374 F. W. Very — Sky Radiation and Isothermal Layer. 



ozone must still suffer a corresponding destruction both by day 

 and by night through union with aqueous vapor to make 

 hydrogen peroxide. Traces of H 2 2 in rain water are greater 

 by day than by night, which lends support to the supposition 

 that there is increased formation of the peroxide in the 

 daylight hours. The production of H 2 2 by the sun's rays 

 has also been verified experimentally by Kernbaum.* But 

 granting the existence of a considerable quantity of ozone as a 

 permanent constituent of the upper air, and that this substance 

 must be included among the leading absorbents of telluric radi- 

 ation, taking its place with aqueous vapor and carbon dioxide, 

 and supplementing these substances in a region of the spectrum 

 where they are least effective, nevertheless ozone does not 

 appear to be the cause of the isothermal layer, for it contrib- 

 utes very little to the absorption of solar rays, while, on the 

 contrary, the absorption bands of aqueous vapor invade regions 

 of the spectrum where the solar rays have considerable power, 

 and finally the hydrols are potent near the very maximum of 

 the energy in the solar spectrum. 



The altitude at which the lowest limit of the isothermal layer 

 begins is determined by the amount of material in the lower air 

 suitable for absorbing terrestrial radiation and on the intensity 

 of this absorption. The commencement of the isothermal layer 

 is several thousand meters higher in the tropics than in Europe, 

 because the greater humidity of the tropical air makes it a 

 conservator of the atmospheric radiant potential up to an alti- 

 tude of about 15,000 m , as compared with 10,000 to 12,000 m for 

 the less moist air of the higher latitudes. On account of its 

 greater average elevation, the tropical isothermal layer has a 

 smaller average density, a smaller mass per unit of section, and 

 it absorbs less of the solar radiation. Hence its temperature is 

 a little lower than in Europe, since the accumulating power of 

 the layer is greatly aided by its enormous depth, and a lessen- 

 ing of the depth by several kilometers can not but have an 

 appreciable effect. 



Blairf inclines to the conclusion that, "in general, the pecu- 

 liarities in the temperature gradient up to and including the 

 upper or permanent inversion owe their existence to the influ- 

 ence of convection on the distribution of the constituents, 

 especially of the water of the atmosphere." Clayton, however, 

 attributes "a sudden fall of temperature which occurs after sun- 

 rise (about 9 a. m. in summer)" at a height of about 1000 meters, 

 to the cooling by expansion of ascending bodies of air, forming 

 part of the low-level convection system, and carried upward 

 by their momentum beyond the point of equilibrium. J; This 



* Bulletin Internat. Akad. Sci. Cracovie, 1911, p. 583. \ Op. cit., p. 212. 

 % "The Diurnal and Annual Periods of Temperature," etc., Annals Harvard 

 Observatory, vol. lviii, part 1, p. 18-19, 1904. 



