552 THE POPULAR SCIENCE MONTHLY. 



whole is covered with a glass lid. A cylindrical reflector of silver 

 directs the sun's rays upon the apparatus. With this marmite it 

 takes less than four hours to prepare an excellent pot-au-feu, consist- 

 ing of one kilogramme of beef and a quantity of vegetables, the whole 

 being perfectly cooked, and very palatable, owing to the fact of the 

 heat being applied with great regularity. 



In this form of marmite, now superseded by a simple glass vessel 

 fixed at the focus of a conical mirror of silver-plated brass, fruits, 

 potatoes, all sorts of legumes, meats, and grains, are cooked by solar 

 heat. So, too, an infusion of tea or coffee can be readily prepared, and 

 for this purpose we may employ one of those bottles of colored glass 

 in which Lyons beer is put up. To cook legumes or grains rapidly, a 

 different course may be taken. A closed vessel containing water is 

 set in the focus of the reflector, and, when the liquid begins to boil, 

 the upper portion of the vessel is connected by a tube with the bot- 

 tom of another containing the legumes or grains, which are quickly 

 cooked by the steam. 



To transform the marmite into an oven, a disk of wrought-iron is 

 placed beneath the glass lid, and in less than three hours a kilogramme 

 of bread is baked. The crust is hard and brown, and the pith light 

 and well raised, as with bread baked in an ordinary oven. 



The roasting of meat, not requiring the same amount of heat as 

 does the vaporization of an equal weight of water, can be performed 

 in the open air, by the action of the solar reflector alone, the piece of 

 beef, veal, or mutton being fixed upon a spit. In less thau an hour we 

 have in this way a very fine roast. The use of butter must be avoided, 

 lest the chemical rays, by transforming the butter into butyric acid, 

 should spoil the flavor of the meat. By interposing a pane of green 

 or red glass we can intercept the chemical rays which cause this fer- 

 mentation, and then the result leaves nothing to be desired. 



By substituting for the two lids of the solar marmite an alembic- 

 head, the apparatus can be used for the purposes of distillation. To 

 this end the alembic-head is connected, by an horizontal tube, with a 

 worm, the latter descending in the form of a helix and dipping into a 

 constant current of cold water, while the metallic vessel, containing 

 two litres of wine, is inclosed in the glass cylinder and set in the 

 focus of the reflector. The alcohol is collected after forty minutes 

 of exposure to the sun. Inasmuch as the apparatus grows hot slowly 

 and continuously, the alcohol is highly concentrated and possesses a 

 very agreeable aroma. 



In all the foregoing experiments, M. Mouchot at first used concave 

 silver mirrors, cylindro-parabolic in form, i. e., cylindrical mirrors whose 

 base-line is an open curve resembling a parabola. The reflecting 

 power of cylindrical mirrors increases in proportion to their aperture, 

 and hence the time required, for instance, to boil a litre of water is 

 inversely as the aperture of the mirror, i. e., the greater the aperture 



