The transformation which takes place in the furnace is a chemical change; the transfer of heat to the water and the subsequent phenomena accompanying its pa.s.sage through the engine are physical changes, some of which require for their investigation abstruse mathematical operations. A thorough comprehension of the principles governing the operation of the steam-engine, therefore, can only be attained after studying the phenomena of physical science with sufficient minuteness and accuracy to be able to express with precision the laws of which those sciences are const.i.tuted. The study of the philosophy of the steam-engine involves the study of chemistry and physics, and of the new science of energetics, of which the now well-grown science of thermo-dynamics is a branch. This sketch of the growth of the steam-engine may, therefore, be very properly concluded by an outline of the growth of the several sciences which together make up its philosophy, and especially of the science of thermo-dynamics, which is peculiarly the science of the steam-engine and of the other heat-engines.
These sciences, like the steam-engine itself, have an origin which antedates the commencement of the Christian era; but they grew with an almost imperceptible growth for many centuries, and finally, only a century ago, started onward suddenly and rapidly, and their progress has never since been checked. They are now fully-developed and well-established systems of natural philosophy. Yet, like that of the steam-engine and of its companion heat-engines, their growth has by no means ceased; and, while the student of science cannot do more than indicate the direction of their progress, he can readily believe that the beginning of the end is not yet reached in their movement toward completeness, either in the determination of facts or in the codification of their laws.
When Hero lived at Alexandria, the great "Museum" was a most important centre, about which gathered the teachers of all then known philosophies and of all the then recognized but unformed sciences, as well as of all those technical branches of study which had already been so far developed as to be capable of being systematically taught.
Astronomical observations had been made regularly and uninterruptedly by the Chaldean astrologers for two thousand years, and records extending back many centuries had been secured at Babylon by Calisthenes and given to Aristotle, the father of our modern scientific method. Ptolemy had found ready to his hand the records of Chaldean observers of eclipses extending back nearly 650 years, and marvelously accurate.[103]
[103] Their estimate of the length of the Saros, or cycle of eclipses--over 19 years--was "within 19-1/2 minutes of the truth."--DRAPER.
A rude method of printing with an engraved roller on plastic clay, afterward baked, thus making up ceramic libraries, was practised long previous to this time; and in the alcoves in which Hero worked were many of these books of clay.
This great Library and Museum of Alexandria was founded three centuries before the birth of Christ, by Ptolemy Soter, who established as his capital that great Egyptian city when the death of his brother, the youthful but famous conqueror whose name he gave it, placed him upon the throne of the colossal successor of the then fallen Persian Empire. The city itself, embellished with every ornament and provided with every luxury that the wealth of a conquered world or the skill, taste, and ingenuity of the Greek painters, sculptors, architects, and engineers could provide, was full of wonders; it was a wonder in itself. This rich, populous, and magnificent city was the metropolis of the then civilized world.
Trade, commerce, manufactures, and the fine arts were all represented in this splendid exchange, and learning found its most acceptable home and n.o.blest field within the walls of Ptolemy"s Museum; its disciples found themselves welcomed and protected by its founder and his successors, Philadelphus and the later Ptolemies.
The Alexandrian Museum was founded with the declared object of collecting all written works of authority, of promoting the study of literature and art, and of stimulating and a.s.sisting experimental and mathematical scientific investigation and research. The founders of modern libraries, colleges, and technical schools have their prototype in intelligence, public spirit, and liberality, in the first of the Ptolemies, who not only spent an immense sum in establishing this great inst.i.tution, but spared no expense in sustaining it. Agents were sent out into all parts of the world, purchasing books. A large staff of scribes was maintained at the museum, whose duty it was to multiply copies of valuable works, and to copy for the library such works as could not be purchased.
The faculty of the museum was as carefully organized as was the plan of its administration. The four princ.i.p.al faculties of astronomy, literature, mathematics, and medicine were subdivided into sections devoted to the several branches of each department. The collections of the museum were as complete as the teachers of the undeveloped sciences of the time could make them. Lectures were given in all branches of study, and the number of students was sometimes as great as twelve or thirteen thousand. The number of books which were collected here, when the barbarian leaders of the Roman troops under Caesar burned the greater part of it, was stated to be 700,000. Of these, 400,000 were within the museum itself, and were all destroyed; the rest were in the temple of Serapis, and, for the time, escaped destruction.
The greatest of all the great men who lived at Alexandria at the time of the establishment of the museum was Aristotle, the teacher of Alexander and the friend of Ptolemy. It is to Aristotle that we owe the systematization of the philosophical ideas of Plato and the creation of the inductive method, in which has originated all modern science. It is to the learned men of Alexandria that we are indebted for so effective an application of the Aristotelian philosophy that all the then known sciences were given form, and were so thoroughly established that the work of modern science has been purely one of development.
The inductive method, which built up all the older sciences, and which has created all those of recent development, consists, first, in the discovery and quant.i.tative determination of facts; secondly, when a sufficient number of facts have been thus observed and defined, in the grouping of those facts, and the detection, by a study of their mutual relations, of the natural laws which give rise to or regulate them.
This simple method is that--and the only--method by which science advances. By this method, and by it only, do we acquire connected and systematic knowledge of all the phenomena of Nature of which the physical sciences are cognizant. It is only by the application of this Aristotelian method and philosophy that we can hope to acquire exact scientific knowledge of existing phenomena, or to become able to antic.i.p.ate the phenomena which are to distinguish the future. The Aristotelian method of observing facts, and of inductive reasoning with those facts as a basis, has taught the chemist the properties of the known elementary substances and their characteristic behavior under ascertained conditions, and has taught him the laws of combination and the effects of their union, enabling him to predict the changes and the phenomena, chemical and physical, which inevitably follow their contact under any specified set of conditions.
It is this process which has enabled the physicist to ascertain the methods of molecular motion which give us light, heat, or electricity, and the range of action and the laws which govern the transfer of energy from one of these modes of motion to another. It was this method of study which enabled James Watt to detect and to remedy the defects of the Newcomen engine, and it is by the Aristotelian philosophy that the engineer of to-day is taught to construct the modern steamship, and to predict, before the keel is laid or a blow struck in the workshop or the ship-yard, what will be the weight of the vessel, its cargo-carrying capacity, the necessary size and power of its engines, the quant.i.ty of coal which they will require per day while crossing the ocean, the depth at which the great hull will float in the water, and the exact speed that the vessel will attain when the engines are exerting their thousand or their ten thousand horse-power.
It was at Alexandria that this mighty philosophy was first given a field in which to work effectively. Here Ptolemy studied astronomy and "natural philosophy;" Archimedes applied himself to the studies which attract the mathematician and engineer; Euclid taught his royal pupil those elements of geometry which have remained standard twenty-two centuries; Eratosthenes and Hipparchus studied and taught astronomy, and inaugurated the existing system of quant.i.tative investigation, proving the spherical form of the earth; and Ctesibius and Hero studied pneumatics and experimented with the germs of the steam-engine and of less important machines.
When, seven centuries later, the destruction of this splendid inst.i.tution was signalized by the death of that brilliant scholar and heathen teacher of philosophy, Hypatia, at the hands of the more heathenish fanatics who tore her in pieces at the foot of the cross, and by the dispersion of the library left by Caesar"s soldiers in the Serapeum, a true philosophy had been created, and the inductive method was destined to live and to overcome every obstacle in the path of enlightenment and civilization. The fall of the Alexandrian Museum, sad as was the event, could not destroy the new philosophical method.
Its fruits ripened slowly but surely, and we are to-day gathering a plentiful harvest.
Science, literature, and the arts, all remained dormant for several centuries after the catastrophe which deprived them of the light in which they had flourished so many centuries. The armies of the caliphs made complete the shameful work of destruction begun by the armies of Caesar, and the Alexandrian Library, partly destroyed by the Romans, was completely dispersed by the Patriarchs and their ignorant and fanatical followers; and finally all the scattered remnants were burned by the Saracens. But when the thirst for conquest had become satiated or appeased, the followers of the caliphs turned their attention to intellectual pursuits, and the ninth century of the Christian era saw once more such a collection of philosophical writings, collected at Bagdad, as could only be gathered by the power and wealth of the later conquerors of the world. Philosophy once again resumed its empire, and another race commenced the study of the mathematics of India and of Greece, the astronomy of Chaldea, and of all the sciences which originated in Greece and in Egypt. By the conquest of Spain by the Saracens, the new civilization was imported into Western Europe and libraries were gathered together under the Moorish rulers, one of which numbered more than a half-million volumes. Wherever Saracen armies had extended Mohammedan rule, schools and colleges, libraries and collections of philosophical apparatus, were scattered in strange profusion; and students, teachers, philosophers, of all--the speculative as well as the Aristotelian--schools, gathered together at these intellectual ganglia, as enthusiastic in their work as were their Alexandrian predecessors. The endowment of colleges, that truest gauge of the intelligence of the wealthy cla.s.ses of any community, became as common--perhaps more so--as at the present time, and provision was made for the education of rich and poor alike. The mathematical sciences, and the wonderful and beautiful phenomena which--but a thousand years later--were afterward grouped into a science and called chemistry, were especially attractive to the Arabian scholars, and technical applications of discovered facts and laws a.s.sisted in a wonderfully rapid development of arts and manufactures.
When, a thousand years after Christ, the centre of intellectual activity and of material civilization had drifted westward into Andalusia, the foundation of every modern physical science except that now just taking shape--the all-grasping science of energetics--had been laid with experimentally derived facts; and in mathematics there had been erected a symmetrical and elegant superstructure. Even that underlying principle of all the sciences, the principle of the persistence of energy, had been, perhaps unwittingly, enunciated.
Distinguished historians have shown how the progress of civilization in Europe resulted in the creation, during the middle ages, of the now great middle cla.s.s, which, holding the control of political power, governs every civilized nation, and has come into power so gradually that it was only after centuries that its influence was seen and felt.
This, which Buckle[104] calls the intellectual cla.s.s, first became active, independently of the military and of the clergy, in the fourteenth century. In the two succeeding centuries this cla.s.s gained power and influence; and in the seventeenth century we find a magnificent advance in all branches of science, literature, and art, marking the complete emanc.i.p.ation of the intellect from the artificial conditions which had so long repressed its every effort at advancement.
[104] "History of Civilization in England," vol. i., p. 208. London, 1868.
Another great social revolution thus occurred, following another period of centuries of intellectual stagnation. The Saracen invaders were driven from Europe; the Crusaders invaded Palestine, in the vain effort to recover from the hands of the infidels the Holy Sepulchre and the Holy Land; and intestine broils and inter-state conflicts, as well as these greater social movements, withdrew the minds of men once more from the arts of peace and the pursuits of scholars. It is not, then, until the beginning of the seventeenth century--the time of Galileo and of Newton--that we find the nations of Europe sufficiently quiet and secure to permit general attention to intellectual vocations, although it was a half-century earlier (1543) that Copernicus left to the world that legacy which revolutionized the theories of the astronomers and established as correct the hypothesis which made the sun the centre of the solar system.
Galileo now began to overturn the speculations of the deductive philosophers, and to proclaim the still disputed principle that the book of Nature is a trustworthy commentary in the study of theological and revealed truths, so far as they affect or are affected by science; he suffered martyrdom when he proclaimed the fact that G.o.d"s laws, as they now stand, had been inst.i.tuted without deference to the preconceived notions of the most ignorant of men. Bruno had a few years earlier (1600) been burned at the stake for a similar offense.
Galileo was perhaps the first, too, to combine invariably in application the idea of Plato, the philosophy of Aristotle, and the methods of modern experimentation, to form the now universal scientific method of experimental philosophy. He showed plainly how the grouping of ascertained facts, in natural sequence, leads to the revelation of the law of that sequence, and indicated the existence of a principle which is now known as the law of continuity--the law that in all the operations of Nature there is to be seen an unbroken chain of effect leading from the present back into a known or an unknown past, toward a cause which may or may not be determinable by science or known to history.
Galileo, the Italian, was worthily matched by Newton, the prince of English philosophers. The science of theoretical mechanics was hardly beginning to a.s.sume the position which it was afterward given among the sciences; and the grand work of collating facts already ascertained, and of definitely stating principles which had previously been vaguely recognized, was splendidly done by Newton. The needs of physical astronomy urged this work upon him.
Da Vinci had, in the latter half of the fifteenth century, summarized as much of the statics of mechanical philosophy as had, up to his time, been given shape; he also rewrote and added very much to what was known on the subject of friction, and enunciated its laws. He had evidently a good idea of the principle of "virtual velocities," that simple case of equivalence of work, in a connected system, which has done such excellent service since; and with his mechanical philosophy this versatile engineer and artist curiously mingled much of physical science. Then Stevinus, the "brave engineer of Bruges," a hundred years later (1586), alternating office and field work, somewhat after the manner of the engineer of to-day, wrote a treatise on mechanics, which showed the value of practical experience and judgment in even scientific work. And thus the path had been cleared for Newton.
Meantime, also, Kepler had hit upon the true relations of the distances of the planets and their periodic times, after spending half a generation in blindly groping for them, thus furnishing those great landmarks of fact in the mechanics of astronomy; and Galileo had enunciated the laws of motion. Thus the foundation of the science of dynamics, as distinguished from statics, was laid, and the beginning was made of that later science of energetics, of which the philosophy of the steam-engine is so largely const.i.tuted.
Hooke, Huyghens, and others, had already seen some of the princ.i.p.al consequences of these laws; but it remained for Newton to enunciate them with the precision of a true mathematician, and to base upon them a system of dynamical laws, which, complemented by his announcement of the existence of the force of gravitation, and his statement of its laws, gave a firm basis for all that the astronomer has since done in those quant.i.tative determinations of size, weight, and distance, and of the movements of the heavenly bodies, which compel the wonder and admiration of mankind.
The Arabians and Greeks had noticed that the direction taken by a body falling under the action of gravitation was directly toward the centre of the earth, wherever its fall might occur; Galileo had shown, by his experiments at Pisa, that the velocity of fall, second after second, varied as the numbers 1, 3, 5, 7, 9, etc., and that the distances varied as the squares of the total periods of time during which the body was falling, and that it was, in British feet, very nearly sixteen times the square of that time in seconds. Kepler had proved that the movements of the heavenly bodies were just such as would occur under the action of central attractive forces and of centrifugal force.
Putting all these things together, Newton was led to believe that there existed a "force of gravity," due to the attraction, by the great ma.s.s of the earth, of its own particles and of neighboring bodies, like the moon, of which force the influence extended as far, at least, as the latter. He calculated the motion of the earth"s satellite, on the a.s.sumption that his theory and the then accepted measurements of the earth"s dimensions were correct, and obtained a roughly approximate result. Later, in 1679, he revised his calculations, using Picard"s more accurate determination of the dimensions of the earth, and obtained a result which precisely tallied with careful measurements, made by the astronomers, of the moon"s motion.
The science of mechanics had now, with the publication of Newton"s "Principia," become thoroughly consistent and logically complete, so far as was possible without a knowledge of the principles of energetics; and Newton"s enunciations of the laws of motion, concise and absolutely perfect as they still seem, were the basis of the whole science of dynamics, as applied to bodies moving freely under the action of applied forces, either constant or variable. They are as perfect a basis for that science as are the primary principles of geometry for the whole beautiful structure which is built up on them.
The three perfect qualitative expressions of dynamical law are:
1. Every free body continues in the state in which it may be, whether of rest or of rectilinear uniform motion, until compelled to deviate from that state by impressed forces.
2. Change of motion is proportional to the force impressed, and in the direction of the right line in which that force acts.
3. Action is always opposed by reaction; action and reaction are equal, and in directly contrary directions.
We may add to these principles a definition of a force, which is equally and absolutely complete:
_Force_ is that which produces, or tends to produce, motion, or change of motion, in bodies. It is measured statically by the weight that will counterpoise it, or by the pressure which it will produce, and dynamically by the velocity which it will produce, acting in the unit of time on the unit of ma.s.s.
The quant.i.tative determinations of dynamic effects of forces are always readily made when it is remembered that the effect of a force equal to its own weight, when the body is free to move, is to produce in one second a velocity of 32.2 feet per second, which quant.i.ty is the unit of dynamic measurement.
_Work_ is the product of the resistance met in any instance of the exertion of a force, into the distance through which that force overcomes the resistance.
_Energy_ is the work which a body is capable of doing, by its weight or inertia, under given conditions. The energy of a falling body, or of a flying shot, is about 1/64 its weight multiplied by the square of its velocity, or, which is the same thing, the product of its weight into the height of fall or height due its velocity. These principles and definitions, with the long-settled definitions of the primary ideas of s.p.a.ce and time, were all that were needed to lead the way to that grandest of all physical generalizations, the doctrine of the persistence or conservation of all energy, and to its corollary declaring the equivalence of all forms of energy, and also to the experimental demonstration of the transformability of energy from one mode of existence to another, and its universal existence in the various modes of motion of bodies and of their molecules.
Experimental physical science had hardly become acknowledged as the only and the proper method of acquiring knowledge of natural phenomena at the time of Newton; but it soon became a generally accepted principle. In physics, Gilbert had made valuable investigations before Newton, and Galileo"s experiments at Pisa had been examples of similarly useful research. In chemistry, it was only when, a century later, Lavoisier showed by his splendid example what could be done by the skillful and intelligent use of quant.i.tative measurements, and made the balance the chemist"s most important tool, that a science was formed comprehending all the facts and laws of chemical change and molecular combination. We have already seen how astronomy and mathematics together led philosophers to the creation and the study of what finally became the science of mechanics, when experiment and observation were finally brought to their aid. We can now see how, in all these physical sciences, four primitive ideas are comprehended: matter, force, motion, and s.p.a.ce--which latter two terms include all relations of position.
Based on these notions, the science of mechanics comprehends four sections, which are of general application in the study of all physical phenomena. These are:
_Statics_, which treats of the action and effect of forces.
_Kinematics_, which treats of relations of motion simply.
_Dynamics_, or kinetics, which treats of simple motion as an effect of the action of forces.
_Energetics_, which treats of modifications of energy under the action of forces, and of its transformation from one mode of manifestation to another, and from one body to another.
Under the latter of these four divisions of mechanical philosophy is comprehended that latest of the minor sciences, of which the heat-engines, and especially the steam-engine, ill.u.s.trate the most important applications--_Thermo-dynamics_. This science is simply a wider generalization of principles which, as we have seen, have been established one at a time, and by philosophers widely separated both geographically and historically, by both s.p.a.ce and time, and which have been slowly aggregated to form one after another of the sciences, and out of which, as we now are beginning to see, we are slowly evolving wider generalizations, and thus tending toward a condition of scientific knowledge which renders more and more probable the truth of Cicero"s declaration: "One eternal and immutable law embraces all things and all times." At the basis of the whole science of energetics lies a principle which was enunciated before Science had a birthplace or a name:
_All that exists, whether matter or force, and in whatever form, is indestructible, except by the Infinite Power which has created it._
That matter is indestructible by finite power became admitted as soon as the chemists, led by their great teacher Lavoisier, began to apply the balance, and were thus able to show that in all chemical change there occurs only a modification of form or of combination of elements, and no loss of matter ever takes place. The "persistence" of energy was a later discovery, consequent largely upon the experimental determination of the convertibility of heat-energy into other forms and into mechanical work, for which we are indebted to Rumford and Davy, and to the determination of the quantivalence antic.i.p.ated by Newton, shown and calculated approximately by Colding and Mayer, and measured with great probable accuracy by Joule.
[Ill.u.s.tration: Benjamin Thompson, Count Rumford.]
The great fact of the conservation of energy was loosely stated by Newton, who a.s.serted that the work of friction and the _vis viva_ of the system or body arrested by friction were equivalent. In 1798, Benjamin Thompson, Count Rumford, an American who was then in the Bavarian service, presented a paper[105] to the Royal Society of Great Britain, in which he stated the results of an experiment which he had recently made, proving the immateriality of heat and the transformation of mechanical into heat energy. This paper is of very great historical interest, as the now accepted doctrine of the persistence of energy is a generalization which arose out of a series of investigations, the most important of which are those which resulted in the determination of the existence of a definite quantivalent relation between these two forms of energy and a measurement of its value, now known as the "mechanical equivalent of heat." His experiment consisted in the determination of the quant.i.ty of heat produced by the boring of a cannon at the a.r.s.enal at Munich.