METEOROLOGY. 375 



lines, but in very moist weather they sbow strong absoption bands, ^vhi( li 

 are more numerons and darker as the relative humidity of the air is 

 greater. These demonstrate that this absorption is not due to the true 

 aqueous vapor in the air, but to water in a fluid condition, namely, mi- 

 nute fog" or cloud parti(;les. lie also concludes that it is certainly 

 water in this fluid condition that causes the deep blue of the sky, since 

 no other ground can be imagined why the color should be a deeper blue 

 in moister weather; this view is also confirmed by the fact that in as- 

 cending high mountains the tint changes from a dark to a black blue. 

 [Z. O. G. i¥., XVIII, p. 27G.) 



374. Captain Abney and Colonel Festing have presented a valuable 

 pai)er on the influence of water in the atmosphere on the solar spec- 

 trum. They both recognize the fact that the spectrum extends to the 

 lower limit established byLangley; they then investigate the radiation 

 from the positive pole of the electric arc, and introduce absorbing layers 

 of water. These so modify the original curve of distribution of heat 

 in the spectrum that even the introduction of an absorbing layer of 

 water 1^ of inch thick reduces it to similaritj" with the curve given by 

 sunlight, whence they conclude that the greater part of the absorption 

 in the red and ultra red portions of the solar spectrum is due to the 

 presence of water. As opposed to Langley's opinion that the maximum 

 intensity of the solar spectrum outside of the earth's atmosphere lies 

 nearer the blue, their own observations give an extra-atmospheric curve 

 having a second maximum in the ultra-red. This they explain as due to 

 the superposition of radiations belonging to a low temperature upon 

 radiations from bodies with a high temj^erature, the former being the 

 prevalent. By examples they show that the superposition of such 

 curves from different sources of heat will give such a result. Assuming 

 with Dewarthat the areas of these radiation curves are proi)ortional to 

 the temperatures of the radiating bodies, they find the temperature of 

 the sun\s surface to be between 10,000 and 12,000 degrees. (Z. 0. G. M., 

 XIX, 430, and Nature, xxviii, p. 45.) 



375. H. Becquerel has studied the same question by means of the 

 phenomena of phosphorescence. He has investigated under different 

 atmospheric conditions the ultra-red part of the spectrum, and, like 

 (kiptain Abney, found that the absorption lines increase with the rela- 

 tive humidity. He also found that the absorption bands of layers of 

 fluid water agreed for various thicknesses of water with the above lines 

 for corresponding relative humidities. {Z. 0. G. M., xviii, ]). 277.) 



376. Cornu proposes to determine the absorption of the solar rays by 

 observing the intensity of well determined atmospheric lines in the 

 solar spectrum, which he accomplishes by comparing them with the 

 constant lines that certainly owe their existence to the absori)ti()n in the 

 solar atmosphere. This is an extension of the proposition to observe 

 the rain l)an<l so earnestly advocated by IMazzi Smyth. Cornu chooses 

 that portion of the spectrum between the wave length 587.40 and 002.90, 



