38 PHOTOSYNTHESIS 



Without entering here upon a discussion of this theory, it is nevertheless 

 well to bear in mind that the older analyses were carried out by means of 

 different methods and at a time when all the precautions essential for 

 accurate air analyses were not yet realized. 



Lundegardh,'* working on the island of Hollands Vadero, 3.2 kilo- 

 meters from the mainland of Sweden, reported the following analyses for 

 carbon dioxide during the summer months : 



1920 1921 1922 1923 



612 0.5603 0.5267 0.5565 mg. per Liter 



03295 0.03031 0.02843 0.0300 vol. per cent 



19.97 17.3 16.48 15.39 mean temperature 



The mean variation during any one summer was ± 14 to ±16 per cent. 

 That there is a variation in the COo-concentration during day and 

 night has been reported by a number of investigators. Thus Reiset,^'' 

 M^unz and Aubin,-'^ and Letts and Blake ^' conclude that the diurnal CO2 

 content is about 12 per cent lower than the nocturnal when the analyses 

 were made at some distance from the sea. Such variations were not ob- 

 served in analyses made at sea (Thorpe) ^^ or on a small island (Lunde- 



gardh).^^ 



Schulz ^° reports variations ranging in extremes from 2.7 to 3.2 m 

 the air over the North Sea and Baltic. He considers these as due to in- 

 accuracies in analyses rather than actual differences in the carbon dioxide 

 content of the atmosphere and regards a mean value of 0.000293 at- 

 mosphere as the partial pressure of carbon dioxide over these bodies of 



water. 



The entire question of the carbon dioxide content of the atmosphere 

 is in need of a thorough investigation with uniform methods at different 

 points on the earth and extending over a number of years. It is only in 

 this way that a solution of such questions as convection, the complete mix- 

 ing of the atmosphere and the influence of land and sea is to be hoped 

 for. KendalL'^ concludes his discussion of the carbon dioxide content 

 of the atmosphere with the following comment : "The fact that exceed- 

 ingly large variations (as much as 700 per cent) have been recorded by 

 numerous observers is probably due to the faulty methods of estimation 

 that have been generally employed. The most careful and recent analyses 

 of pure out-door air indicate relatively constant values. Unfortunately 

 most of the observations on record have been obtained in connection with 

 non-chemical investigations, and these frequently betray the fact that at 



"* Lundegardh H., Der Kreislauf der Kohlensaure in der Natur. Jena, 1924, p. 9. 

 *»Reiset, J. a'., Compt. rend., 88, 1007 (1879). 



"Mirnz A., aAd Atibin, E.. Compt. rend., 92, 247, 1229 (1881), 93, 797 (1881), 

 94, 1651 (1882), 96, 1793 (1883). 



"Letts and Blake, Roy. Soc. Dublin Proc. N. S., 9, 107 (1899-1902). 



''Thorpe, Ann. Chem., 145, 94 (1868). 



" Lundegardh, I.e., p. 16. 



»" Schulz, Arch, deutsch. Seewarte, 40, 16 (1922), 41, 6 (1923). 



"Kendall, J., Jour. Amer. Chem. Soc, 38, 1490 (1916). 



