52 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 6& 



H. SUBSIDIARY INVESTIGATIONS 

 (l) CORRECTION FOR SLIT AND BOLOMETER WIDTHS 



The different angular widths of the bolometer and the slit necessi- 

 tated the derivation of a new formula for reducing approximately 

 the observed spectrum intensities to what they would have been 

 with an infinitely narrow slit and bolometer. This derivation with its- 

 limitations is given in Appendix I. 



(2) FIELD ENERGY DUE TO SCATTERING 



The complication arising from the immense amount of scattered 

 light present in a spectrum of such great range of intensities (loo,- 

 000 fold) and small dispersion required extended study. This dis- 

 cussion covered the energy scattered into any region from all wave- 

 lengths as well as that scattered away. It will be found in Appendix 

 II, where a separate summary gives the generalizations. 



(3) TRANSPARENCY OF IODINE. FIGURE 12 



The need of a suitable absorbing screen to cut out the intense short 

 wave energy, the scattering from which rendered observations other- 

 wise useless in the solar spectrum, led to the preparation of a thin 

 film of iodine, 0.005 to 0.007 cm. thick between two rock salt plates 

 whose combined thickness was about i cm. The results of two 

 measures of the transparency of the iodine film are shown in 

 figure 12. 



(4) COMPARISON OF NERNST LAMP SPECTRUM WITH THAT OF BLACK BODY 



The comparison of the radiation from a black-body radiating at 

 2,200° K. (apparent black-body temperature of the lamp) to one 

 at 300° K. (the temperature of the shutter used for zero deflection) 

 is shown in figures 6, 9, and 10. The agreement, with due allowance 

 for the absorption bands, seems satisfactory down to about 10 ;u,. 

 From here on the lamp curve increasingly falls below the black-body 

 curve. It is uncertain that the lamp radiates here as a black-body 

 but the departure may be chiefly due to the decreasing- absorption 

 of the incident radiation by the soot-blacked surface of the bolometer. 



NOTE 



There are two doubtful points upon which light has been thrown 

 since the above was written: ist, May not even the small amount 

 of aqueous vapor present in the path through the spectroscope 

 exercise nearly complete and considerable absorption in narrow lines 



