Page:Popular Science Monthly Volume 9.djvu/581

Rh, forming an annular envelope three centimetres in thickness. Thus the volume of liquid is twenty litres, and the steam-chamber has a capacity of ten litres. The inner envelope is empty. Into it pass the steam-pipe and the feed-pipe of the boiler. To the steam-pipe are attached the gauge and the safety-valve. The bell-glass covering the boiler is eighty-five centimetres high, forty centimetres in diameter, and five millimetres in thickness. There is everywhere a space of five centimetres between its walls and those of the boiler, and this space is filled with a layer of very hot air.

The earth, owing to its diurnal and annual revolution, does not occupy the same position with regard to the sun at all hours of the day, or in all seasons of the year. This being the case, the generator is so contrived as to revolve 15°, or one twenty-fourth of its circumference, hourly around an axis parallel to the earth's axis, i. e., so as to follow the apparent diurnal motion of the sun, and to incline gradually on this axis in proportion to the solar declination. Hence the intensity of the utilized heat is always nearly the same, whatever the hour of the day or the season of the year, inasmuch as the apparatus is always so arranged as to reflect with the least possible loss all the rays emitted by the sun. This double motion of the generator is effected by a very simple contrivance.

The generator just described is the one which M. Mouchot was enabled three years and a half ago to set up at Tours, the Conseil Général of Indre-et-Loire having provided the funds. It has yielded curious results, some of which are worthy of being recorded here, though before long they will be surpassed, when some improvements have been made in the apparatus. On May 8, 1875, the weather being fine, twenty litres of water at 20° C. temperature was introduced into the boiler at 8.30, and took only forty minutes to produce steam with a pressure of two atmospheres; in other words, a temperature of 121° C. was obtained, which is 21° centigrade degrees above boiling-point. This steam then quickly acquired a pressure of five atmospheres. This was the safety limit of the strength of the apparatus: if the process had been carried any further the boiler would have exploded. Toward noon on the same day, with fifteen litres of water in the boiler, steam at 100° C., i. e., a pressure of one atmosphere, was raised in less than fifteen minutes to five atmospheres—a temperature of 153° C. Finally, on July 22d, about one hour after mid-day, the heat being exceptionally great, the apparatus reduced to vapor five litres of water per hour, which is equal to one hundred and forty litres of steam per minute, or half a horse-power.