3.1.0 Prof. Trowbridge and Mr. Hutchins on 



In regard to the other three spectra of oxygen of Schuster 

 we have nothing to say ; but so far as concerns the spark 

 spectrum in air and the solar spectrum from wave-lengths 

 3749*8 to 5033*85 we can safely affirm that there is no 

 physical connexion between them. 



XL. On the Existence of Carbon in the Sun. 

 By Professor John Trowbridge and 0. C. Hutchins"*. 



EROM 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 vapour 

 in interplanetary space. It is not our purpose to discuss 

 Abney's observations, or the truth of Siemens's hypothesis. 

 We wish to call attention to the remarkable character of the 

 carbon spectrum, formed by the Voltaic arc in air between 

 carbon terminals ; 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 juxta- 

 position with the solar spectrum. This was accomplished by 

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



One of Rowland's concave gratings, of 21 feet 6 inches in 

 curvature and 14,000 lines to the inch, was employed. In 

 order to avoid any possible displacement of the photographic 

 camera during the operation of photographing the carbon 

 spectrum immediately below the solar spectrum, a drop- 

 shutter was arranged directly in front of the sensitive plate, 

 the movement of which was independent of any movement 



* From an advance proof from the Proceedings of the American 

 Academy of Arts and Sciences, vol. xxiii. Communicated by Professor 

 J. Trowbridge, of Harvard University, Cambridge, Mass., U.S. 



