SUN'S HEAT ABBOT. 



155 



or beans upon the floor of the great barn, and I had imagined Boaz 

 as going out to sleep upon his barn floor and wondered why he pre- 

 ferred doing so to sleeping in the house. Our experience in Algeria 

 solved this mystery, for it appeared that the threshing floor was 

 a hard level place upon the ground where Boaz slept under the 

 light of the stars. The reason why he did so was doubtless the same 

 that induced our French neighbor to take his double-barreled shotgun 

 and his dog and go out and sleep on his grain pile, with the dog tied to 

 his ankle — to prevent his neighbors from stealing the grain. Many 

 other sights and customs reminded one continually of passages in the 

 Bible, among them especially the driving of the oxen round and 

 round upon the wheat to tread out the grain. As they took a mouth- 

 ful now and then, one remembered that it says in the law: "Thou 

 shalt not muzzle the ox when he treadeth out the corn." 



Unfortunately the year 1911 proved to be a little unfavorable to the 

 comparison of results between Algeria and California, owing to the 

 unusual prevalence of cirrus clouds at both stations. Although the 

 results appeared to support the view of the sun's variability, they 



Fig. 2. — Brightness distribution along sun's diameter for different colors. 



were not wholly conclusive and the expedition to Algeria was re- 

 newed in June, 1912. 



We were still pursued by unfortunate circumstances as far as in- 

 vestigating the variability of the sun was concerned, for the great 

 volcanic eruption of Mount Katmai, in Alaska, which took place 

 about June 6, filled the atmosphere of the whole northern hemisphere 

 with volcanic dust, which spread to Algeria and California within 

 less than three weeks after the eruption, and, growing more and more 

 abundant, so much obscured the sun's rays that a falling off of 20 per 

 cent of their intensity at midday was found not unusually the case in 

 July and August, 1912. Notwithstanding these untoward circum- 

 stances, the results of 1912 taken in combination with those of 1911, 

 strongly confirmed the reality of the variation of the sun — so much so 

 that thereafter we had no doubt of the reality of this discovery. 



SOME DEVELOPMENTS OF THE RESEARCH IN THE INTERVAL BETWEEN THE 

 ALGERIAN AND SOUTH AMERICAN EXPEDITIONS. 



The matter received a further confirmation, however, in 1913, 

 by the introduction on Mount Wilson of the tower telescope and the 

 investigation of the distribution of radiation over the sun's disk. 



