. 12mo, cloth, $1.75.
"Whoever will follow these pages, crayfish in hand, and will try to
verify for himself the statements which they contain, will find
himself brought face to face, with all the great zooelogical
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"The reader of this valuable monograph will lay it down with a
feeling of wonder at the amount and variety of matter which has been
got out of so seemingly slight and unpretending a
subject."--_Saturday Review._
=SUICIDE=: An Essay In Comparative Moral Statistics. By HENRY
MORSELLI, Professor of Psychological Medicine in Royal University,
Turin. 12mo, Cloth, $1.75.
"Suicide" is a scientific inquiry, on the basis of the statistical
method, into the laws of suicidal phenomena. Dealing with the
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suicide in different countries, and the comparison of nations,
races, and periods in its manifestation. The influences of age, sex,
constitution, climate, season, occupation, religion, prevailing
ideas, the elements of character, and the tendencies of
civilization, are comprehensively analyzed in their bearing upon the
propensity to self-destruction. Professor Morselli is an eminent
European authority on this subject. It is accompanied by colored
maps illustrating pictorially the results of statistical inquiries.
=VOLCANOES: What they Are and what they Teach.= By J. W. JUDD,
Professor of Geology in the Royal School of Mines (London). With
Ninety-six Illustrations. 12mo. Cloth, $2.00.
"In no field has modern research been more fruitful than in that of
which Professor Judd gives a popular account in the present volume.
The great lines of dynamical, geological, and meteorological inquiry
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earth, and the vast influence of subterranean agencies.... His book
is very far from being a mere dry description of volcanoes and their
eruptions; it is rather a presentation of the terrestrial facts and
laws with which volcanic phenomena are associated."--_Popular
Science Monthly._
"The volume before us is one of the pleasantest science manuals we
have read for some time."--_Athenaeum._
"Mr. Judd's summary is so full and so concise that it is almost
impossible to give a fair idea in a short review."--_Pall Mall
Gazette._
=THE SUN.= By C. A. YOUNG, Ph. D., LL. D., Professor of Astronomy in
the College of New Jersey. With numerous Illustrations. 12mo. Cloth,
$2.00.
"Professor Young is an authority on 'The Sun,' and writes from
intimate knowledge. He has studied that great luminary all his life,
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to watch it, and has contributed important discoveries that have
extended our knowledge of it.
"It would take a cyclopaedia to represent all that has been done
toward clearing up the solar mysteries. Professor Young has
summarized the information, and presented it in a form completely
available for general readers. There is no rhetoric in his book; he
trusts the grandeur of his theme to kindle interest and impress the
feelings. His statements are plain, direct, clear, and condensed,
though ample enough for his purpose, and the substance of what is
generally wanted will be found accurately given in his
pages."--_Popular Science Monthly._
=ILLUSIONS: A Psychological Study.= By JAMES SULLY, author of
"Sensation and Intuition," etc. 12mo. Cloth. $1.50.
This volume takes a wide survey of the field of error, embracing in
its view not only the illusions commonly regarded as of the nature
of mental aberrations or hallucinations, but also other illusions
arising from that capacity for error which belongs essentially to
rational human nature. The author has endeavored to keep to a
strictly scientific treatment--that is to say, the description and
classification of acknowledged errors, and the exposition of them by
a reference to their psychical and physical conditions.
"This is not a technical work, but one of wide popular interest, in
the principles and results of which every one is concerned. The
illusions of perception of the senses and of dreams are first
considered, and then the author passes to the illusions of
introspection, errors of insight, illusions of memory, and illusions
of belief. The work is a noteworthy contribution to the original
progress of thought, and may be relied upon as representing the
present state of knowledge on the important subject to which it is
devoted."--_Popular Science Monthly._
=THE BRAIN AND ITS FUNCTIONS.= By J. LUYS, Physician to the Hospice de
la Salpetriere. With Illustrations. 12mo. Cloth, $1.50.
"No living physiologist is better entitled to speak with authority
upon the structure and functions of the brain than Dr. Luys. His
studies on the anatomy of the nervous system are acknowledged to be
the fullest and most systematic ever undertaken. Dr. Luys supports
his conclusions not only by his own anatomical researches, but also
by many functional observations of various other physiologists,
including of course Professor Ferrier's now classical
experiments."--_St. James's Gazette._
"Dr. Luys, at the head of the great French Insane Asylum, is one of
the most eminent and successful investigators of cerebral science
now living; and he has given unquestionably the clearest and most
interesting brief account yet made of the structure and operations
of the brain. We have been fascinated by this volume more than by
any other treatise we have yet seen on the machinery of sensibility
and thought; and we have been instructed not only by much that is
new, but by many sagacious practical hints such as it is well for
everybody to understand."--_The Popular Science Monthly._
=THE CONCEPTS AND THEORIES OF MODERN PHYSICS.= By J. B. STALLO. 12mo.
Cloth, $1.75.
"Judge Stallo's work is an inquiry into the validity of those
mechanical conceptions of the universe which are now held as
fundamental in physical science. He takes up the leading modern
doctrines which are based upon this mechanical conception, such as
the atomic constitution of matter, the kinetic theory of gases, the
conservation of energy, the nebular hypothesis, and other views, to
find how much stands upon solid empirical ground, and how much rests
upon metaphysical speculation. Since the appearance of Dr. Draper's
'Religion and Science,' no book has been published in the country
calculated to make so deep an impression on thoughtful and educated
readers as this volume.... The range and minuteness of the author's
learning, the acuteness of his reasoning, and the singular precision
and clearness of his style, are qualities which very seldom have
been jointly exhibited in a scientific treatise."--_New York Sun._
=THE FORMATION OF VEGETABLE MOULD, THROUGH THE ACTION OF WORMS, WITH
OBSERVATIONS ON THEIR HABITS.= By CHARLES DARWIN, LL. D., F. R. S.,
author of "On the Origin of Species," etc., etc. With Illustrations.
12mo, cloth. Price, $1.50.
"Mr. Darwin's little volume on the habits and instincts of
earth-worms is no less marked than the earlier or more elaborate
efforts of his genius by freshness of observation, unfailing power
of interpreting and correlating facts, and logical vigor in
generalizing upon them. The main purpose of the work is to point out
the share which worms have taken in the formation of the layer of
vegetable mould which covers the whole surface of the land in every
moderately humid country. All lovers of nature will unite in
thanking Mr. Darwin for the new and interesting light he has thrown
upon a subject so long overlooked, yet so full of interest and
instruction, as the structure and the labors of the
earth-worm."--_Saturday Review._
"Respecting worms as among the most useful portions of animate
nature, Dr. Darwin relates, in this remarkable book, their structure
and habits, the part they have played in the burial of ancient
buildings and the denudation of the land, in the disintegration of
rocks, the preparation of soil for the growth of plants, and in the
natural history of the world."--_Boston Advertiser._
=ANTS, BEES, AND WASPS.= A Record of Observations on the Habits of the
Social Hymenoptera. By Sir JOHN LUBBOCK, Bart., M. P., F. R. S., etc.,
author of "Origin of Civilization, and the Primitive Condition of
Man," etc., etc. With Colored Plates. 12mo, cloth, $2.00.
"This volume contains the record of various experiments made with
ants, bees, and wasps during the last ten years, with a view to test
their mental condition and powers of sense. The principal point in
which Sir John's mode of experiment differs from those of Huber,
Forel, McCook, and others, is that he has carefully watched and
marked particular insects, and has had their nests under observation
for long periods--one of his ants' nests having been under constant
inspection ever since 1874. His observations are made principally
upon ants because they show more power and flexibility of mind; and
the value of his studies is that they belong to the department of
original research."
"We have no hesitation in saying that the author has presented us
with the most valuable series of observations on a special subject
that has ever been produced, charmingly written, full of logical
deductions, and, when we consider his multitudinous engagements, a
remarkable illustration of economy of time. As a contribution to
insect psychology, it will be long before this book finds a
parallel."--_London Athenaeum._
=DISEASES OF MEMORY=: An Essay in the Positive Psychology. By TH.
RIBOT, author of "Heredity," etc. Translated from the French by
William Huntington Smith. 12mo, cloth, $1.50.
"M. Ribot reduces diseases of memory to law, and his treatise is of
extraordinary interest."--_Philadelphia Press._
"Not merely to scientific, but to all thinking men, this volume will
prove intensely interesting."--_New York Observer._
"M. Ribot has bestowed the most painstaking attention upon his
theme, and numerous examples of the conditions considered greatly
increase the value and interest of the volume."--_Philadelphia North
American._
"To the general reader the work is made entertaining by many
illustrations connected with such names as Linnaeus, Newton, Sir
Walter Scott, Horace Vernet, Gustave Dore, and many
others."--_Harrisburg Telegraph._
"The whole subject is presented with a Frenchman's vivacity of
style."--_Providence Journal._
"It is not too much to say that in no single work have so many
curious cases been brought together and interpreted in a scientific
manner."--_Boston Evening Traveller._
=MYTH AND SCIENCE.= By TITO VIGNOLI. 12mo, cloth, price, $1.50.
"His book is ingenious; ... his theory of how science gradually
differentiated from and conquered myth is extremely well wrought
out, and is probably in essentials correct."--_Saturday Review._
"The book is a strong one, and far more interesting to the general
reader than its title would indicate. The learning, the acuteness,
the strong reasoning power, and the scientific spirit of the author,
command admiration."--_New York Christian Advocate._
"An attempt made, with much ability and no small measure of success,
to trace the origin and development of the myth. The author has
pursued his inquiry with much patience and ingenuity, and has
produced a very readable and luminous treatise."--_Philadelphia
North American._
"It is a curious if not startling contribution both to psychology
and to the early history of man's development."--_New York World._
=MAN BEFORE METALS.= By N. JOLY, Professor at the Science Faculty of
Toulouse; Correspondent of the Institute. With 148 Illustrations,
12mo. Cloth, $1.75.
"The discussion of man's origin and early history, by Professor De
Quatrefages, formed one of the most useful volumes in the
'International Scientific Series,' and the same collection is now
further enriched by a popular treatise on paleontology, by M. N.
Joly, Professor in the University of Toulouse. The title of the
book, 'Man before Metals,' indicates the limitations of the writer's
theme. His object is to bring together the numerous proofs,
collected by modern research, of the great age of the human race,
and to show us what man was, in respect of customs, industries, and
moral or religious ideas, before the use of metals was known to
him."--_New York Sun._
"An interesting, not to say fascinating volume."--_New York
Churchman._
=ANIMAL INTELLIGENCE.= By GEORGE J. ROMANES, F. R. S., Zooelogical
Secretary of the Linnaean Society, etc. 12mo. Cloth, $1.75.
"My object in the work as a whole is twofold: First, I have thought
it desirable that there should be something resembling a text-book
of the facts of Comparative Psychology, to which men of science, and
also metaphysicians, may turn whenever they have occasion to
acquaint themselves with the particular level of intelligence to
which this or that species of animal attains. My second and much
more important object is that of considering the facts of animal
intelligence in their relation to the theory of descent."--_From the
Preface._
"Unless we are greatly mistaken, Mr. Romanes's work will take its
place as one of the most attractive volumes of the 'International
Scientific Series.' Some persons may, indeed, be disposed to say
that it is too attractive, that it feeds the popular taste for the
curious and marvelous without supplying any commensurate discipline
in exact scientific reflection; but the author has, we think, fully
justified himself in his modest preface. The result is the
appearance of a collection of facts which will be a real boon to the
student of Comparative Psychology for this is the first attempt to
present systematically well-assured observations on the mental life
of animals."--_Saturday Review._
"The author believes himself, not without ample cause, to have
completely bridged the supposed gap between instinct and reason by
the authentic proofs here marshaled of remarkable intelligence in
some of the higher animals. It is the seemingly conclusive evidence
of reasoning; powers furnished by the adaptation of means to ends in
cases which can not be explained on the theory of inherited aptitude
or habit."--_New York Sun._
=THE SCIENCE OF POLITICS.= By SHELDON AMOS, M. A., author of "The
Science of Law," etc. 12mo. Cloth, $1.75.
"To the political student and the practical statesman it ought to be
of great value."--_New York Herald._
"The author traces the subject from Plato and Aristotle in Greece,
and Cicero in Rome, to the modern schools in the English field, not
slighting the teachings of the American Revolution or the lessons of
the French Revolution of 1793. Forms of government, political terms,
the relation of law, written and unwritten, to the subject, a
codification from Justinian to Napoleon in France and Field in
America, are treated as parts of the subject in hand. Necessarily
the subjects of executive and legislative authority, police, liquor,
and land laws are considered, and the question ever growing in
importance in all countries, the relations of corporations to the
state."--_New York Observer._
=THE FUNDAMENTAL CONCEPTS OF MODERN PHILOSOPHIC THOUGHT, CRITICALLY
AND HISTORICALLY CONSIDERED.= By RUDOLPH EUCKEN, Ph. D., Professor in
Jena. With an Introduction by NOAH PORTER, President of Yale College.
One vol., 12mo, 304 pages. Cloth. Price, $1.75.
President Porter declares of this work that "there are few books
within his knowledge which are better fitted to aid the student who
wishes to acquaint himself with the course of modern speculation and
scientific thinking, and to form an intelligent estimate of most of
the current theories."
=MIND IN THE LOWER ANIMALS IN HEALTH AND DISEASE.= By W. LAUDER
LINDSAY, M. D., F. R. S. E., etc. 2 vols., 8vo. Cloth, $4.00.
"The author of this work, which, regarded merely as an accumulation
of verified and classified facts, is a unique and precious
contribution to the data of comparative psychology, claims that he
entered on his inquiry without any theory to defend, support, or
illustrate. We are bound to say that, while his general conclusions
are boldly and continually avowed, his claim of fairness and caution
is justified by his method of examining particular phenomena; that
he seems willing at all times to renounce any impression or belief
which is shown to be scientifically untenable."--_New York Sun._
"In this work--two volumes of over 500 pages--Dr. Lindsay marshals a
proportionately large number of facts against those philosophers who
maintain that the intelligence of man differs in kind and not simply
in degree from that of the lower animals. It is one purpose of his
book to show that the main differences between man and the lower
animals exist rather in their physical than in their mental
structure. In this way of thinking, all animals possess not the
semblance of, but the true substance of mind and will."--_New York
World._
"So far as we are aware there has been no treatise upon the subject
of animal intelligence so broad in its foundations, so well
considered, or so scientific in its methods of inquiry, as that
which has been prepared by Dr. W. Lauder Lindsay in two large
volumes, the first being devoted to a study of animal mind in
health, and the second to animal mind in disease. We may safely say
that his work is, in some respects, the most important essay of the
kind that has yet been undertaken. His observations have been
supplemented by a thorough mastery of the history and literature of
the subject, and hence his conclusions rest upon the broadest
possible foundation of safe induction. There is a good analytical
index to the book, as there ought to be to every work of the
kind."--_New York Evening Post._
=THE ELEMENTARY PRINCIPLES OF SCIENTIFIC AGRICULTURE.= By N. T.
LUPTON, LL. D., Professor of Chemistry in Vanderbilt University,
Nashville, Tenn. 18mo. Cloth. Price, 45 cents.
=A GLOSSARY OF BIOLOGICAL, ANATOMICAL, AND PHYSIOLOGICAL TERMS.= By
THOMAS DUNMAN. Small 8vo. Cloth. 161 pages. Price, $1.00.
"It has been the author's task to furnish here a small and
convenient but very complete glossary of those terms; and he has
done this so well, both in his choice of terms for definition and in
his clear exposition of their etymological and technical meaning, as
to leave nothing to be desired in this direction."--_New York
Evening Post._
_For sale by all booksellers, or any work sent by mail, post-paid,
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D. APPLETON & CO., Publishers,
1, 3, & 5 Bond Street, New York.
SCIENTIFIC LECTURES AND ESSAYS.
=Popular Lectures on Scientific Subjects.= By H. HELMHOLTZ, Professor
of Physics in the University of Berlin. First Series. Translated by E.
ATKINSON, Ph. D., F. C. S. With an Introduction by Professor TYNDALL.
With 51 Illustrations. 12mo. Cloth, $2.00.
_CONTENTS._--On the Relation of Natural Science to Science in
General.--On Goethe's Scientific Researches.--On the Physiological
Causes of Harmony in Music--Ice and Glaciers.--Interaction of the
Natural Forces.--The Recent Progress of the Theory of Vision.--The
Conservation of Force.--Aim and Progress of Physical Science.
=Popular Lectures on Scientific Subjects.= By H. HELMHOLTZ. Second
Series. 12mo. Cloth, $1.50.
_CONTENTS._--Gustav Magnus.--In Memoriam.--The Origin and
Significance of Geometrical Axioms.--Relation of Optics to
Painting.--Origin of the Planetary System.--On Thought in
Medicine.--Academic Freedom in German Universities.
"Professor Helmholtz's second series of 'Popular Lectures on
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He who anticipates a dry record of facts or a sequence of immature
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method these discourses are models of excellence, and, since they
come from a man whose learning and authority are beyond dispute,
they may be accepted as presenting the conclusions of the best
thought of the times in scientific fields."--_Boston Traveler._
=Science and Culture, and other Essays.= By Professor T. H. HUXLEY, F.
R. S. 12mo. Cloth, $1.50.
"Of the essays that have been collected by Professor Huxley in this
volume, the first four deal with some aspect of education. Most of
the remainder are expositions of the results of biological research,
and, at the same time, illustrations of the history of scientific
ideas. Some of these are among the most interesting of Professor
Huxley's contributions to the literature of science."--_London
Academy._
"It is refreshing to be brought into converse with one of the most
vigorous and acute thinkers of our time, who has the power of
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Spectator._
=Scientific Culture, and other Essays.= By JOSIAH PARSONS COOKE,
Professor of Chemistry and Mineralogy in Harvard College. 12mo. Cloth,
$1.00.
These essays are an outcome of a somewhat large experience in
teaching physical science to college students. Cambridge,
Massachusetts, early set the example of making the student's own
observations in the laboratory or cabinet the basis of all teaching,
either in experimental or natural history science; and this example
has been generally followed. "But in most centers of education,"
writes Professor Cooke, "the old traditions so far survive that the
great end of scientific culture is lost in attempting to conform
even laboratory instruction to the old academic methods of
recitations and examinations. To point out this error, and to claim
for science-teaching its appropriate methods, was one object of
writing these essays."
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