INDUSTRIAL APPLICATIONS OF SOLAR HEAT. 55 1 



from the sun and poured down upon the earth in one year would suf- 

 fice to melt a sheet of ice thirty metres thick, and enveloping the 

 entire globe. 



About the year 1860, M. Mouchot, then Professor of Mathematics 

 iu the Lycee of Alencon, being stimulated by the researches of Pouillet 

 as well as by those of Melloni, the ablest of Italian physicists, who 

 has made experiments of incomparable precision upon the transmis- 

 sion of heat, boldly attacked the question of the utilization of the 

 sun's heat. The mechanical equivalent of heat had at length been 

 determined. Thanks to Melloni, we already knew the quantity of 

 caloric which different bodies, as glass, when reduced to thin lamina?, 

 suffer to pass through, as also the difference in the reflecting power 

 of polished metallic surfaces according to the nature of the metals, 

 employed. But to measure the amount of vis viva transmitted daily 

 from the sun to the earth, and, more Utopian still, to concentrate, at 

 little cost, the sun's rays, so as to realize all the effects of which they 

 are capable, were objects the attainment of which was henceforth in- 

 sured, though Buffon and Saussure had failed, owing to the insuffi- 

 ciency of the data at their command. The question is now merely a 

 matter of calculation, an application of well-known physical laws. 



In order to concentrate to any useful purpose the sun's rays, there 

 was need of a receiver which should be of moderate size and reasona- 

 ble cost. After sundry attempts, one of which was with an apparatus 

 resembling that of Saussure, Mouchot contrived a vertical boiler of 

 copper, blackened on the outside, covered with three concentric bell- 

 glasses, and resting on some bad conductor of heat, as sand, brick, or 

 wood. Soon he increased the power of his apparatus by the addition 

 of a metallic reflector, which enabled him to dispense with two of the 

 three bell-glasses. With this apparatus he considerably raised the 

 temperature of the water in the boiler, reduced it to vapor, melted 

 sulphur, the liquefaction temperature of which is 116 C, and after 

 twenty minutes of insolation brought the empty boiler up to the tem- 

 perature of 200 C. 



With this reflector a few seconds suffice to set on fire a heap of 

 shavings or a piece of board. In a glass vessel placed at the focus 

 of the reflector and inclosed in another vessel of glass, one kilogramme 

 of tin has been melted in two minutes ; the same quantity of lead took 

 five minutes, and of zinc, six. The fusion-point of these three metals 

 is 235, 335, and 475 C. respectively. With spherical or parabolic 

 mirrors, whose focus is a point, and not a line, as in the conical or 

 cylindrical min-ors employed in the foregoing experiments, the con- 

 centration of solar heat would have been still stronger. 



While engaged in these investigations, the ingenious experimenter 

 brought out bis Marmite Solaire, a cylindrical glass vessel, in which 

 is placed another cylinder of copper or of wrought-iron blackened on 

 the outside, and resting on the bottom of the glass receiver. The 



