66 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 



and used as the site for an observatory. The reservation was in fact made, 

 but no observatory has been established there. Mr. Abbot carried with him 

 to Mount Whitney a pyrheliometer and wet and dry thermometers, and made 

 observations on the summit both in the afternoon and morning hours. Both 

 he and Mr. Campbell were favorably impressed with the advantages of the place 

 for observing, and with the relative convenience of ascending the mountain, 

 considering its great altitude. Fine building stone, sand, and water were found 

 at the summit. Messrs. Campbell and Abbot, therefore, recommended to the 

 Secretary of the Smithsonian Institution that a grant from the Hodgkins fund 

 should be made for the purpose of erecting on the summit of Mount Whitney 

 a stone and steel house to shelter observers who might apply to the Institution 

 for the use of the house to promote investigations in any branch of science. 

 This recommendation was approved, and the house is now in course of con- 

 struction (July, 1909). 



It has been held by some astronomers that measurements of the " solar 

 constant of radiation " by high and low sun observations from a single station 

 at a low altitude, or even at the altitude of Mount Wilson, are subject to a 

 great error by reason of the impossibility of correctly allowing for loss in our 

 atmosphere. In order to ascertain if this objection is well founded, an expe- 

 dition to Mount Whitney by Mr. Abbot is planned for August, 1909. He will 

 carry a complete spectro-bolometric outfit, for which Mr. Kramer has con- 

 structed the mechanical parts in the shop of the Astrophysical Observatory at 

 Washington. This apparatus will point directly at the sun, so as to dispense 

 with reflections at a coelostat. A quartz prism and two magnalium mirrors 

 constitute the sole optical parts of the spectroscope, as it will generally be 

 used, but a glass prism and silvered mirrors will also be employed in the 

 examination of the water vapor bands and of the infra-red spectrum. With 

 the quartz and magnalium outfit it is expected to measure the energy of the 

 spectrum from about wave-length 0.30/* in the ultra-violet to wave-length 4m 

 in the infra-red. Simultaneously with these " solar constant " measurements 

 on Mount Whitney complete observations of the same kind will be made on 

 Mount Wilson by Doctor Ingersoll, and if the results of the two shall agree it 

 is thought that there will be left no ground for reasonable doubt of the accuracy 

 of the method. 



SUMMARY. 



The principal work of the year comprises frequent spectro-bolometric exam- 

 inations of the relative brightness of different parts of the sun's disk for rays of 

 several different wave lengths; measurements of the transmission of long-wave 

 rays, such as the earth emits, through very long columns of moist air; the 

 steady continuation of the reduction of Mount Wilson and Washington observa- 

 tions; six months of almost daily observation on Mount Wilson for the deter- 

 mination of the variability of the sun ; a preliminary observing expedition to the 

 summit of Mount Whitney; and the complete preparation of apparatus and ar- 

 rangements for a series of observations of the " solar constant " by the spectro- 

 bolometric method, to be made simultaneously at Mount Wilson and Mount 

 Whitney in August, 1909. 



Respectfully submitted. 



C. G. Abbot, Director. 



Dr. Charles D. Walcott, 



Secretary of the Smithsonian Institution. 



