NO. 19 THE SILVER DISK PYRHELIOMETER — ABBOT 7 



15. (Note.) The approximate method of procedure stated in (12) 

 and (14) is much easier than the exact method, and having been 

 found by experiments to yield closely comparable results under all 

 circumstances of use, within the error of measurement, it has been 

 adopted, and the standardization of the instrument is made by this 

 method. 



16. To reduce the results R\ and R\ to standard calories per 

 square centimeter per minute, or to the scale provisionally used up 

 to 1910 by the Smithsonian Institution, multiply by the factors fur- 

 nished from the Smithsonian Institution with each instrument. 



17. Under favorable circumstances an experienced observer can 

 read to a probable error of ^ per cent for a single reading. The 

 sample readings here given differ more than this, for they were 

 made at sealevel with variable sky. 



