F. W. Very — Transmission of Terrestrial Radiation. 521 



Angstrom, is of quite minor importance. He assigns to "the 

 remaining 0'09 gr. cal. which probably are transmitted through 

 the lower absorbing layers " (meaning by this the entire rem- 

 nant of nocturnal radiation, since, of the original 0*15 of this 

 illustration, - 06 gr. cal. are supposed by him to be stopped at 

 3000 m.) a further absorption by "ozone in the higher and 

 colder strata of the atmosphere," amounting in winter to 50 

 per cent, and on the average to 20 per cent. The ozone band 

 between 9 and 10/^, discovered by Professor Knut Angstrom, 

 sometimes exerts an absorption of 50 per cent in winter, but 

 within the limits of the band only. It is not correct to apply 

 this value of the percentage of absorption, within a limited 

 range of wave-length, to the entire remnant left from aqueous 

 absorption which extends through many times this range. 

 This is not the first time that similar elementary considerations 

 have been pointed out, but since they are frequently over- 

 looked as in the present instance, it is necessary to emphasize 

 them. My measures show that, in winter, between 3*00 and 

 3 - 72 per cent of the entire remnant of the spectrum beyond 

 great E, left after aqueous absorption, may be absorbed by 

 ozone, and much less in summer, the remaining radiation, over 

 96 per cent, falling outside the limits of the ozone band. Com- 

 pared with water vapor and its products, the hydrols, all other 

 atmospheric absorbents are nearly negligible. 



Taking the extremes of the range of terrestrial radiation 



(K =f~? — ^—) as influenced by aqueous vapor (pressure of 

 vapor in mm. = a), we have : 



Angstrom 



a = 3-50 to 4-50, 



R = 0-198 



(t 



a = 11-90 " 13-24, 



R = 0-146 



Very (Winter) 



a = 0-63 " 2-39, 



R = 0-222 



" (Summer) 



a = 9-14 " 12-67, 



R = 0-149 



Horn en 



R = 0-22 " 0-13. 





These results being in good agreement, and since the afore- 

 said lunar observation definitely confirms the larger values of 

 the transmission of terrestrial radiation deduced for middle 

 latitudes by the method advocated in this paper, we may con- 

 clude that with the clearest skies and in middle latitudes, trans- 

 missions of about 26 per cent are common in summer and 

 upwards of 58 per cent in winter. 



Westwood Astrophysical Observatory, 

 Westwood, Massachusetts. 



A.M. Jour. Sci. — Fourth Series, Vol. XLI, No. 246. — June, 1916. 

 36 



