SOLAR RADIATION 



223 



Table 7. — Radiation Intexsities at Normal Incidence. — {Continued) 



Treurenberg, Spitzbergen * 



April . 



May. 



June. 



July. 



Sept. 



1.30 

 1.32 

 1.36 



1.19 

 1.14 

 1.21 

 1.22 

 1.19 



* Intensities are given in units of the Angetroni pyrheliometric scale. 



Table 8. — Solar-radiation Intensities on a Horizontal Surface 

 (Daily averages, gm. cal./day/cm.^) 



Month 



Jan . . . 

 Feb . . . 

 March . 

 April . . 

 May . . 

 June . . 

 July... 

 Aug... 

 Sept . . . 

 Oct . . . 

 Nov . . . 

 Dec . . . 

 Year . . 



Johannesburg,* 

 South Africa 



556 

 490 

 455 

 405 

 380 

 365 

 368 

 440 

 531 

 567 

 606 

 579 

 125.696 



Habana, 

 Cuba 



367 

 448 

 598 

 620 

 575 

 610 

 656 

 568 

 519 

 439 

 332 

 330 

 183,797 



Abisko,* 

 Sweden 



23 

 135 

 379 



463 

 468 

 366 

 228 

 143 

 51 

 7 



Green* 



Harbor, 



Spitzbergen 



2 

 59 

 273 

 457 

 546 

 363 



86 

 5 



Sveanor* 



407 



* Radiation intensities are believed to be recorded in units of the Angstrom pyrheliometric scale. 



time. Intensities at normal incidence are summarized in Table 7, and 

 daily averages of the total received on a horizontal surface are sum- 

 marized in Table 8. 



THE EFFECT OF CLOUDINESS ON THE TOTAL SOLAR RADIATION RECEIVED 



ON A HORIZONTAL SURFACE 



The relation between Qo, the radiation received with a clear sky, and 

 Qs, the amount received with an ONercast, or partly overcast sky, has been 



o 



given by Angstrom in the form of the following equation: 



Qa = QAa + (1.00 - a)S] 



where S is the percentage of possible hours of sunshine prevailing. 

 Angstrom found a to vary between 0.22 and 0.25. Our own researches 



