ON THE ABSORPTION AND EMISSION OF 

 AIR AND ITS INGREDIENTS FOR LIGHT 

 OF WAVE-LENGTHS FROM 250.. TO 100 



/i/A. 



By Victok Schumann, Pii.l). 



(Translated from the German Manuscrh't by Chakles S. Peirce.) 



The present report describes the most essential I'esults obtained up to the end 

 of the year 1900 in an unfinished investigation which was begun at the end of 

 March of the same yeai', and was continued without interruption during the in- 

 terval, this research having had the support of a grant from the Hodgkins Fund of 

 the Smithsonian Institution. 



General co/mderatio/id. — The chief instrument of this investigation was a 

 vacuum-spectrogi'aph with lenses and piism of white fluor-spar. 



In a general way, its mechanical arrangement is that of an ordinary spec- 

 troscope with collimator and telescope ; except that a little photographic camera 

 takes the place of the eye-piece. Its parts, however, have air-tight connections, 

 so that a high vacuum can be produced in it by a mercurial air-pump. 



Figs. 1 to 9 ai'e photographic reproductions of the original woi-king drawings 

 in accordance with which the apparatus was constructed by my own hands; so 

 that any instrument-maker who may desire to undertake the execution of such a 

 vacuum-spectrograph may trust implicitly to these figui'es. The following ex- 

 planations may be useful. 



Fifs. 1 and 2 show the photographic plate-holder open. It is adapted to 



plates 37 x 12.7 mm. 



Y'v. 3 shows a key by means of which the plate-holder can be shoved into the 

 camera, and by which it can also be withdrawn. 



Fig. 4 is the slit with its three micrometers, a", t", y". The first of these, a" 

 (1 division = 0.001 mm.), regulates the width of the slit. The second, f (1 

 division = 0.01 mm.), adjusts the length of the slit. The third, y" (1 division = 

 0.1 mm.), serves to shift the adjustable diaphragm which regulates the length to 

 any part 'of the slit that it may be desired to employ. The sci-ew c" effects the 



