REPORT OF THE SECKETAEY. 103 



and accurate determination of the solar variation for comparison 

 with climatic changes. Measurements of the transmission of long- 

 wave rays through long columns of moist air are almost ready for 

 publication and appear to be resulting very satisfactorily. A new 

 instrument, called the pyranometer, for measuring skylight and 

 nocturnal radiation has been tested and found accurate. 

 Eespectfully submitted. 



C. G. Abbot, 

 Director Astrophysical Observatory. 

 Dr. C. D. Walcott, 



Secretary of the Smithsonian Institution. 



