November 4, 1922] 



NA TURE 



609 



(1912-20)., but also at Calama in Chile (1918-20), is 

 given as 1-946. Dr. Abbot admits, however, a criti- 

 cism by Kron, to the effect that this value may be 2 

 per cent, too low owing to a systematic influence 

 tending to magnify the measured atmospheric trans- 

 missibility for ultra-violet rays. The error does not 

 affect the evidence for variability in the solar radiation. 



The above value is slightly greater than the mean 

 (1-933) f° r the epoch 1902-12, and it is suggested 

 that the increase is associated with the greater average 

 solar activity during the later period. Whether this 

 be so or not (and the more detailed comparison of values 

 of the solar constant with sunspot numbers scarcely 

 strengthens the evidence for such a connexion), the 

 really remarkable result is the minuteness of the 

 change ; the solar agent which affects the diurnal 

 variation of terrestrial magnetism must vary by 20 

 per cent, or more, instead of \ per cent, or 1 per cent., 

 as here. There is, of course, a very slight compensation 

 for any general increase of solar emissivity at times of 

 many sunspots, owing to the diminution of emitting 

 surface caused by the presence of the low-temperature 

 spots ; if there are also absorbing vapours above the 

 spots, the compensation may not be merely slight ; 

 an appreciable drop (about 5 per cent.) in the solar 

 constant coincided with the passage of a very large 

 group of sunspots across the sun's disc in March 1920. 



The short-period " solar-constant " variation, of 

 amount from 2 to 10 per cent., has been further con- 

 firmed by simultaneous observations at Mount Wilson 

 and at Calama, Chile ; these stations are about 5000 

 miles apart, on opposite sides of the equator, and at 

 different altitudes. Their observations show a moder- 

 ate degree of correlation (0-491). Attempts have been 

 made by Dr. Abbot and his colleagues to find con- 

 nexions between the variations of the solar constant 

 and the variations of contrast of brightness on the sun's 

 disc which have been revealed by observations of the 

 distribution of radiation over the sun's surface. Such 

 measures have been carried on now for more than eight 

 years by the Smithsonian observatory. The association 

 between the two phenomena, if real, is very complex, 

 high contrast sometimes accompanying high, and some- 

 times low, values of the solar constant. A correspond- 

 ingly complex theory is propounded to account for this, 

 but a much longer series of observations is required to 

 test the theory. Dr. Abbot urges the desirability of 

 other observatories taking up solar-constant work, 



especially in view of the possibility that variations of 

 radiation have predictable meteorological consequences, 

 as Clayton's studies might suggest. 



Various other cognate researches have been made by 

 Dr. Abbot and his colleagues, Messrs. Fowle, Aldrich, 

 Moore, and Abbot, during the period, since 1912, dealt 

 with in the volume of Annals before us. Variations in 

 the solar radiation have been tentatively sought by 

 observing the changing brightness of the planets. The 

 sun's total radiation has also been measured, at various 

 terrestrial altitudes, from sea-level to high mountain 

 stations, and beyond, up to 25,000 metres, by sounding 

 balloons. A new empirical method of determining the 

 solar constant by observations occupying only fifteen 

 minutes in all has been introduced at Calama ; this 

 removes one of the chief sources of error in the longer 

 method, namely, real variations in atmospheric trans- 

 parency during the observations. In the new method 

 the amount and character of the atmospheric absorp- 

 tion at the time of a pyrheliometer observation is 

 inferred from a measure of the brightness of the sky 

 in a zone 15 from the sun, and from the intensity of a 

 particular water absorption band observed by means of 

 the holograph. Many observations of the brightness 

 and transmissive power of the atmosphere have been 

 made in the course of this and the other parts of the 

 solar-constant work. Laboratory studies have been 

 made on the absorption of long-wave radiation by 

 water vapour, carbon dioxide, ozone, and by many 

 common solid substances. The reflecting power of 

 clouds has been measured by balloon observations at 

 Mount Wilson in 1918 ; the ratio of reflection found was 

 78 per cent., independent of the solar altitude. From 

 this the albedo of the earth is estimated at 43 per 

 cent. 



On account of over-frequent cloud and haze at 

 Mount Wilson the solar-constant work carried on there 

 since 1915 has been transferred to Mount Harqua Hala 

 in Arizona, and the Calama station in the plain has been 

 removed to Mount Montezuma, a few miles away. For 

 a short time in 1917-18 observations were made at 

 Hump Mountain in North Carolina, but the situation 

 proved too cloudy. It is interesting to note, however, 

 that one excellent observation was made at a lower 

 air temperature than any experienced elsewhere during 

 a complete solar-constant observation ; both the hands 

 and feet of the observer with the pyrheliometer were 

 frozen in the course of the measurements ! 



Obituary. 



W. H. Wesley. 



WILLIAM HENRY WESLEY, who died on 

 October 17, at the age of eighty-one years, 

 was appointed assistant secretary of the Royal 

 Astronomical Society in 1875, and continued in that 

 office till his death, a period of forty-seven years. 

 He had excellent qualifications for the post, being 

 most orderly and methodical in all secretarial and 

 editorial work, and having great skill as a draughts- 

 man and engraver, as was exemplified in his en- 

 gravings of Dr. Boeddicker's drawings of the Milky 



NO. 2/66, VOL. I 10] 



Way, and the illustrations of the corona in Mr. Ran- 

 yard's memoir on solar eclipses. It used to be said 

 that Wesley knew the corona better than any man 

 living, although he had never seen it; however, 

 after an unsuccessful effort in Norway in 1896, the 

 equatorial coudi at Algiers was put at his service 

 by M. Trepied in 1900, when he made a detailed 

 drawing in the short duration of totality (64 seconds) 

 and expressed his opinion that the eye was no more 

 efficient than the photographic plate for this work. 

 He made combination drawings from the negatives 

 obtained bv the Greenwich staff in the eclipses of 1898, 



