Ericsson's (1883) employed a portion of a parabolic cylinder as a reflector to collect and concentrate the rays of the sun; this reflector was in fact a trough, its bottom or well being composed of wooden staves which were supported by ribs of parabolic curvature, and on which there were reflecting plates of glass silvered on the under side. The apparatus is shown in perspective in Figure i (ffi. o7); a part of it is shown in transverse section in Figure 2, where the direct and the reflected solar rays are shown by vertical and by diagonal lines. It is described by its distinguished inventor, the late Captain John Ericsson, as follows: " It will be seen that the trough, II feet long and 16 feet broad, includ ing a parallel opening in the bottom 12 inches wide, is sustained by a light truss attached to each end, the heater being supported by vertical plates secured to the truss. The heater is inches in diameter, II feet long, exposing 13o X 9.8 = 1274 superficial inches to the action of the reflected solar rays. The reflecting plates, each 3 inches wide and 26 inches long, intercept a sunbeam of 130 X iSo = 23,40o square inches' section. The trough is supported by a central pivot round which it revolves. The change of inclination is effected by means of a horizon tal axle (not seen in the Figure), the entire mass being so accurately bal anced that a pull of five pounds applied at the extremity enables a person to change the inclination or to cause the whole to revolve. A single revolu tion of the motive engine develops more power than is needed to turn the trough and to regulate its inclination so as to face the sun during a day's operation.
The motor is a steam-engine (fig. i), the working cylinder being 6 inches in diameter with 8 inches' stroke. The piston-rod, passing through the bottom bf the cylinder, operates a force-pump of 5 inches' diameter. By means of an ordinary cross-head secured to the piston-rod below the steam-cylinder and by ordinary connecting-rods, motion is imparted to a crank-shaft and fly-wheel applied at the top of the engine frame; it being the object of this arrangement to show the capability of the engine to work either pumps or mills. It should be noticed that the flexible steam pipe employed to convey the steam to the engine, as well as the steam chamber attached to the upper end of the beater, has been excluded in the illustration. The average speed of the engine during the trials (1883) was one hundred and twenty turns per minute, the absolute pressure on the working piston being thirty-five pounds per square inch. The steam was worked expansively in the ratio of i to 3, with a nearly perfect vac uum kept up in the condenser inclosed in the pedestal which supports the engine-frame." speaking, there is no such thing as a vapor engine as distinguished from a gas-engine. Almost any inflammable or explosive vapor can be used in an ordinary gas-engine with but very little change, the difference between a vapor and a gas being largely dependent upon temperature.
seeking other motive fluids than water cheap ness was kept in view so long as it had to be applied to a machine from which it must escape after being used. Water, air, combustion gases, and even illuminating gas, answered the requirements better than most other substances. But, as there are steam-engines in which the steam is con densed and used repeatedly, and caloric engines in which cooling arrange ments permit the repeated use of the same fluid, the question of cheapness of motive fluid becomes less important. For such closed motors ether, bisulphide of carbon, and ammonia have been used. Ether evaporates at 33° Cent. and acquires a tension of nearly nine atmospheres at ioo°, while saturated steam at this temperature has only one atmosphere. Hence, by using the exhaust from a steam-engine, ether may be evaporated at a consid erable tension and its vapor be used in an engine constructed like the steam engine and placed alongside thereof, so that this auxiliary motor is practi cally worked without any fuel. Tremblay, Delaporte, Tellier, and others have produced engines upon this principle. The chief objection to ether as a motive fluid is due to the impossibility of preventing leaks, and, the material being both expensive and highly inflammable, the objection is a serious one. The same may be urged against alcohol, naphtha, etc. Bisul phide of carbon seems to be the most promising fluid for use in this con nection.
any gas-engine can be used with oil as a motive fluid by adding a pumping attachment by which the oil can be " atom ized " or sprayed so as to enter the igniting chamber in such a highly divided state as to be explosive when mixed with the proper proportion of air.
plain steam-engine can be run with compressed air if care be taken to have the air dry, so that the exhaust orifice will not become clogged by the snow formed when moist air is released from compression. It must be remembered, however, that air will not work expansively like steam. Most rock-drills can be driven either by compressed air or by steam. As a means of transmitting power to a distance, compressed air has the advantage over steam, as the air loses nothing in force by reason of radiation from the containing pipes, and in mines it not only aids in ventilating, but has the advantage of not rotting the timbers as does the exhaust steam.
air has been tried as an auxiliary to steam for the purpose of re-evaporating the water formed by radiation and internal condensation; the principle on which it acts being that recently compressed air at a given pressure has a higher temperature than ordinary steam at the same tension. The heat of compression, instead of going to heat the containing vessel, is largely absorbed by the water held by the steam. In this respect the air has the effect of a superheating jacket; but its use calls for increased size of cylinders and pipes. (R. G.)