A steam-engine consists of two principal parts, the boiler and the engine proper, or motor. We suppose that with the boiler employed at Tours we can use the common motors; this is one of the advantages possessed by the solar apparatus, viz., that it does not require a special form of motor. At first the inventor employed for his demonstrations a double-acting engine, without either condensation or detention of steam, the cylinder of which had a capacity of one-third of a litre. This engine performed eighty strokes per minute, with a steady pressure of one atmosphere; it continued to work even under a slightly-clouded sun. This was later superseded by a rotary engine, that is, an engine with revolving cylinder, which avoids all transmission of movement; but the system is faulty. Yet this engine worked very well, driving at high velocity a little pump for raising water; the pump, however, being of weak construction, became disabled. It is a pity that the inventor has never measured the real work performed by his engine, by means of a dynamometer.
The solar reflector, being first of all a furnace using fuel that costs nothing, is not only of use as a means of developing motive force, but can also be employed for a multitude of purposes—for instance, distilling water to make it fit for drinking, concentrating and crystallizing saline solutions, preparing alcohol, etc. Five litres of wine can be distilled in a quarter of an hour by passing the vapor from the apparatus into a still. The manufacture of alcohol from grain, sugarcane, or beet-root, would be equally easy. The steam generated by this apparatus can also be employed for cooking fodder for cattle. M. Mouchot has devised a form of small marmites, quite different from his large steam-generator. These can be used by hunters for preparing their meals, and explorers of great deserts will now have something besides camel or buffalo chips for cooking their victuals.
Many and varied are the uses of this curious invention. The aëronaut can with its aid propel his air-ship. Hot-air motors and ammonia engines will be benefited by the use of the solar receiver; but it is especially in tropical countries that it is destined to find immediate employment, in driving the various kinds of machinery used in sugar and cotton plantations, in distilling impure water to make it fit for drinking, in crystallizing saline and saccharine solutions, in pumping water of irrigation, in manufacturing ice by means of the Carré machine, etc. In those countries fuel is scarce, firewood is not abundant, and coal, which has to be imported from a distance, often from the mines of England, commands an exorbitant price. Already in southern countries sea-salt is obtained purely by the action of solar heat. In Chili and in Mauritius, salt-marshes are divided into compartments, with walls and roof of glass, in order to promote evaporation; so in the famous nitre-beds of Iquique, on the coast of Peru, the salt might be crystallized by solar heat alone.
The cost of a solar apparatus of half a horse-power, like that
