February 18, 1916] 



SCIENCE 



241 



shine "^ Mr. Very hangs the merit of his work 

 on the exceptional clearness of August 8 and 

 9, 1912. It is very singular that these exception- 

 ally clear days occurred when the effects of the 

 dust cloud from Katmai volcano were at their 

 maximum. At various high altitude stations 

 the direct sunlight at high sun was reported fo 

 be reduced in August from 10 to 20 per cent., 

 and skylight near the sun in daytime notably 

 increased, yet it is at this very time that the 

 moonlight scattered by the sky near the moon 

 was so exceptionally small at Flagstaff.' 



Thirdly. Mr. Very, in his paper submitted 

 at Berkeley,* argues a high transparency of 

 the atmosphere for the escape of terrestrial 

 radiation, as opposed to the conclusion of Mr. 

 A. Angstrijm. Very states " that practically 

 all the terrestrial radiation which the atmos- 

 phere is capable of absorbing disappears in 

 the first few meters of air traversed by the 

 rays " and hence " the observed nocturnal 

 radiation is a radiation to space," contrary to 

 the opinion of Mr. A. Angstrom that only a 

 fraction of it is a radiation to space. 



The phenomenon is as follows : A blackened 

 surface at 20° C. is found to give off radiation 

 at a rate of from 0.12 to 0.20 calories per 

 square centimeter per minute when exposed to 

 cloudless night sky. Such a surface would 

 radiate about 0.55 calories if exposed to an en- 

 closure at absolute zero. The question is : 

 Does the nocturnal radiation observed (0.12 to 

 0.20 calories) represent radiation transmitted 

 almost wholly to space, or is it in a large de- 



2 See Astronomisdhe NacJirichten, Nos. 4,819-20, 

 1915. 



3 See in this connection Kimball, ' ' The Effect 

 Upon Atmospheric Transparency of the Eruption 

 of Katmai Volcano," Monthly Weather Review, 

 1913, 41: 153-159, also, "Volcanoes and CU- 

 mate, " by Abbot and Eowle, Smithsonian Miscel- 

 laneous Collections, Volume 60, No. 29, 1913; also 

 Kimball, Monthly Weather Beview, September, 

 1915, p. 442, in which he shows for Santa F6, New 

 Mexico, elevation 7,000 feet, that as late as the 

 last half of October, 1912, the mean solar radia- 

 tion was only 1.37 calories at 3 = 48°, whereas he 

 obtained 1.53 calories as the mean for the corre- 

 sponding period of 1914. 



* See Pop. Ast., Vol. 23, p. 648. 



gree representing merely the radiation of the 

 surface outward minus the radiation of the 

 atmosphere inward ? Mr. Very claims that for 

 wave-lengths at which the atmosphere can ab- 

 sorb the rays, its full absorptive effect is pro- 

 duced within a few meters of the radiating 

 surface. Here the temperature is not mate- 

 rially different from that of the surface, and 

 re-radiation of the atmosphere in these wave- 

 lengths approximates that of the black surface 

 according to his view. Mr. Angstrom, on the 

 other hand, believes that many of the absorb- 

 able rays penetrate far into the atmosphere, 

 where the temperature becomes much reduced, 

 and hence the re-radiation is less than the out- 

 going radiation because it comes from a source 

 at lower average temperature. 



The point at issue is solved if it can be 

 shown that increased length of path, or in- 

 creased atmospheric humidity, do or do not 

 affect nocturnal radiation. For the evidence 

 see Table IX., p. 63, of A. Angstrom's paper, 

 "A Study of the Eadiation of the Atmos- 

 phere," Smithsonian Miscellaneous Collec- 

 tions, Vol. 65, ISTo. 3. Experiments were made 

 at two stations on the radiation to small parts 

 of the sky at different zenith distances. I refer 

 particularly to observations at Bassour, 

 Algeria, although Mt. Whitney observations 

 support the following conclusions too. Length 

 of path in the atmosphere is shown to be of 

 decided effect. The change from air mass 1 to 

 air mass 3 reduced nocturnal radiation on 

 August 20, 1912, by more than YO per cent. 

 The result also depends on the degree of 

 humidity prevailing, as is shown plainly by in- 

 spection of the whole table. These results 

 show that the whole vertical thickness of the 

 atmosphere is insufficent to absorb " practically 

 all the terrestrial radiation which the atmos- 

 phere is capable of absorbing." 



C. G. Abbot 



UNIVERSITIES AND UNPREPAREDNESS 



To THE Editor of Science : Some weeks ago 

 an' open letter from Professor Stewart Baton 

 appeared in Science. It was entitled, " Uni- 

 versities and Unpreparedness." It suggested 

 that universities could play an important part 



