November S. 1894] 



JV.-l TURE 



41 



been observed at FlagstaHf every night, with buc fe»v exceptions, 

 since the beginning of June. British astronomers would like to 

 be blessed with similar favourable opportunities. 



A noteworthy feature of Mr. Lowell's previous paper was 

 the large area occupied by the dark regions on Mars, while 

 those singular, tilted peninsulas that are so generally repre- 

 sented connecting the continents wiih the island, to the south 

 were conspicuous by their absence. At that time one continuous 

 belt of bluish-green stretched unbroken from the Hour-glass 

 Sea to the columns of Hercules, or rather to where this pass 

 should have been, for it wasnat visible. Now (September lo) 

 the continuity is cut. Hesperia has reappeared, and it has done 

 this in just the way we should expect it to show were it land 

 drying off by a sinking of the general water level. Simul- 

 taneously, the region formerly occupied by the polar sea and 

 the region to the north of it from having been blue, has now 

 become for the most part reddish yellow. This reappearance 

 of Hesperia and change of colour of the regions farther south 

 is not due to increasing distinctness of vision consequent upon 

 the nearer approach of the two planets. Had Hesperia been 

 then of anything like the brightness it is now it could not have 

 been invisible. Furthermore, Eridania is at present one of the 

 brightest parts of the disc, not only as it comes round into view, 

 but in mid-career acro-s. East, and mt least in significance, 

 the polar sea has shrunk to a thin line in keeping with the 

 diminished size of the polar cap itself. All this water has gone 

 somewhere. 



What may be the condition of these seemingly amphibious 

 lands, whether they be marsh chiefly water at one time and 

 dry land at another ; or whether their dark colour be due lo 

 vegetation which sprouted under the action of the water, and 

 then died when it withdrew, is a moot point. Mr. Lowell's 

 opinion is that it is half and half; that the transference of 

 the water is chiefly a surface one, and that the layer of water 

 is almost everywhere so shallow as to be soon drained off. His 

 reasons for believing the aqueous circulation to be a surface one 

 are many. In the first place, with the exception of certain 

 peculiar appearances near the south pole, there is no evidence 

 of anything like clouds or mist observable upon the planet, 

 nor has there been since the oljservations began. On the con- 

 trary, all parts of the surface seem to be revealed unveiled. 

 For an aerial circulation the only supposition at all feasible 

 is thought to be that of a heavy, nigh'ly dew, advanced by Prof. 

 Pickering. There ari strong reasons in the probable constitu- 

 tion of the Martian atmosphere for believing this possible. But 

 in view of certain facts connected with the canals, and referred 

 to later, the dew theory seems to be improbable. 



As to how much of the dark areas are water, and how much 

 vegetation, there is as yet no evidence to decide. Prof. Picker- 

 ing has made some ingenious polariscopic observations to this 

 end, but the difliculties inherent in the process are such as to 

 preclude definite answer as yet. At first the polar sea seemed 

 to show evidence of polarisation, confirming what we knew 

 before of its watery character. Later the lakes, polar sea, and 

 dark areas alike revealed no trace of it. Inasmuch, then, as 

 there is every reason to suspect the polar sea, at least, to be 

 water, we are left in doubt as to the adequacy of the instru- 

 mental means to detect at present such minute phenomena. 



Since Mr. Lowell's last paper, irregularities have been de- 

 tected at Flagstaff in the Martian terminator. These fall for 

 the most part under two heads, of which one is practically new. 

 It consists of certain polygonal flattenings first observed on Tune 

 30 by .Mr. Douglass. Since then these irregularities have become 

 so conspicuous that it is now difficult not to see one of them 

 in the course of an hour's observation. Sometimes they show 

 as simple slices shaved oft" the terminator, a paring of the 

 plaiiet s surface ; sometimes they appear bordered by enclosing 

 projections. They range from twenty to forty degrees wide. 

 But the suggestive thing about them is that they show almost 

 iQvariably upon that part of the terminator where the darker of 

 the dark regions is then passing out of sight. 



At first sight it might seem as if the observed appearance 

 were directly due to the darker areas lying at a lower levsl than 

 the rest of the surface. But the connection is not so simply 

 direct. For Mr. Lowell points out that were it due to a zone 

 of low-level lying between zones of higher al'itude, it could be 

 observed only as a limb effect in this case still farther diminished 

 by the cosine of the phase angle, a quantity far too saiall to 

 be observable. 



Nor will variations in slope explain the phenomemn. For 



NO. 1306, VOL. 51] 



to have an area show as a depression on account of its slope, 

 either the areas on both sides of it must be rising in altitude, 

 or the area itself must be falling in height, and this state of 

 affairs could not go on for ever unless the surface were an im- 

 possible spiral. So that the persistency of this flattening is 

 thus unaccounted for. 



Prof. Story has suggested that these dark areas have 

 smooth surfaces such as water would have. In this case, 

 remarks Mr. Lowell, the reflection from them, by which 

 alone they would be perceptible, would diminish much 

 more rapidly from the centre to the side than would be 

 the case with regions having rough surfaces, such as deserts. 

 It may be added that though a rough surface, properly 

 constructed, might obliterate itself by its own shadows, this 

 could not happen to either a desert or a forest or a grass-grown 

 plain. 



The second kind of irregularities are projections, or small 

 notches, such as are visible upon the lunar terminator ; only 

 that the Martian ones are much less pronounced. They are 

 probably due to mountains which seem to be of no great 

 height. The first of these was observed by Mr. Douglass on 

 June 30. An especially prominent one he noted on .\ugust 19. 

 It consisted of a projection flanked by a long shadow'cutling 

 into the planet obliquely. He measured the shadow's length 

 at 35". Taking the obliquity into account, this seems to imply 

 a range the length of whose projection would be about 2". It 

 is difficult to say how much of this is due to irradiation ; 

 especially as each observer differs. The best tests Mr. Lowell 

 has been able to make give a probable average of about five- 

 sevenths of a tenth of a second of arc with the power then 

 applied, about 640. Calling the terminal projection of this 

 range therefore 'is", its height appears to be about 3700 feet. 

 But the smallness of the quantity measured and the uncertainty 

 of the factor of irradiation renders the result largely indefinite. 



A consequence of the slope on the effect of these mountains 

 is interesting. For an elevation need not appear as such. 

 What would show as a projection on the nether side of the 

 terminator would appear as a depression on the hither one. 



Interesting plateaus were observed on two occasions by Prof. 

 Pickering. One of these lies in Phastontis not far from the 

 columns of Hercules, which thus seem to have been most 

 appositely named. Both plateaus rise abruptly, are surprisingly 

 level on top, and stand at about the same height, a height 

 which from the reduced measurements does not probably exceed 

 2600 feet. 



On Mars the second kind of irregularity is less common than 

 the first, and the elevations indicated are apparently never 

 what we should call high. We may therefore conclude that 

 the Martian surface is, as compared with our terrestrial one, 

 rel.atively flat. 



Certain avhitish pitches have been observed on the planet, 

 first by Prof. Pickering on .\ugust 16, and subsequently several 

 times by both Prof. Pickering, Mr. Douglass, and Mr. Lowell. 

 Prof. Pickering calls them clouds. To .Mr. Lowell, appear- 

 ances thus designated are of two kinds. The one, certain 

 whitish, flocular patches not far from the pole, may possibly 

 be cloud ; for they present a peculiar aspect, not like snow, nor 

 yet like terra firina. No motion, however, has been seen in 

 them. The others are merely certain bright spots on the general 

 surface of the planet. These are not whitish, but yellowish, 

 and will probably do very well for the more arid, dried-up tops 

 of the land. They likewise do not move, and, furthermore, 

 show always the same appearance day after day as regularly as 

 their regions come round. Many of them were equally con- 

 spicuous at previous oppositions, and have been chronicled by 

 various observers. Their contours are neither shifty nor indis- 

 tinct, but as sharp-cut as those of any other region. 



Most suggestive of all Martian phenomena are the canals. 

 Were they more generally observable, the world would have 

 been spared much scepticism and more theory. They may, of 

 course, not be artificial, but observations made at the Lowell 

 Observatory indicate that they are. For it is one thing to 

 see two or three canals, and quite another to have the planet's 

 surface mapped with them upon a most elaborate system of 

 triangulation. 



In the first place, they were, at the season of writing, bluish- 

 green, of the same colour as the seas in'o which the longer ones 

 all eventually debouch. In the next place, they are almtst 

 without exception geodetically straight, ^upernaturally so, and 

 this in spite of tlieir leading in every possible direction. Then 



