Rock sail in thin plates bc- 

 20 787 15 conifs opaqiu'. 8 



Langley's i-sUnial rd limil of the 

 infra-red solar spectrum. 



Lan^ley's loriKesl measured 

 waves. 10 



Flour spar in lliin i)lalcs l)e- 

 comcs opaque. 1 1 



Actual limit of LanRJcy's solar 

 spectrum, 1888-18Q0. 12 



Ordinary glass ceases to trans- 

 3 mit. ' 13 



Heat waves photographed by 

 1 2.1 lOo 111 Abney in 1886. ' 14 



1.6 Extreme red — sometimes visi- 



5 .8 ble to acute eyes. 1.^ 



VISIBLE SPECTRUM— A LITTLE LESS THAN ONE OCTAVE 



IS 



708 



16.6 



\> 



500 



20 



i: s 







1 1 



433 



27 



0.4 







5.,^ 



208 



57 



3.2 











Millions of 







Reference: 



Anstrom 



Millionths Millions per 



Limit of perception 



of 



red to 





Units 



of In. 



Second 



average eye. 







16 



7600 







Red. 









6700 





389 



Orange. 









6500 



26 



461 



Yellow. 









5830 



2?, 2 



515 



Green. 







17 



5510 



22 



544 



Peacock. 









5120 



20.5 



586 



Blue. 









4750 



10 



632 



Violet. 









44Q0 



18 



666 



Limit of perception 



of 



violet 





4004 



16 



750 



to the average eye. 









3000 







Extreme limit of v 



isibility in 





3600 







acute vision. 







18 



ULTRA VIOLET SPECTRUM— TWO OCTAVES 



Wave Length Frequency References 



Millions of Note : The disruptive spark 



Anstrom Millionths Milhons per spectra of iron and cobalt 



Octav-es L^nits of In. Second shows 80% of radiation with- 



3600 14.4 820 in the limits of the bracket 



3380 13.3 888 ("Pfluger") Am de Phys (4) 



3000 11.8 1000 13— P 890— (1904) 



1 2800) Ultra violet begins (approxim- 



) ately) 



2790) 11. 1075 Flint glass ceases to transmit 19 



2480) 9.76 1210 Stoke's limit of the solar spec- 



2150) 8.46 1418 trum. 20 



) Note: In Manila the limit was 



2020) 7.95 1485 found to be 2190 A. U. 



2002 ) Light crown glass ceases to 



1850) 7.28 1622 transmit. 21 



1800) Ordinary clear quartz begins to 



1700 6.69 1765 absorb. 



2 1500 Clear calcite in thin plates be- 

 1350 gins to absorb. 23 

 1230 Miller's photographic limit. 24 

 1000 3.937 3000 Stoke's hmit of fluorescence. 25 



Limit of transparency of finest 

 quartz in very thin plates. 26 



27 



36 



