2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



mechanical forms. As efficient production of solar power must never- 

 theless be the first step, I shall postpone considerations of storage for 

 the present. 



WATER DISTILLING AND COOKING BY SOLAR HEATING 



There are other uses for solar heating which do not so much involve 

 storage. Among them are the distillation of water and the cooking 

 of food. It is stated that in Bermuda the past year was so deficient 

 in rainfall that fresh water was imported from New York, although 

 the Atlantic ocean is all around. In some of our western States the 

 water in many parts is too alkaline for drinking or for storage 

 batteries. In Florida the water in some localities stinks with hydrogen 

 sulphide. Under such conditions as these the solar distilling device 

 should be useful. As for cooking, though not practical in cloudy 

 regions, it is easy to provide heat storage for 24 hours, and with a 

 solar cooking device the ovens may be kept at baking temperatures 

 for weeks and months continuously in the more cloudless parts of 

 our country. 



RECENT COMMERCIAL PRODUCTS A BOON TO SOLAR DEVICES 



The cheap production of efficient solar heat devices has awaited 

 the commercial development of aluminum products, now so plenti- 

 fully used in the industries, and the common use of vacuum devices, 

 which came with the incandescent lamp and radio industries. For- 

 merly, inventors relied on glass mirrors which were heavy, costly, 

 and not durable. It is now possible to purchase the so-called "Alcoa" 

 in thin sheets, which readily take the curvature of a suitable cradle 

 form without previous shaping. This material reflects over 80 percent 

 of solar radiation, and may be used for years without dimming. As 

 the loss of heat in the boiler at the focus of a solar-radiation appliance 

 is the great obstacle to be provided against, the possibility of making 

 cheap glass jackets enclosing high vacua like thermos bottles is the 

 other great improvement which has become practicable in recent times. 



MECHANISM FOR FOLLOWING THE SUN 



The daily march of the sun through the sky, and its yearly march 

 from north to south, must be considered. If one uses a spherical 

 boiler and a circular mirror, he must allow for both of these apparent 

 motions as Eneas did at the ostrich farm, Pasadena, about 1905. If, 

 however, one uses a tubular boiler parallel to the axis of the earth, 



