10 PROCEEDINGS OF THE AMERICAN ACADEMY 



Investigations on Light and Heat, made and published wholly or in part with 

 Appropriation from the Rumford .Fund. 



II. 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF 

 HARVARD UNIVERSITY. 



ON THE EXISTENCE OF CARBON IN THE SUN. 



By John Trowbridge and C. C. Hutchins. 



Presented March 9, 1887. 



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 Sieraens's 

 theory of the conservation of solar energy depends upon the sup- 

 posed existence of carbon vapor 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 car- 

 bon 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 discov- 

 ered 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 juxtaposition 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 



