452 Prof. J. Trowbridge on Carbon 



t-y 



brilliancy diminishes greatly. On the other hand, an atmo- 

 sphere of oxygen greatly augments its vividness. The question 

 therefore whether oxygen exists in the sun is closely related 

 to questions in regard to the presence of carbon, when we 

 consider the temperature and light of the sun. 



If suppositions also are made in regard to the magnetic 

 condition of the atmosphere of the sun, it is of great interest 

 to determine whether oxygen exists there, for oxygen has 

 been shown by Faraday, and later by Professor Dewar, to be 

 strongly magnetic. 



Professor Henry Draper brought forward evidence to prove 

 the existence of bright oxygen lines in the solar spectrum. 

 Professor Hutchins, of Bowdoin College, and myself examined 

 this evidence, and after a long study of the oxygen spectrum 

 in comparison with the solar spectrum, came to the conclusion 

 that the bright lines of oxygen could not be distinguished in 

 the solar spectrum. We published our paper in 1885. I have 

 lately studied the subject from another standpoint ; having 

 carefully examined the regions in the solar spectrum where 

 the bright lines of oxygen should occur, if they manifest 

 themselves, in order to see if any of the fine absorption-lines of 

 iron in the spectrum of iron were absent, for it is reasonable to 

 suppose that the bright nebulous lines of oxygen would 

 obliterate the faintest lines of iron. 



The method adopted by Draper for obtaining the spectrum 

 of oxygen consisted in the employment of a powerful spark 

 in ordinary air. To obtain this spark, the current from a 

 dynamo running through the primary of a Ruhmkorf coil was 

 suitably interrupted. By the use of an alternating machine 

 and a step-up transformer, powerful sparks can be more 

 readily obtained. Since the time of exposure with a grating 

 of large dispersion is long, considerable heat is developed in 

 the transformer from tbe strong currents which are necessary 

 to produce a spark of sufficient brilliancy. I have therefore 

 modified the method in the following manner. The spark- 

 gap is enclosed in a suitable chamber, which can be exhausted. 

 When the exhaustion is pushed to a certain point, the length 

 of the spark can be increased ten or twenty times over its 

 length in air, and a suitable spark for photographic purposes 

 can therefore be obtained by the employment of far less energy 

 in the transformer. A pressure of eight to ten inches of 

 mercury in the exhausted vessel is sufficient. A quartz lens 

 inserted in the wall of the exhausted chamber serves to focus 

 the light of the spark on the slit of the spectroscope. 



The following table gives the certain oxygen lines and iron 

 lines in the same region of the spectrum : — ■ 



