Intelligence and Miscellaneous Articles. 7o 



and probably by the atmosphere which surrounds it. The other lines 

 in the red may be identical, at least in part, with B and a and the 

 adjacent lines of the solar spectrum. 



On February 14, faint lines were seen on both sides of Fraun- 

 hofer's D. The lines on the more refrangible side of D were stronger 

 than the less refrangible lines. These lines occupy positions in the 

 spectrum apparently coincident with groups of lines which make 

 their appearance when the sun's light traverses the lower strata of 

 the atmosphere, and which are therefore supposed to be produced 

 by the absorption of gases or vapours existing in our atmosphere. 

 The lines in the spectrum of Mars probably indicate the existence 

 of similar matter in the planet's atmosphere. I suspected that these 

 lines were most distinct in the light from the margin of the planet's 

 disk ; but this observation was to some extent uncertain. That these 

 lines were not produced by the portion of the earth's atmosphere 

 through which the light of Mars had passed, was shown hy the ab- 

 sence of similar lines in the spectrum of the moon, which at the 

 time of observation had a smaller altitude than Mars. 



I observed also the spectra of the darker portions of the planet's 

 disk. The spectrum of the dark zone beneath the Southern Polar 

 spot appeared as a dusky band when compared with the spectra of 

 the adjoining brighter parts of the planet. This fainter spectrum 

 appeared to possess a uniform depth of shade throughout its length. 

 This observation would indicate that the material which forms the 

 darker parts of the planet's surface absorbs all the rays of the spec- 

 trum equally. These portions, therefore, should be neutral, or nearly 

 so, in colour. 



I do not now regard the ruddy colour of Mars as due to an 

 elective absorption — that is, an absorption of certain rays only, so 

 as to produce dark lines in the spectrum. 



Further, it does not appear to be probable that the ruddy tint 

 which distinguishes Mars has its origin in the planet's atmosphere ; 

 for the light reflected from the polar regions is free from colour, 

 though this light has traversed a longer column of atmosphere than 

 the light from the central parts of the disk. It is in the central 

 parts of the disk that the colour is most marked. If indeed the 

 colour be produced by the planet's atmosphere, it must be referred 

 to peculiar conditions of it which exist only in connexion with par- 

 ticular portions of the planetary surface. The evidence we possess 

 at present appears to support the opinion that the planet's distinc- 

 tive colour has its origin in the material of which some parts of its 

 surface are composed. Mr. Lockyer's observation that the colour is 

 most intense when the planet's atmosphere is free from clouds, ob- 

 viously admits of an interpretation in accordance with this view. 



This opinion appears to receive support from the photometric ob- 

 servations of Seidel and Zollner, some of the results of which I will 

 briefly state. 



These observations show that Mars resembles the moon in the 

 anomalous amount of variation of the light reflected from it as it 

 increases and decreases in phase — also in the greater brilliancy of 



