110 Nichols and Franklin — A Spectro-photometric 



Table IV. 



Daylight by clear and by clouded sky, compared with the 

 incandescent lamp. 



light of a 16-candle 



Sky Cloudless. 



Measurements of 

 H. C. Vogel 

 (.Reduced). 



Wave- 

 lengths, 



6330 

 6000 

 5890 

 5550 

 5170 

 4860 

 4640 



4440 

 4260 



Daylight 

 Petroleum. 



0-50 

 0-79 

 1-00 

 2-00 

 5-00 

 10-52 

 22-22 



50-00 

 100-00 



Measurements of 

 Nichols and 

 franklin. 



Wave- 

 lengths. 



6685 

 6080 

 5890 

 5570 

 5185 

 4920 

 4685 

 4500 



Daylight 

 Standard. 



0-32 

 0-75 

 1-00 

 1-69 

 4-19 

 733 

 16-79 

 21-37 



Sky Overcast. 



Measurements of 

 H. C. Vogel. 

 (Reduced). 



Wave- 



Daylight 



lengths. 



Petroleum. 











6330 



0-52 



600 



0-84 



5890 



1-00 



5550 



1-78 



5170 



3-80 



4860 



7-77 



4640 



13-74 



4440 



17-80 



4260 



19-84 



Measurements of 



Nichols and 



Franklin. 



Wave- 

 lengths. 



7530 

 6685 

 6080 

 5890 

 5570 

 5185 

 4920 

 4685 

 4500 



Daylight 

 Standard. 



0-13 

 0-45 

 0-90 

 1-00 

 1-50 

 2-79 

 4-59 

 6-45 

 9 08 



Table V. 



Sunlight, compared with a petroleum flame (reduced from the measurements of 



H. C. Vogel). 





Sunlight. 



Wave-lengths. 



Petroleum flame. 



6330 



0-57 



6000 



0-75 



5890 



1-00 



5550 



1-31 



5170 



2-53 



4860 



4-87 



4640 



7-30 



4440 



11-93 



4260 



13-16 



The only American observer, Mr. "W. H. Pickering, has, how- 

 ever, obtained values for the relative brightness of the sun's 

 rays which agree very closely indeed with those for day -light 

 by nnclouded sky, as observed by Yogel and by ourselves. 

 Thus Pickering finds for the violet 

 Sunlight 



A=4550 



:23-Y7 (reduced). 



Gaslight" 

 Our value for the same region (see table IV), is, 



A = 4500: 



Daylight „, ow 

 J e — =21-37 



Standard 



Yogel's result, in nearly the same portion of the spectrum is, 



Daylight . , 



=: * s „ =22-22 (reduced). 



.Petroleum name ' 



A=4640 



