PHYSICS OF THE GLOBE. G9 



CONSTITUTION AND PROPERTIES OF THE AIR. 



Mr. G. W. Hill, of Nyack, New York, contributes to the 

 July number of t\\Q Analyst a paper on an empirical formula 

 for the volume of atmospheric air at any temperature and 

 pressure. Starting with the fundamental assumptions (1) 

 that under constant pressure the ratio of volume to temper- 

 ature is constant, and (2) that the constant ratio is itself a 

 function of the pressure, he shows that Regnault's observa- 

 tions of the volume and tension of air, intended as a test of 

 the law of Boyle and Mariotte, lead to the conclusion that 

 this law is exactly true only at the temperature of 130 C, 

 and that the coefficient of expansion under a constant press- 

 ure is 0.0036445 at a pressure of zero, whence it increases 

 up to 0.0038618 at a barometric pressure of 21.5 meters, or 

 about twenty-eight atmospheres. 



The carbonic-acid gas in the atmosphere has been observed 

 by Farsky at Tabor in Bohemia, altitude 1400 feet. Daily 

 observations for one year gave a mean value of 3.43 vol- 

 umes in 10,000, or 0.034 per cent. The quantity of this gas 

 increased with the variability of the weather. 



Winkelmann shows that observations lend probability to 

 the theoretical conclusions of Von Obermayer that the co- 

 efficients of conduction for heat of air and hydrogen have 

 different and not the same ratios at different temperatures. 

 Similarly Von Obermayer has shown that the coefficient of 

 friction for hydrogen increases with the temperature more 

 slowly than does that for the air. These results are con- 

 firmed by a more recent investigation by Pulitz. 



The absorption of radiant heat by aqueous vapor has been 

 treated of very well by Haga, who reviews the work of Hoor- 

 weg, and concludes that a column of saturated air at 17 or 

 18 C, one meter long, absorbs 3 per cent. ; 3.3 meters long, 

 10 per cent, of the heat radiated from a Leslie cube at 100 C. 

 Besides these, Buff, of Giessen, has also shown that aqueous 

 .vapor is far more, and dry air far less, diathermanous than 

 was maintained by Tyndall. Their results materially effect 

 some meteorological theories. 



Lins shows how observations of halos may be utilized to 

 determine the dew-point at high elevations in the air. 



Kummer has, in the Berlin Abliandlungen, continued his 

 investigations into the resistance of air to projectiles. 



