Trowbridge and Hutchins—Carbon in the Sun. 345
motions only, though .it seems likely that by the immense improvements in the photography of stellar spectra, the information 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.
Art. XXXVII.—On the Existence of Carbon in the Sun. Contributions 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 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 juxtaposition with the solar spectrum. This was accomplished by the use of a slit, the jaws of which opened equally.
