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XLYIII. Carbon and Oxygen in the Sun, 

 By John Trowbridge*. 



IN 1887 Professor Hutchins, of Bowdoin College, and 

 myself brought forward evidence to show that the peculiar 

 bands of the voltaic-arc spectrum of carbon can be detected in 

 the sun's spectrum. They are, however, almost obliterated by 

 the overlying absorption-lines of other metals, especially by the 

 lines due to iron. In order to form an idea of the amount of 

 iron in the atmosphere of the sun which would be necessary 

 to obliterate the banded spectra of carbon, I have compared 

 the spectrum of carbon with that of carbon dust, and a defi- 

 nite proportion of iron distributed uniformly through it. The 

 carbon dust and iron reduced by hydrogen was formed into 

 pencils suitable for forming the arcf. Chemical analysis 

 showed that the iron was uniformly mixed with the carbon 

 dust ; specimens taken from different sections of the terminals 

 showed in the carbons which I burned in the electric arc 

 28 per cent, of iron and 72 per cent, of carbon. 



The method of experimenting was as follows : — That por- 

 tion of the spectrum of the sun which contains traces of the 

 peculiar carbon band lying at wave-length 3883*7, and which 

 had been almost obliterated by the lines of absorption of other 

 metals, among them those of iron, was photographed. The 

 pure carbon banded spectrum was photographed on the same 

 plate immediately below the solar spectrum, and the spectrum 

 of the mixture of iron and carbon immediately below this. 

 The sun's spectrum can be regarded as a composite photo- 

 graph, and the iron and carbon can also be regarded as a 

 composite photograph. It was speedily seen that from 28 to 

 30 per cent, of iron in combination with 72 to 70 per cent, of 

 carbon almost completely obliterated the peculiar banded 

 spectrum of carbon. This proportion, therefore, of iron in 

 the atmosphere of the sun, were there no vapours of other 

 metals present, would be sufficient to prevent our seeing the 

 full spectrum of carbon. 



The iron in the carbon terminals which I employed greatly 

 increased the conductivity, as will be seen from Table I., 

 which was obtained in the following manner. 



The carbons were separated by means of a micrometer- 

 screw, and the current and difference of potential were mea- 



* Communicated by the Author. 



t I am indebted to Mr. John Lee, of the American Bell Telephone Co., 

 for his skill in making the carbons and for analysis of the composite 

 carbons. 



