12 



Prof. S. P. Langley on Energy and Vision. 



2nd series : observer, F. W. Y. ; time, 1*^ 15°» to 2" 30"^ 

 P.M. ; air-mass, 1*28 atmospheres. 



April 4tli. — " A good blue at first, after 12'' milky blue 

 from slight smoke, but still a fairly good sky." 



1st series : observer, F. W. V. ; time, lO'^ 25°* to IP 55°» 

 A.M. ; air mass, 1*23 atmospheres. 



2nd series : observer, E. M. ; time, 12*^ 30"^ to P 30°* P.M.; 

 air-mass, 1*20 atmospheres. 



April 6th. — Sky " good blue, quite clear ; " observer, 

 F. W. V. ; time, 10*' 45°i a.m. to 12'^ 15"^ p.m. ; air-mass, 1-18 

 atmospheres. 



June 16th. — Sky " clear, good blue ; after 1 p.m. cirrus 

 streaks ;" observer, B. E. L. ; time, ll'' IS"" A.M. to I'' 45°^ 

 p.m. ; air-mass, 1*05 atmospheres. 



July 2nd. — Sky " clear, excellent 5 " observer, B. E . L. 



1st series : time, ll*" 25^^ A.M. to 12^" 15°^ p.m. ; air-mass, 

 1'03 atmospheres. 



2nd series : time, 12'' 15™ p.m. to 1^ 25°^ p.m. ; air-mass, 

 1*02 atmospheres. 



We first give in Table IV. the values of the photometric 

 measurements in the prismatic spectrum, reduced to the 

 standard conditions above cited. 



Table IV. — Showing sensitiveness of the eye to light, as 

 deduced from the power to decipher fine print. Prismatic 

 (uncorrected)values : — 



\= 



0'^-35 



0''-38 



0'^-40 



0'^-45 



Of'-SO 



Of'-SS 



of^-eo 



0'^'65 



0^^-70 



0^-1b 



1 



S. p. L. 

























Mar. 30. 









0-29 



3-01 



19-31 



19-15 



3-88 



0-28 







F.W.V. 

























April 2. 







013 



9-89 



57-94 



1133 



15-14 



1-06 



0-27 







April 3. 







0-30 



9-88 



1.54-2 



167-9 



26-91 



1-99 



0-43 







April 4. 







0-20 



10-88 



154-6 



193-8 



24-62 



2-23 



0-33 







April 6. 



0-0015* 



0017* 



0-17* 











2-32 





0005* 



000 



Mean ... 



0-0015 



0-017 



0-20 



10-22 



122-25 



158-33 



22-22 



1-90 



0-34 



0-005 



0-00 



B. E. L. 























June 16. 







0-24 



30-60 



157-2 



2170 



36-98 



3-39 



017 



0-001* 





July 2. 



0-000* 



0003* 



0-23 



10-89 



125-7 



142-3 



33-96 



4-54 



0-73 



0-004* 





July 2. 







0-34 



35-38 



186-1 



158-7 



70-16 



5-98 



0-75 







Mean ... 



0-000 



0003 



0-27 



25-62 



166-3 



172-7 



47-03 



4-64 



0-55 



0-002 





E. M. 

























April 3. 







0-35 



30-60 



100-1 



146-1 



49-82 



5-85 



1-46 







April 4. 







0-19 



8-34 



46-39 



75-27 



4205 



3-04 









Mean ... 







0-27 



19-47 



73-25 



11069 



45 94 



4-45 



1-46 







* Blue (cobalt) glass over slit Sj. 



