IXDUSTRIAL APPLICATIONS OF SOLAR HEAT. 555 



lopes, 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 circum- 

 ference, 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 appa- 

 ratus 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 

 General 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 be- 

 ing fine, twenty litres of water at 20 C. temperature was introduced 

 into the boiler at 8.80 A. M., and took only forty minutes to produce 

 steam with a pressure of two atmospheres ; in other words, a tempera- 

 ture of ]21 C. was obtained, which is 21 centigrade degrees above 

 boiling-point. This steam then quickly acquired a pressure of five atmos- 

 pheres. This was the safety limit of the strength of the apparatus : if 

 the process had been carried any further the boiler would have explod- 

 ed. Toward noon on the same day, wdth 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. 1 



1 A maker of instruments of precision, J. Salleron, who constructed the solar appa- 

 ratus which was presented to the Institut last year, lately wrote to me as follows : " I 

 have driven a small model steam-engine, with the steam generated in the boiler of this 

 new generator, and M. Noel, Professor of Physics in the Vendome Lycee, put the same 

 engine in operation on January 5th last. The water began to boil after twenty-eight 

 minutes, the hour being noon, and the temperature of the surrounding air near C." 



