688 PROCEEDINGS OP THE AMERICAN ACADEMY. 



The conclusions of my work thus far are as follows : 



1. The metallic lines due to terminals in rarefied hydrogen, and 

 rarefied air, when these terminals are one centimeter apart in glass or 

 quartz capillaries, exhibit a reversed action. When this takes place it 

 is generally coincident with the position of the line when the spectrum 

 is taken in air, while the spectrum of the line on the least refrangible 

 side is much broadened. This seems to indicate a gaseous product ; an 

 oxidization or hydration due to the dissociation of the air and water 

 vapor present. 



2. Highly heated rarefied hydrogen and rarefied air passing over con- 

 taining walls of glass or amorphous silica give broad bands which ap- 

 parently coincide with narrow silicon lines of far lesser intensity. These 

 also I attribute to the dissociation of air and water vapor. The bril- 

 liancy of the light produced in this reaction is far greater when there 

 is an excess of hydrogen in the tubes than when rarefied air fills them. 

 It is a question whether lines produced by metals like silicon in their 

 difficulty of volatilization in air are really due to the metals. I am in- 

 clined to attribute some of them to the environment; that is, to a reac- 

 tion between the metal and the gases present. 



3. Spark spectra of metals appear to represent complicated reactions 

 of gases with the metallic vapor. 



4. Metallic vapor carries the main portion of an electric discharge 

 when these terminals are within three millimeters of each other in 

 rarefied hydrogen or rarefied air. The gaseous ions, if the dissociation 

 occurs, give little light. 



5. The broadening of the light accompanying the reversed lines, if 

 unsuspected, might lead one to conclude that a shift of the bright portion 

 had occurred. 



6. Since the iron lines do not appear under what seems favorable 

 conditions while aluminum lines appear; while in other cases gaseous 

 lines mask metallic spectra, it seems desirable to be cautious in regard to 

 speculations in regard to types of stars. 



7. Whatever may be the cause of the reversals of lines observed in 

 narrow capillaries of glass or of quartz, it seems to me that it is a fact 

 which should be reckoned with in photographic study of stars, especially 

 in the case of sudden changes of light. 



Jefferson Physical Laboratory, 

 Harvard University. 



vol. xxxvm. — 44 



