410 SCIENTIFIC RECORD FOR 1882. 



yellow, green, and red skies, wliicli form sucli a large portion of all 

 weatlier lore, but witliout decisive results, for sunset spectra are too 

 complicated and too fleeting to be unraveled by a small instrument. 

 They certainly seem to differ, but tlieir spectra are not so marked as 

 tlieir appearance to the naked eye. But even supposing that this idea 

 is completely verified, and that the spectroscope can be used as a new 

 weapon of research to discover the still unknown nature of clouds, and 

 that we should be able to say that such and such an absorption spectrum 

 belongs to such and such a kind of sky, there are no grounds for believ- 

 ing that we can ever regard these spectra otherwise than as a new set 

 of sky prognostics, or that as such they will be of more use in forecast- 

 ing than those already known. What the use of any prognostics is in 

 forecasting, and how they are related to synoptic charts, and how iso- 

 baric lines map out the shape of rain areas, are other sides of the great 

 l)roblem of weather forecasting which cannot be discussed here." {Na- 

 ture, XXV, p. 573.) 



Messrs. Lecher and Pernter have studied the absori)tion of radiant heat 

 in gases and vapors. They consider " vapor-hesion" to have been an 

 important source of error in Tyndall's experiments. In their own 

 method the thermopile and the heat source were brought into the same 

 vessel. Air-currents were avoided by causing the surface of radiation 

 to be heated in each case suddenly from without, by means of a steam 

 jet, to 100^ C Among other results the absorption of water vapor is 

 found, in opposition to Tyndall, immeasurably small. Violle found on 

 Mont Blanc that a meter of the air absorbed only 007 per cent, of the 

 whole radiation ; according to this a layer of 300™ length would be 

 necessary to produce, with water vapor saturated at 12°, that absorp- 

 tion which Tyndall obtains in 1.22"". This and the author's own experi- 

 mental results are considered to i)rove beyond dispute the very small 

 absorption of aqueous vapor. The results for gases agree pretty well 

 with Tyndall's. Xo simple connection between absorption and pressure 

 of the substance was discoverable. The absorption, even for radiation 

 of a heat source of 100° C, is selective. The authors found the absorp- 

 tion of certain substances of the fat series examined to increase rapidly 

 with increasing proportion of carbon. It seems to be otherwise, how- 

 ever, with bodies from other groups; thus, e. g., benzole, notwithstanding 

 its six carbon-atoms, has a fairly small absorptive power. {Nature, 

 XXII, p. 543.) 



Dr. Lecher has made new observations, especially as to absorption of 

 solar radiation by the carbonic acid in the atmosphere. Experiments 

 with a gas lamp and a glass cylinder first showed that carbonic acid in 

 a length of 214™'^ gave passage to 94.8 per cent, of the radiation; 530™"', 

 93.8 per cent; 917"°, 89.0 per cent. At Greifenstein, outside of Vienna 

 (chosen for pure air), the sun's rays were also proved to undergo con- 

 siderable weakening in passages through carbonic-acid gas. A layer 

 of this gas 1 meter thick absorbed 13 per cent, when the sun had an 



