270 Trowbridge and Hutchins — Oxygen in the Sun. 



reproduced in the corresponding lines in the solar spectrum. 

 The test of coincidence, therefore, requires primarily a normal 

 spectrum and the highest possible dispersion. The earlier 

 observers were limited to the instruments of small dispersion, 

 and the entire number of lines observed in the solar spectrum 

 was small compared with that given by the best modern ap- 

 paratus. The chances for an apparent coincidence were there- 

 fore much greater, and evidence of a very misleading character 

 could be obtained. 



In Dr. H. Draper's published photograph, the coincidence of 

 the greater part of the oxygen lines with bright bands in the 

 solar spectrum is striking; and it is not a matter of sur- 

 prise that he was led to conclude the connection between the 

 two spectra to be a physical one, and to announce the existence 

 of oxygen in the sun as proved. Instances are not infrequent 

 where instrumental imperfection or lack of power has led to 

 results unsupported by later and more powerful research. 

 "Witness the spots of Venus of the older observers. Now when 

 we apply to the spectra of the sun and oxygen a dispersion and 

 definition that show the minute detail of each, the '* bright 

 bands " at once vanish, or no longer appear as such, and all 

 the apparent connections between them and the oxygen lines 

 disappears also. The bright bands of Dr. H. Draper's spectrum 

 are found to be occupied by numerous dark lines, of various 

 degrees of intensity ; but the hypothesis of Prof. J. C. Draper, 

 that these are the true representatives of the oxj^gen lines, is 

 rendered untenable by the lack of any systematic connection 

 between the two. It happens quite frequently that an oxygen 

 line falls centrally upon the space between two dark lines of the 

 solar spectrum, but not more frequently than we might expect 

 as a matter of chance, when we consider the vast number of 

 lines and spaces ; and the fact that the spaces are no brighter 

 than the surrounding background of the solar spectrum would 

 not seem to permit of their interpretation as bright lines. 



The subject of bright lines in the solar spectrum is one upon 

 which men will probably differ, and we have sought informa- 

 tion upon it. Of course there is no a priori reason why such 

 bright lines should not exist, as they do in many stars; but we 

 have photographed the sun's spectrum every day that the sun 

 has shone for nearly five months, without finding a line that could 

 with certainty be pronounced brighter than its neighbors ; and 

 it must be admitted that the photograph is the best of photo- 

 meters in such a case. 



In regard to the other three spectra of oxygen of Schuster 

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

 trum in air and the solar spectrum from wave-lengths 3749*8 

 to 5033*85 we can safely affirm that there is no physical con- 

 nection between them. 



