66 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 



under observation. The total field light therefore ranges (last 

 column) from 20 to 30 per cent greater than that observed with the 

 quartz plate. This added amount depends on the shape of the energy 

 curve. It is somewhat less the greater the amount of water vapor 

 because of the considerable absorption by the water vapor of the 

 energy less than 9 ^ which plays such a disturbing role in the pro- 

 duction of field energy. 



SUMMARY 



The following table gives a summary indicating the amounts and 

 increasing importance of the scattered light with increasing angular 

 deviation. This increasing importance with increasing prismatic 

 deviation depends on the more rapid decrease of the energy in the 

 prismatic spectrum than in the scattered band of energy overlapping 

 this spectrum. 



Table 17.- — Fjeld Licht Summary 



1 Wave-length in (,u) 1.8 



2 Deviation in (') o 



3 Deviation in (cm.) o 



4 Quartz transmits 85,000 



5 1 . 18 X ditto 100,000 



6 Total field light 



7 Black-body radiation' 100,000 |8,ooo 



8 Nernst lamp 100,0008,000 



Line i gives the wave-lengths in millionths of a meter (n). 



Line 2 gives the difference of deviation in minutes of arc (') in a 15° rock- 

 salt prismatic spectrum, the deviation at 1.8 |x being taken as zero. 



Line 3 gives these differences as cm. measured on the plate i cm. = 4'. 



Line 4 gives the Nernst-lamp spectrum observed through a quartz plate, 

 h cm. thick. The energy indicated belongs to the deviation but not to the 

 wave-lengths indicated as it must be all of wave-lengths transmissible by 

 quartz, namely, less than 4 |x. 



Line 5 is 1.18 times line 4, allowing for reflection of energy of wave-length 

 less than 4 yi from the quartz surfaces. It nearly represents the energy- 

 curve of a monochromatic line of intensitj' 100,000 together with the energy 

 scattered to the long wave-length side. See curve abiCi of figure 18 for a 

 representation of this energy curve. 



Line 6 is line 5 increased liy the process developed in this appendix to give 

 the total light scattered from all wave-lengths as it would occur in the spec- 

 trum of a Nernst lamp when the intensity of the latter is taken as 100,000 

 at 1.8 M- (see line 8). These values are represented by the curves b2C2' of 

 figure 18. 



Line 7 computed relative intensities in the black-body spectrum of a source 

 at 2,200° K. radiating to a similar one at 300° K., corrected for absorptions. 



