500 



SCIENCE 



[N. S. Vol. XXIX. No. 743 



DISCUSSION AND 00BRE8P0NDEN0E 

 NOTE ON THE SPECTRUM OF MARS 



I THINK that Professor Very's article on 

 " The Presence of Water Vapor in the At- 

 mosphere of Mars,'" though written with the 

 kindliest feelings for all concerned, is certain 

 to convey a wrong impression as to the ob- 

 servations made by Huggins, Vogel and 

 others in the sixties and seventies and by 

 myself in 1894^5. The pioneer observers be- 

 lieved they saw in the spectrimi of Mars the 

 modifying influences of osygen and water 

 vapor in its atmosphere. I held, and pub- 

 lished, the opinion that " the polar caps on 

 Mars are conclusive evidence of an atmos- 

 phere and aqueous vapor " on that planet f 

 but my spectroscopic observations, made 

 under vastly improved conditions, convinced 

 me that oxygen and water vapor did not exist 

 in sufficient quantities to be detected by the 

 spectroscopic method as then available, for 

 this method is a very insensitive one. The 

 observations by the earlier observers, and by 

 myself, were confined to the spectral region 

 J^SiOO to ^6900. The region of wave-lengths 

 larger than '^6900 was entirely too faint for 

 visual study, and in those days we had not 

 the means of photographing it. About two 

 years ago it was discovered that the applica- 

 tion of certain chemicals to an ordinary dry- 

 plate would make it quite sensitive to radia- 

 tions of greater wave-lengths than ^6900. 

 In the region thus rendered available, at 

 ^7175, is the so-called little " a " band, due to 

 water vapor. It is this band, in a region 

 previously unobserved and unobservable in 

 Mars' spectrum, upon which Professor Very's 

 work is based exclusively. His investiga- 

 tions, therefore, afford no evidence as to the 

 correctness of the early observations. 



Now comes the point, omitted by Professor 

 Very, which does bear upon the early obser- 

 vations. The spectrum photographs used by 

 Very (made by Mr. Slipher at Flagstaff) re- 

 corded not only the new region containing 

 the band "a" but also the old region ^5400 

 to ?k6900. Mr. Slipher's published conclusion, 



' Science, January 29, 1909, p. 191. 

 'Astronomy and Astrophysics, 1894, p. "760. 



as based on his series of seven spectrum 

 photographs, is that " Aside from reinforce- 

 ment of the 'a' band (at '^7175), the spec- 

 trum of Mars shows no selective absorption 

 not found in that of the moon photographed 

 under the same conditions";' that is, the 

 effects of oxygen and water vapor on Mars 

 were no more visible in the region ^SJfOO- 

 ^6900 of the spectrum than were the effects 

 of oxygen and water vapor existing on the 

 moon! 



Only those who have seen Mr. Slipher's 

 original negatives can judge of their value; 

 but whatever their value, they are absolutely 

 confirmatory of my visual observations of 



1894, of my photographic observations of 



1895, of Professor Eeeler's photographic ob- 

 servations of 1897; and as absolutely opposed 

 to the observations of Huggins, Vogel, Maun- 

 der and others as my own observations were. 

 Readers of Very's article would get exactly 

 the opposite view. 



If Mr. Slipher, observing from a high alti- 

 tude and with little water vapor in our at- 

 mosphere to embarrass him, could see no 

 difierence between the spectra of Mars and 

 the moon in the region ^5400-'^6900, how im- 

 potent were the effects of the pioneer observ- 

 ers at sea-level, with small telescopes, looking 

 through ten times as much water vapor as 

 Mr. Slipher and I did; yet, all hail, and 

 nearly all the credit to the pioneers! Their 

 work, though unsuccessful, makes progress 

 possible by succeeding generations of investi- 

 gators. 



W. W. Campbell 



Mt. Hamilton, 

 February 6, 1909 



A NEW KIND OF PTARMIGAN 



To THE Editor of Science: The current 

 McOlure's Magazine (March, 1909) contains a 

 sonnet which I am sure will entertain the 

 readers of Science, even though it bears the 

 gruesome title " The Shipwrecked Sailor." 

 It contains this striking (in more senses than 

 one) bit of ornithological news: 



Yet he smiled, 

 Abandoning hope and drowning unaware, 

 ' Astrophysical Journal, 28, p. 403, 1908. 



