Trowbridge and Hutchins — Carbon in the Sun. 345 



motions only, though it seems likely that by the immense im- 

 provements in the photography of stellar spectra, the informa- 

 tion thus obtained will be far more accurate than any other. 



3. Finally there remains the determination of the velocity of 

 light by observations of the eclipses of Jupiter's satellites. If 

 the improved photometric methods practiced at the Harvard 

 observatory make it possible to observe these with sufficient 

 accuracy, the difference in the results found for the velocity of 

 light when Jupiter is nearest to and farthest from the line of 

 motion will give, not merely the motion of the solar system 

 with reference to the stars, but with reference to the lumin- 

 iferous ether itself. 



Aet. XXXVII. — On the Existence of Carbon in the Sun. Contri- 

 butions from the Physical Laboratory of Harvard University; 

 by John Trowbridge and C. C. Hutchins. 



[From the Proceedings of the American Academy of Arts and Sciences, 



vol. xxxiii.] 



From the presence of absorption bands in the solar spectrum 

 at high altitudes, Captain Abney has been led to believe in the 

 existence of certain hydrocarbons between the earth and the 

 sun ; and Siemens's theory of the conservation of solar energy 

 depends upon the supposed existence of carbon vapor in inter- 

 planetary space. It is not our purpose to discuss Abney's ob- 

 servations, or the truth of Siemens's hypothesis. We wish to 

 call attention to the remarkable character of the carbon spec- 

 trum, formed by the voltaic arc in air between carbon ter- 

 minals ; and to draw attention to the evidence presented by 

 the juxtaposed solar spectrum of the existence of carbon in 

 the sun. 



In our early experiments the carbon terminals between 

 which the voltaic arc was formed were heated several hours, 

 while a stream of chlorine gas was passed over them. This 

 operation was not entirely successful in removing metallic 

 impurities. Subsequently we discovered that the spectra of 

 these impurities could be readily distinguished from the marked 

 fluted carbon spectrum, and we therefore employed the ordinary 

 compressed carbon sticks employed in electric lighting. 



For our work the nicest adjustment of slit was necessary, in 

 order that no displacement of spectrum lines could possibly 

 occur when the carbon spectrum was photographed in juxtapo- 

 sition with the solar spectrum. This was accomplished by the 

 use of a slit, the jaws of which opened equally. 



