100 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



fection. The mirror, which is of parabolic cylindrical shape, about 10 

 feet long and 7 feet wide, brings the solar radiation to focus on a tube 

 filled with oil which passes up the axis of the mirror, parallel to the 

 earth's axis, and about this tube, on suitable rollers, the mirror is 

 rotated by means of a simple and inexpensive clockwork, in order that 

 it may always face toward the sun. The oil tube is connected with a 

 reservoir of oil about 10 feet higher up and from this a return tube 

 goes underneath the mirror, thus completing the circuit for the 

 flow of oil which the mirror, by focusing the sun rays, strongly 

 heats. The reservoir contains about a barrel of oil, which is such 

 as is used for lubricating gas-engine cylinders. The reservoir and 

 the oil circuit tubes are protected from the loss of heat, as far as 

 possible, by insulation. The greatest loss of heat, however, occurs 

 with the naked tube which passes through the mirror. This, how- 

 ever, is protected by a glass tube 4 inches in diameter, and this, in 

 turn, by flat sheets of glass covering the whole mirror and protecting 

 it from dust and wind. Two ovens are inserted in the rear of the 

 reservoir, which is just outside the door of the observer's cottage 

 on Mount Wilson, and food after being prepared in the kitchen, 

 may be baked, boiled, or stewed in these ovens, according to the 

 character of the dish. Nearly all of the food prepared for the use 

 of the observers during their stay on Mount Wilson, from July 1 to 

 September 15, was cooked by this solar cooker. The great advantage 

 of the cooking is that the reservoir stays hot for a good many hours, 

 so that cooking may be continued through the night or even through 

 a partially cloudy day. The apparatus proved to be especially satis- 

 factory for the canning of fruit. 



In the early part of September Messrs. Abbot and Aldrich packed 

 the apparatus which had been used on Mount Wilson for observing 

 the solar constant of radiation and shipped the same to Wenden, 

 Ariz., the nearest railroad station leading to Mount Harqua Hala. 

 The apparatus was set up for observations by the end of September, 

 and Doctor Abbot, with Mr. F. A. Greeley as assistant, carried on 

 solar radiation measurements beginning October 3 continuously 

 until January 20, 1921, when Doctor Abbot was relieved by Mr. L. B. 

 Aldrich, who in turn was relieved by Mr. A. F. Moore, formerly 

 director of the observatory at Calama and Montezuma, Chile, who 

 reported for duty about April 20. It is intended to carry on the 

 solar constant observations at Mount Harqua Hala on all days when 

 the weather permits for several years in cooperation with the similar 

 observations being made at Montezuma, Chile. With the results of 

 the two stations, it is hoped to furnish a sound basis for the study of 

 . solar variation and the dependence of terrestrial weather conditions 

 thereon. The station at Mount Harqua Hala was erected after a 



