PLANT WORLD FOB Jl 1 V, 1919, w IS tSSI i D JANUARY 7. 



SUNLIGHT AND ITS MEASUREMENT 



HOWARD E. PULLING 



The Johns Hopkins University, Baltimore, Maryland 



II. MEASUREMENT OF SOLAR RADIATION 



It is plain from the foregoing data that sunlight is not even 

 approximately an invariant constant either in quantity or 

 quality at any station of observation on the earth's surface. 

 It follows that for biological experimentation in which it is 

 desired to ascertain the influence of radiation, resort must be 

 had to artificial illuminants, appropriately controlled, or else 

 the incoming radiant energy must be constantly measured. 



It is not a part of the plan of this paper to enter into a dis- 

 cussion of artificial illuminants although for those interested a 

 bibliography that seems to be sufficiently extensive to meet 

 the initial needs of biologists is included. 35 It may, however, 

 be noted that the behavior of the more recent types of electric 



35 Pirani, M. von, and A. R. Meyer, tlber die neueren elektrishen Gli'ih- 

 lampen mit Gasfiillung. Elektrotech. Z. 36: 493-496; 507-510. 1915. 



Mey, K., Die Nitralampe der Allgemeinen Elektricitats Gesellschaft. Eleck- 

 trotech. Z. 36: 376-377. 1915. 



Middlekauff, G. W., and J. F. Skogland, The photometry of gas filled lamps. 

 U. S. Bur. Standards Sci. paper 264: 587-604. 1916. 



Robinson, R. C, Candle power measurements of a series of gas filled in- 

 candescent tungsten lamps. Trans. Ilium. Eng. Soc. 11: 187-191. 1916. 



Tuck, D. H., Photometry of gas filled tungsten lamps. Elec. World 65: 

 78. 1915. 



Mackay, G. M. J., The characteristics of gas filled lamps. Trans. Ilium. 

 Eng. Soc. 9: 775-794. 1914. 



Hulburt, E. O., The emissive power of tungsten for short wave lengths. 

 Astrophys. J. 45: 149-163. 1917. 



Rolinson, W. H., New types of incandescent lamps and their relation to the 

 street lighting problem. Trans. Ilium. Eng. Soc. 11: 269-281. 1916. 



Merrill, G. S., Incandescent lamp developments. Trans. Ilium. Eng. Soc. 

 11: 525-538. 1916. 



Other references will be found scattered through the remainder of the paper. 



187 



THK PLANT WORLD, VOL. 22, NO. 7 

 JULY, 1919 



