IV PREFACE 



In the present discussion the results of the balloon flights and 

 spectrobolometric work are not incorporated. A more detailed study 

 of the atmospheric radiation, in which these valuable data would be 

 indispensable, may be undertaken more profitably after a determina- 

 tion shall have been made of the individual atmospheric transmission 

 coefficients throughout the spectrum of long wave rays as depending 

 on humidity. This study is now in progress by Fowle and others, 

 and the results of it doubtless will soon be available. 



Anders Angstrom. 

 Upsala, Sweden, 



December, 19 14. 



