440 



NATURE 



[June 9, 1910 



vol. cxlix., No. 17, p. 666) by two charts (Fig. i), on one 

 of which M. Fournier had recorded the features seen 

 during June, July, and part of August, whilst the other 

 showed the increased contrast of the same features later in 

 August and during September. 



It was not until the beginning of the latter month that 

 the accustomed contrasts and details completely reasserted 

 themselves and permitted the work of confirmation and 

 discovery to proceed normally. 



M. Antoniadi suggests that this masking effect was 



MARS DURING THE RECENT OPPOSITION. 



CO far as can be judged from those yet published, the 

 •^ results accruing from the observations of Mars made 

 during the opposition of 1909 are, in a sense, disappoint- 

 ing. The favourable conditions of the opposition, as 

 regards the altitude and the apparent diameter of the 

 planet, engendered the hope, in many minds, that most 

 of the outstanding problems in the Martian enigma would 

 be solved more or less definitely. Yet the camps into 

 which areo- 

 graphers are 

 divided are still 

 at issue, and 

 the differences 

 appear to be at 

 least as sharply 

 accentuated as 

 before. To the 

 one side the 

 canali are still 

 continuous chan- 

 nels, set out 

 with a rectitude 

 more or less 

 geometrical, and 

 having " oases " 

 around the reser- 

 voirs upon 

 which they 

 appear to con- 

 verge ; but to 

 the opposition 

 these clearly cut 

 channels are but 

 alignments of 

 dark spots 

 merged into 

 apparent con- 

 tinuity by a 

 p h y s i o 1 ogical 

 illusion. 



However, 

 many of the 

 larger features 

 are beyond dis- 

 pute, and many 

 valuable obser- 

 vations of their 

 appearances and 

 changes have 

 been made since 

 July last. One 

 very remarkable 

 phenomenon was 

 noted, and has 

 been discussed 

 by practically 

 every observer, 

 viz. the appar- 

 ent veiling of 

 the planet's sur- 

 face during the 

 earlier part of 

 the opposition. 



In June, Jul}', 

 and August the 

 details, and even 

 some of the 

 larger features, 

 were not dis- 

 cernible ; there 

 was a general 



lack of contrast between the light and the dark I caused by the interposition of light, cirrus cloud in 

 areas. Thus M. Antoniadi, using the 24-cm. refractor at planet's atmosphere, such cloud being filmy in structi 

 Juvisy, reported {Bull, de la Soc. astron. de France, ! and yellowish in colour, so that it reduced the usual c^ 

 September, 1909, p. 386) that, on August 11 and 12, the trasts without totally obscuring the features. This is 

 surface of Mars was hardly recognisable, and it was with accordance with Prof. W. H. Pickering's observations 

 great difficulty that he assured himself that it was the 1895, when he found that his photographs suggested so: 

 region of the Mer de Sablier on which he was looking. 

 M. Jarry Desloges also emphasised the unusual appear- 

 ance of the planet, which he illustrated (Comptes rendus, 



NO. 2 1 19, VOL. 83] 



Fig. I.— Comparison of the appearance of the surface of Mars on diflferent dates in 1909. 



such yellow screen. 



The importance of the acknowledged existence of clout 

 must not be lost sight of in the discussion as to the aqueoi 



