108 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1&24 



ment maker, Mr. Kramer, who was engaged in making the Aus- 

 tralian and Argentine solar radiation outfits, no work had been done 

 toward mounting the optical parts for ozone studies or, indeed, to- 

 ward preparing for other experiments of the expedition. So it hap- 

 pened that the director spent several weeks on Mount Wilson at 

 instrument making and was not quite ready to begin the ozone ob- 

 servations in 1923. 



The second object was to test new improvements on the solar 

 cooker. By the lively interest of Director Stratton, the Bureau of 

 Standards had constructed by their skillful glass blower, Mr. Sperl- 

 ing, a long, pyrex-glass, double-walled vacuum tube to inclose the 

 heater tube of the Mount Wilson solar cooker. As stated in Volume 

 IV of the Annals of the Astrophysical Observatory, nearly nine- 

 tenths of the loss of heat had hitherto occurred from the heater tube 

 within the great mirror. It was to check this loss that the new 

 device was planned. 



Unfortunately, the aluminum of the mirror was found much de- 

 teriorated and could not be fully restored by polishing. Hence the 

 mirror was very inefficient in 1923. Nevertheless, the vacuum tube 

 showed its efficiency by the fact of the heating of the oven to 175° C, 

 or fully 2.5° C above the usual maximum temperatures of 1920. 

 But new troubles arose. The oil circulation became leaky at the new 

 high temperature, spontaneous combustion of the cotton heat insu- 

 lation occurred, and the experiments had to be stopped after long- 

 continued vain attempts to close the leaks by soldering. Also the 

 vacuum tube, which was really made too long for safety, soon broke 

 un,der the unequal heating strains. After this breakage occurred 

 the maximum temperatures attained were but 120° C, showing that 

 over 50° C. of advantage came from the employment of the vacuum 

 device. The experiments seemed so promising that a continuation 

 of them was arranged for 1924, and new and improved instrumental 

 constructions were prepared by Mr. Kramer during the winter 

 months 



The third piece of work attempted was with the 100-inch tele- 

 scope on the energy spectrum of the brighter stars. Messrs. Abbot 

 and Aldrich had, indeed, done this with moderate success in 1922, 

 employing the vacuum bolometer and galvanometer. But great 

 trouble had been found in the use of those instruments at extreme 

 sensibility. Fortunately, the late Dr. E. F. Nichols had offered to 

 have prepared a radiometer of improved design for the work. This 

 instrument, constructed by Dr. J. D. Tear, proved equally as sensitive 

 as the bolometer used in 1922, and practically as easy to use as a 

 meter stick. 



