METEOROLOGY AND ALLIED SUBJECTS. 267 



effect in absorbing rays of heat than has pure dry air. {Z. 0. G. M., 

 Vol. XVI, 1881, p. 37.) 



The question of the absoq^tion of the sohir heat by atmospheric aque- 

 ous vai)or has been further supplemented by the studies of Lecher into 

 the absorption of carbonic-acid gas; he finds that a column 1.05"' long 

 at ordinary pressures and temperatures absorbs 13 per cent, of the heat 

 that reaches the earth's surface when the sun is at its maximum height. 

 (For Vienna this is about 70° above the sun's horizon.) Th's absorp- 

 tion of the solar rays diminishes very rapidly as the sun sinks toward 

 the horizon, whence it follows that the CO2. in the atmosphere itself 

 absorbs the radiation in proportion to the length of the path of the ray, 

 and that the total CO2. in the atmosphere (which is equivalent to a layer 

 2.4™ thick at ordinary pressures and temperatures), is sufficient to ex- 

 plain the whole absorption of solar heat, which is about 2G per cent, as 

 shown by Pouillet, or 40 per cent, according to Forbes. {Z. 0. G. JT., 

 XVI, 1881, p. 271.) 



V. — SOLAR RADIATION AND TERRESTRIAL TEMPERATURE. 



In some remarks on the theory of the general atmospheric circula- 

 tion Hann says the area of the earth's STirface between the equator and 

 30^ latitude is as great as the entire remaining portion of the hemi- 

 sphere up to the pole (2,308 thousand square miles against 2,323 thou- 

 sand). The surface of the zone between the tropics and the 45th parallel 

 is still considerably greater than that of the entire area from 45^ to the 

 pole (1,427 thousaud square miles against 1,384 thousand). The area 

 of the zone from 30 to 40 degrees alone is greater than the entire cir- 

 cumi^olar region from the pole to GO^ latitude (G61 thousand square 

 miles against G25 thousand). That is to say, that when, for instance, 

 the region from 30^ to the equator receives in one year an excess of heat 

 of several degrees, this will bring about the outflow overhead of a mass 

 of air that is sufficient to uniformly cover the region from 30° to the 

 pole. 



If the air in the zone from the tro]>ics to the 45th parallel is abnormally 

 warmed, then this can have an influence upon tlie temperature and the 

 weather of the entire portion of the hemisphere lying north thereof up to 

 the Pole, for the upper currents have only this way to flow off, because the 

 gradient in the upper regions prescribes this path. If, therefore, we ob- 

 serve an uncommonly high barometric pressure over Europe and the con- 

 tiguous pori ions of the Atlantic Ocean for a long time continuously, then 

 the cause thereof is probably to be found in a previous excess of heat 

 communicated in lower latitudes far beyond the limits of the synoi)tio 

 chart. Observations of atmospheric pressure at high altitudes of the 

 subtropic and tropical zones will i^robably give us important conclu- 

 sions as to the cause of the variable intensity of the upper currents. It 

 is just as important to know the distribution of atmos])heri(! pressure in 

 the upper regions of the air as to know the distribution on the surface of 



