348 



SCIENCE 



[N. S. Vol. XXXIX. No. 1001 



long as we observe at the earth's surface, 

 no matter how high the mountain top on 

 which we stand, the atmosphere remains 

 above us, and some estimate must be made 

 of its transmission before the solar con- 

 stant can be determined. Different per- 

 sons will differ in the degree of confidence 

 which they will ascribe to measurements 

 of the atmospheric transmission, such as 

 have been considered, and there are still 

 some who totally disbelieve in the accu- 

 racy of the results thus far obtained, even 

 though they be confirmed by observations 

 at such differing altitudes. Accordingly 

 it has seemed highly desirable to check the 

 results by a method of direct observation 

 by the pyrheliometer, attaching the instru- 

 ment for this purpose to a balloon and 

 sending it to the very highest possible alti- 

 tudes. By a cooperation between the 

 Smithsonian Institution and the United 

 States Weather Bureau, experiments for 

 this purpose were made in July and Au- 

 gust of the year 1913. 



The instruments employed were modified 

 in form from the silver-disk pyrheliometer, 

 which has been described above. As the 

 apparatus could not be pointed at the sun 

 the disk was placed horizontally, and the 

 thermometer was contrived to record its 

 temperature by photography upon a mov- 

 ing drum. The receiving disk was alter- 

 nately exposed to the sun and shaded by 

 the intervention of a shutter, operated in- 

 termittently by the clock work which 

 rotated the drum under the stem of the 

 thermometer. Five instruments of this 

 kind were sent up on successive days. 

 While it was well known that the tem- 

 perature of the higher air would go as low 

 as — 55° C, it was believed that a black- 

 ened disk exposed half the time to the 

 direct sun rays, would certainly remain 

 above the temperature of — 40°, which is 

 the freezing point of mercury. This expec- 



tation was disappointed. Accordingly, 

 owing to the freezing of the mercury in 

 the thermometer, the highest solar radia- 

 tion records obtained during the expedition 

 were at the altitude of 13,000 meters, al- 

 though the balloons in some instances 

 reached the altitude of 33,000 meters. 



The results obtained, while they have 

 not the same degree of acciiracy as those 

 obtained by direct reading of the silver 

 disk pyrheliometer, are yet of considerable 

 weight. All the measurements unite in 

 indicating values of the solar radiation at 

 altitudes of 10,000 meters and higher, 

 which fall below the value of the solar con- 

 stant of radiation as obtained by other' 

 methods, and above the value of the radia- 

 tion at the summit of Mount Whitney as 

 obtained by different observers with pyr- 

 heliometers. It is expected in the coming 

 year to repeat the observations with bal- 

 loons under much improved circumstances. 

 By aid of electrical heating apparatus it is 

 expected to keep the surroundings of the 

 disks at approximately the freezing tem- 

 perature, even though exposed to the air at 

 temperatures as low as — 55° C. In this 

 way it is hoped to obtain good pyrheliom- 

 eter measurements as high as it is possible 

 for sounding balloons to go, and possibly 

 to an altitude of 40,000 meters. As the 

 atmospheric pressure at such altitudes is 

 less than 1 per cent, of that prevailing at 

 sea level, the experiments, if successful, 

 may be expected to remove reasonable 

 doubt of the value of the solar constant of 

 radiation. 



C. G. Abbot 



SETH CABLO CHANDLEB 

 Dr. Seth Carlo Chandler, eminent astron- 

 omer, died on December 31, 1913, in his sixty- 

 seventh year after a short attack of pneu- 

 monia. 



Born at Boston, Mass., September 17, 1846, 



