August 5, 1910] 



SCIENCE 



177" 



verge of the barely visible. For instance, 

 examining a particular line to which Rowland 

 assigns the intensity and character denoted in 

 his notation by the symbols 0000 N d ? (mean- 

 ing one of the faintest lines, hazy and sus- 

 pected of duplicity) on the excellent photo- 

 graph by Higgs, I find this line to be invisible 

 throughout a large part of its extent; but at a 

 particular spot on the spectrogram the line 

 conies out clearly double, then disappears, and 

 is only seen again as a faint nebulous spot at 

 another point in the line. Here the variations 

 of sensitiveness at different points on the 

 same photographic plate are responsible for 

 changes from the clear definition of a close 

 double, to invisibility. How absurd would be 

 the proposition that this particular line must 

 he dropped from the list of acquired data of 

 solar spectroscopy, because it may fail to ap- 

 pear on a given plate ! A fact of science 

 which is diificult to determine, being once 

 acquired, is not overturned because of failure 

 to reproduce it. If the previous determina- 

 tion is satisfactory, the only assignable weight 

 which can be given to the failure is zero. 



It is quite possible that the renewed failure 

 of Campbell and Albreeht to secure positive 

 evidence of either water-vapor or oxygen in 

 the Martian spectrum'' is to be attributed to 

 photographic difficulties; but the influence of 

 the high dilution, that is to say, of the greater 

 altitude and lower pressure of the Martian 

 atmosphere, should not be overlooked. 



We know from the behavior of different 

 emission lines in the spectrum of the same 

 element under varying conditions of tempera- 

 ture, pressure or mode of electrical excitation, 

 that individual lines, even when very strong, 

 may disappear at the same time that weaker 

 lines are reenforced. These and other varia- 

 tions are to be expected in the lines of absorp- 

 tion also. Before the significance of the ab- 

 sence of particular spectral lines can be de- 

 termined, a critical study of the causes of 

 their variation needs to be made; and if, in 

 addition, the lines are very weak and barely 

 capable of being photographed, the uncertain- 

 ties of the photographic process must also be 

 considered. 



'Science, June 24, 1910, p. 990. 



In Lich Olservatory Bulletin, No. 169, Pro- 

 fessor Campbell subscribes to the opinion, 

 held by Vogel and Keeler, "that high re- 

 solving power was not necessary, or even 

 desirable, in visual observations of spectra no 

 brighter than those of Mars and the moon." 

 This of course does not necessarily apply to 

 photographic spectra; but we may inquire 

 whether, owing to a broadening and weaken- 

 ing of individual absorption lines when a 

 given mass of absorbent is distributed through 

 a large volume of diluent, the effect of a 

 group of broad and faint lines, combined into 

 one indistinguishable band in an instrument 

 of low power, may not be more easily recog- 

 nized than individual lines photographed with 

 high dispersion; and whether possibly the pe- 

 culiar conditions of the Martian atmosphere 

 may not favor such a constitution of the 

 Martian, as distinguished from the terrestrial 

 bands ? 



Frank W. Very 



Westwood Asteophtsical Observatoky, 

 Westwood, Mass., 

 June 28, 1910 



Addendum: The method of distinguishing- 

 Martian and telluric absorption lines by the 

 velocity-shift of the Martian lines at quadra- 

 ture is not new. It was not only explained 

 and advocated by Dr. Percival Lowell, but 

 was actually tested at the Lowell Observatory 

 by Dr. Slipher in 1905, with the same negative ■ 

 result that Professor Campbell and Dr. 

 Albreeht now obtain in repeating the experi- 

 ment. A full account of the method and its 

 results was published at the time in Lowell 

 Observatory Bulletin, No. 17. That the 

 method is not a delicate one is shown by its 

 failure hitherto, when applied to Venus which 

 possesses an undoubted atmosphere. 



F. W. V. 



QUOTATIONS 



MEDICAL APPOINTMENTS AT VIENNA 



The half-hearted way in which the requests 

 of Professor Striimpell for a modern outfit for 

 his clinic were met by the authorities has had 

 an unexpected result. The professor has 

 "given notice" he will leave his post at once- 



