J. Trowbridge — Carbon and Oxygen in the Sun. 331 



electric furnace is due to the combustion of carbon. Can we 

 conclude that the sun is also a vast electric furnace? 



If the voltaic arc is formed under water its brilliancy dimin- 

 ishes greatly. On the other hand, an atmosphere 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 con- 

 dition 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 Hntchins 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 them- 

 selves, 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 oblit- 

 erate 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 Puhmkorf 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 

 the powerful 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 suit- 

 able 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 trans- 

 former. A pressure of eight to ten inches of mercury in the 

 exhausted vessel is sufficient. A quartz lens inserted in the 

 wells of the exhausted chamber serves to focus the light of the 

 spark on the slit of the spectroscope. 



