2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 52 



results of Simpson in this important field. Fowle ' carried on for 

 several years, 1908 to 1917, experiments on the absorption of radiation 

 of long wave lengths by the atmosphere contained in tubes of large 

 diameter and up to 800 ft. in length. These tubes were laden with 

 water vapor ranging from 0.2 up to 2.5 mm. of precipitable water, 

 and of carbon dioxide content ranging from 7 grams up to 160 grams 

 per meter cross-section at normal temperature and pressure. 



In his early experiments, Fowle had established means for deter- 

 mining the quantity of precipitable water in atmospheric air by means 

 of measurements on the bands pcrr, <^, and i(/ of the upper infra-red 

 solar spectrum. These experiments are fortunately very definite as 

 to the determination of water vapor equivalent to 0.3 mm. of pre- 

 cipitable water. 



In the summer of the years 1909 and 1910, Abbot observed the 

 infra-red solar spectrum from Mount Whitney, California, altitude 

 4,420 m. Holographs of the spectrum were obtained, having very 

 satisfactory quality as far as the delineation of the bands par, (f>, and j/' 

 is concerned.^ From these, Fowle determined the quantity of total 

 precipitable water in a vertical path of atmosphere above Mount 

 Whitney. On August 14, 1910, he observed 0.6 mm. Considering the 

 moderate altitude and the summer season, this small observed water- 

 vapor content hardly prepares one to accept Simpson's assumption 

 that the stratosphere, which begins at 12,000 m., and is at a tempera- 

 ture about 50° C. lower than that which prevailed at the summit of 

 Mount Whitney on that occasion, can contain half of the precipitable 

 water above that station. We have other evidence leading to the same 

 view. 



At Mount Montezuma, Chile, altitude 2,710 m., we have observed 

 spectroscopically the total precipitable water in a vertical column 

 above the station almost daily for about 10 years at all seasons. The 

 following table gives average values for the 12 months, and also 

 extreme values for each of these months, together with associated 

 surface temperatures. 



In illustration of the great alterations in the appearance of the solar 

 energy spectrum depending on the quantity of atmospheric humidity, 

 we give reproductions of two days' observations at Alontezuma, 

 plates I and 2. Note the bands par, <}>, if/ and fJ. 



* Fowle, F. E., Ann. Astrophys. Observ., Vol. 4, pp. 274-286. Astrophys. 

 Journ., Vol. 38, p. 393, 1913; Vol. 42, p. 394, 1915. Smithsonian Misc. Coll., 

 Vol. 68, No. 8, 1 91 7. 



^ See Annals, Vol. 4, fig. 50. 



