20 PLEASANT WAYS IN SCIENCE. 



attempt at this time," he proceeds, " to give a complete list 

 of the oxygen lines, . . . and it will be noticed that some 

 lines in the air spectrum which have bright anologues in the 

 sun are not marked with the symbol of oxygen. This is 

 because there has not yet been an opportunity to make the 

 necessary detailed comparisons. In order to be certain that 

 a line belongs to oxygen, I have compared, under various 

 pressures, the spectra of air, oxygen, nitrogen, carbonic acid, 

 carburetted hydrogen, hydrogen, and cyanogen. 



"As to the spectrum of nitrogen and the existence of 

 this element in the sun there is not yet certainty. Never- 

 theless, even by comparing the diffused nitrogen lines of this 

 particular photograph, in which nitrogen has been sacrificed 

 to get the best effect for oxygen, the character of the evidence 

 appears. There is a triple band somewhat diffused in the 

 photograph belonging to nitrogen, which has its appropriate 

 representative in the solar spectrum, and another band of 

 nitrogen is similarly represented." Dr. Draper states that 

 " in another photograph a heavy nitrogen line which in the 

 present one lies opposite an insufficiently exposed part of 

 the solar spectrum, corresponds to a comparison band in the 

 sun." 



But one of the most remarkable points in Dr. Draper's 

 paper is what he tells us respecting the visibility of these 

 lines in the spectrum itself. They fall, as I have mentioned, 

 in a part of the spectrum where the actinic energy is great 

 but the luminosity small; in fact, while this part of the 

 spectrum is the very strongest for photography, it is close to 

 the region of the visible spectrum, 



" Where the last gleamings of refracted light 

 Die in the fainting violet away. " 



It is therefore to be expected that those, if any, of the bright 

 lines of oxygen, will be least favourably shown for direct 

 vision, and most favourably for what might almost be called 

 photographic vision, where we see what photography records 

 for us. Yet Dr. Draper states that these bright lines of 



