Robert Henry Thurston

“ STEAM-NAVIGATION.
72. Among the most interesting of the applications of steam-power, to the political economist and to the historian, as well as to the engineer, is its use in ship-propulsion.
In the modern marine engine we find one of the most important adaptations of steam machinery and the greatest of all the triumphs of the mechanical engineer. ”

“ In 1815, therefore, we may say that the modern locomotive steam-engine came into existence, for it is this invention of the blast-pipe that gives it its life, and it is the mechanical adaptation of this and of the other organs of the steam-engine to locomotion that gives George Stephenson his greatest claim to distinction. ”

“ He whose inventive genius, or mechanical skill, contributes to effect either of these objects—to secure either the use of higher steam with safety, or the more effective conversion of heat into mechanical power without waste, or the reduction, by transformation into work, of the temperature of the rejected working-fluid—confers an inestimable boon upon mankind. ”

“ The time has gone by when, in any art, the ignorant and merely dexterous workman can compete with even a less skillful shopmate, who possesses and uses brains as well as hands, and knows how to make the one direct and aid the other. We to-day find him occupying a decided vantage-ground who is at the same time familiar with the schools and at home in the workshop. For whatever department in the arts a youth may be designed, he must, to insure success in the future, be taught not "in either the school or the workshop," the alternative formerly offered him, but in the school and the workshop. ”

“ But it is sufficiently evident that, before the engineer can determine what form of machine will best yield to him full control of these forces of Nature, he must have sufficient knowledge of science to be able to understand what scientific principles are to be rendered available, and what phenomena of Nature are operating in the production of the power which he is to seize upon and usefully to apply. ”

“ In management, there is an immense field for improvement, which improvement we may feel assured will rapidly take place, as it is now becoming well understood that care, skill, and intelligence, are absolutely essential to economical management, as well as to safety, and that they repay liberally all the expenditure of time and money that is requisite to secure them. It is truer of labor than of anything else in the market that "the best is the cheapest." ”

“ The history of the steam-engine is a subject that interests greatly every intelligent mind.
As Religion has always been, and still is, the great moral agent in
civilizing the world, and as Science is the great intellectual promoter of civilization, so the steam-engine is, in modern times, the most important physical agent in that great work. ”

“ Frequently, an important invention is made before the world is ready to receive it, and the unhappy inventor is taught, by his failure, that it is as unfortunate to be in advance of the age as to be behind it.
Inventions only become successful when they are not only needed, but when mankind is so far advanced in intelligence as to appreciate and to express the necessity for them, and at once to make use of them. ”

“ So, also, in developing the rise of a machine, a coarse instrument or a toy may be recognized as the germ of that production of mechanical genius whose power and usefulness have stimulated our curiosity to mark its changes and to trace its origin. ”

“ Now our large screw-steamers are of higher speed than any paddle-steamers on the ocean, sometimes crossing the Atlantic from New York to Queenstown in a week, making their passages with wonderful regularity, and developing their power at far less cost than the old side-wheel steamers. This increased economy is due, not only to the use of a more efficient propelling instrument, but, perhaps in even a higher degree, to the economy which has followed as a consequence of the accompanying changes in structure of the steam-engine driving it. ”

“ A machine, receiving at distant times and from many hands new combinations and improvements, and becoming at last of signal benefit to mankind, may be compared to a rivulet, swelled in its course by tributary streams until it rolls along a majestic river, enriching in its progress provinces and kingdoms. ”

“ There is certainly no creation of art that can be grander in appearance than a transatlantic steamer, a hundred and fifty yards in length, and weighing, with her stores, 5,000 or 6,000 tons, as she starts on her voyage, moved by engines more than equal in power to the united strength of 5,000 horses. Nothing can more thoroughly awaken a feeling of awe than the sight of immense structures like the great modern iron-clads (Fig. 65) , vessels having a total weight of 8,000 to 10,000 tons ”

“ Subsequently, Evans continued to extend the application of his engine and to perfect its details, and, others following in his track, the non-condensing engine is to-day fulfilling the predictions which he made seventy years ago, when he said:
"I have no doubt that my engine will propel boats against the currents of the Mississippi, and wagons on turnpike-roads, with great profit. . . . "The time will come when people will travel in stages moved by steam engines, from one city to another, almost as fast as birds can fly—fifteen or twenty miles an hour. ”

“ With steam-power, the gain by careful grading and excellence of construction of the road-bed becomes still more important. The animal mechanism is less affected in its power of drawing heavy loads than is the machine. With the horse, a bad road impedes transportation principally by resisting the movement of the load rather than of the animal, while with the traction-engine the motor is as seriously retarded as the train which follows it, and frequently much more, on soft ground. ”

“ The necessary weight and inertia are afforded in many cases, where the engine is applied to the pumping of deep mines, by the immensely long and heavy pump-rods. Where this weight is too great, it is counterbalanced; and where, as when used for the water-supply of cities, too small, weights are added. When the stroke is completed, the "equilibrium-valve" is opened, and the steam passes from above to the space below the piston, and, an equilibrium of pressure being thus produced, the pump-rods descend, forcing the water from the pumps and raising the steam-piston. ”

“ The teachings of science indicate that, in the modern steam-engine: Success in economically deriving mechanical power from the energy of heat-motion will 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. ”

“ The success of the Newcomen engine naturally attracted the attention of mechanics, and of scientific men as well, to the possibility of making other applications of steam-power.
The greatest men of the time gave much attention to the subject; but, until James Watt began the work that has made him famous, nothing more was done than to improve the proportions and to slightly alter the details of the Newcomen and Cawley engine, even by such skillful engineers as Brindley and Smeaton. ”

“ Whether this type of heat-engine can ever be made of practical value will be determined by the rate of condensation of steam expanding against a resisting piston; the extent to which high pressures and great expansion can be practically carried; the extent to which internal transfer of heat, without doing work, can be reduced; the practical limit of engine-speed; and the perfection attainable in the engine considered as a piece of mechanism. ”

“ It has at last become generally known, as was seen by well-informed and scientific engineers long ago, that one of the most serious losses of heat, and consequently of power, in the steam-engine, when expansion is carried to a considerable extent, occurs in consequence of condensation and the deposition of moisture upon the interior of the cylinder, which moisture, when the exhaust takes place, carries, by its reëvaporation, large quantities of heat into the condenser, without deriving any power from it. ”

“ The valve-gear of this engine is peculiarly well adapted to this type of engine. There is no fly-wheel, and the motion of each of the two independent engines, which together form the pair, is controlled by its neighbor, the valve-gear of the one being moved by the piston of the other. This ingenious combination permits each piston to move from end to end of its cylinder, holds it stationary an instant while the pump-cylinders come completely filled and their valves closed, and then sets it in motion on the return-stroke. ”

“ The earliest clays of screw propulsion witnessed the use of steam of ten or fifteen pounds' pressure, in a geared engine using jet condensation, and giving a horse-power at an expense of, perhaps, seven or eight pounds of coal per hour.
A little later came direct-acting engines with jet condensation, and steam at twenty pounds' pressure, costing about five or six pounds per horse-power per hour. The steam-pressure rose a little higher with the use of greater expansion, and the economy of fuel was further increased. ”

“ The second, How shall we construct a machine that shall most efficiently embody and accord with not only known scientific principles, but also with all well-settled principles of engineering practice? ”

“ It has increased the sum of human happiness, not only by calling new pleasures into existence, but by so cheapening former enjoyments as to render them attainable by those who before could never have hoped to share them. ”

“ Scientific research has proved that, in all varieties of heat-engines, a very great loss of effect is unavoidable from the fact that we cannot reduce the lower limit of temperature, in working, below a point that is far above the absolute zero of temperature: the point corresponding to the mean temperature of the surface of the earth in our latitude is now practically our lower mean limit of temperature. ”

“ Locomotives are now built weighing seventy tons, and powerful enough to draw more than 2,000 tons at a speed of twenty miles an hour. The modern locomotive consists of a boiler, mounted upon a strong light frame of forged iron, by which it is connected with the wheels. The largest engine yet constructed in the United States is said to be one in use on the Philadelphia & Reading Railroad, having a weight of about 100,000 pounds, which is carried on twelve driving-wheels. ”

“ Without general and systematic technical and trade education, the most enterprising people on the globe, brought into competition in the markets of the world with better-educated people and with nations of trained artisans, must inevitably become a great nation of paupers. ”

“ In attempting improvement in the directions that I have indicated, it would be the height of folly to assume that we have reached a limit in any one of them, or that we have even approached an impassable limit. If further progress seems checked by inadequate returns, when efforts are made to advance, in any promising direction, beyond present practice, it becomes the duty of the engineer to detect the cause of such hinderance, and, having found it, to find a way to remove it, if such removal is not physically impossible. ”

“ To return the rejected steam with its charge of heat—which usually forms so large a proportion of the total heat generated by the combustion of the fuel, assuming all transfer of heat to the exhaust by the operation of internal condensation and reëvaporation to have been prevented—demands the expenditure of precisely the amount of power which has been developed by its expansion. In an ideal engine of this type, therefore, the efficiency is perfect, and all heat-energy is utilized by transformation into mechanical energy ”

“ In detail, in the engine proper the tendency is, and may be expected to continue, in the near future at least, toward higher steam, greater expansion in more than one cylinder, steam-jacketing, superheating, a careful use of non-conducting protectors against waste, and higher piston-speed with rapid rotation, and to the adoption of special proportions and of forms of valve-gear adapted to such high-speed engines. ”

“ The higher the temperature of the steam, however, when it enters the engine, and the lower the temperature at which it leaves the cylinder, and the more thoroughly we provide against waste of heat by conduction and radiation, and of power by friction, the greater will be our success. ”

“ The absence of the crank or other device which might determine absolutely the length of stroke compels a very careful adjustment of steam admission to the amount of load. Should the stroke be allowed to exceed the proper length, and should danger thus arise of the piston striking the cylinder-heads, the movement is checked by buffer-beams. The regulation is effected by a "cataract," a kind of hydraulic governor, consisting of a plunger-pump with a reservoir attached. The plunger is raised by the engine, and then automatically detached. ”

“ It is at once evident that the only way in which any very great additional economy can be secured is to reduce to a minimum the quantity of heat remaining at the opening of the exhaust-valve, and then to retain this rejected heat within the system, so far as is possible, and to thus prevent its waste by escape from the system. ”