>oo 



NA TURE 



[September 20, 1894 



On July 5, 1S90, at loh. Pacific standard time, a 

 sketch by Prof. J. E. Keeler, with the 36-inch, showed a 

 narrow, ellipticai, white spot from 15 to 20 long, pro- 

 jecting northward at a slight angle with the line of the 

 terminator. Half an hour later the spot was within the 

 disc, bat still visible as an oval white patch on a darker 

 background. The following day (Sh. 3m.) Prof. Holden 

 saw a projecting spot curved upwards and nearly meeting, 

 and the smaller projecting spot some 2 farther towards 

 the south. The lower spot changed very considerably 

 its shape during the time of observation, about an hour, 

 and was observed to be always situated at the end of a 

 long bright stripe of the surface of the planet which lies 

 north of Ueuteronilus. 



A second case may be taken from the observations of 

 Prof. Hussey and Campbell, made at the opposition of 

 1S92, on July 1 1, with the Lick instrument. They record 

 that a most striking one (prominence) was visible when 

 the observations began at I2h. 15m., and remained con- 

 stantly in view for about two hours. Its shape changed 

 a great deal during that time. At I3h. 25m. it was 

 unusually prominent, and its outer e.xtremity was per- 

 ceptibly bent upward toward the south polar cap. On 

 July 13 these observations were duplicated ; the southern 

 one of the two projections presented the hooked or bent 

 appearance most strongly at I4h. 35m., just as it was 

 seen two nights earlier at I3h. 25m. Allowing for the 

 longer rotation period of Mars, the same point on the 

 planet was under observation on the two nights. 



.\ somewhat indirect reference to these bright projec- 

 tions made by the .Arequipa observers is included in the 

 statement made by Prof. \V. H. Pickering, that "clouds 

 have on several occasions been observed to project 

 beyond the terminator and also beyond the limit, thus 

 confirming the observations made at the Lick Obser- 

 vatory." 



Licsides the above-mentioned observations, inserted to 

 serve as samples of what has been seen, many more, by 

 different observers, might be given, but they are all of 

 the same type, and undoubtedly describe the same 

 phenomena. One principal fact about them seems to be 

 that although their shapes undergo distortions of all 

 kmds, due to the different directions of the illuminating 

 source, their mean positions seem to be at all times more 

 or less constant. 



.■\5 they appear beyond the terminator, not too far from 

 it and within the limb, and are brilliantly illuminated, 

 the natural conclusion to draw from this is that ihey 

 must either be the tops of high mountains lighted up by 

 the sun, or clouds at a high altitude in the Martian 

 atmosphere, rendered bright by the same source. The 

 latter suggestion, which, in the face of the most recent 

 facts, does not seem to have much weight, was put fur- 

 ward by i'rof. W. H. Pickering, and their height above 

 the surface of Mars was measured to be at least twenty 

 miles : more recent measures indicate that these 

 estimates are far too high. That they may be, and 

 most probably are, mouniain tops, is the most general 

 explanation ; and I'rof. Campbell,' whose opinion 

 coincides with our own, says they are "due to 

 mountain chains lying across the terminator of the 

 planet, possibly covered with snow in some cases, and 

 in others not necessarily so." 



The reasoning he adopts may be summed up as fol- 

 lows : (Jn July II, lSy2, the Larth was approximately 

 39,000,000 miles distant. With powers of 350 to 520 

 the equivalent distances were reduced to 110,000 and 

 75,000 miles respectively, distances equal to one-half and 

 one-third of that of our Moon from us. Now if, with the 

 naked eye, one can see at the terminator of our satellite 

 bright projections at a distance of 240,000, surely pro- 



' ''An Eiplanatirtn nf the Bright Proieclioni ob«rvcd on the Terminjilnr 

 of M.ir«,"' by W. W. CiropbelL /*. Ailr,)naiiiicai Soiitty of the i'an'fit, 

 vol. *i. No. .^. |». 1 J J. 



NO. 1299, VOL. 50] 



jections, if any, at much lesser distances should be visible 

 on the Martian disc. 



If they be due to mountains, a small calculation has 

 shown that they need be only of a moderate height, 

 entirely comparable with those on the Earth and Muop. 

 The figures computed to represent the height of the 

 hills, satisfying the July observations, represented an 

 altitude a little more than iSg miles. 



A well-observed fact, which strengthens the mountain 

 theory to a certain extent, is the presence of extremely 

 brilliant star-like points which have appeared both on 

 and off the snow-cap. If these are really mountain- 

 tops, they should be visible always with suitable illu- 

 mination, for when seen on a background of snow their 

 height should enable them to catch all available light for 

 reflection ; and, secondly, when observed on darker 

 surroundings (as when the snow serving as a back- 

 ground has melted', their height would still serve the 

 same purpose, besides preserving for them their snow- 

 capped peaks. The constancy in position of these spots 

 shows that they are rigidly connected with the surface, 

 and not due to the atmosphere, unless they be looked 

 upon as stationary clouds or mists, which does not seem 

 likely in the Martian atmosphere. Mr. Lowell this year 

 has observed and measured some, the positions of which 

 correspond with the measurements made by Green in 

 1S77. 



In Prof. Holden's mind the mouniain theory seems to 

 be thoroughly conclusive, for at Mount Hamilton, night 

 after night, and even month after month, the prominences 

 on the planet appear in the same longitudes and lati- 

 tudes, insomuch that a map of some of the chains is in 

 preparation. 



The positions of these brilliant spots on the globe of 

 Mars, just referred to, lie much nearer the South Pole 

 than those which have appeared as projections. This 

 shows that we must not look upon the Martian surface 

 as very llat, but as one studded with hills and dales, if 

 we have such indications of unevenness as we are led to 

 believe. 



It may be remarked here that at Mount Hamilton 

 and at Nice no bright prominences have been seen out- 

 side the limb, the only observations of such a nature 

 of which we are aware being those of Martian clouds 

 at Arequipa, where, Prof. Pickering states, " clouds have 

 on several occasions been observed to project beyond 

 the terminator and also beyond the limb." 



In considering the visibility of mountains at the ter- 

 I minator and at the limb, certain important points must, 

 as Prof. Campbell says, be taken into account. 



In the first place, 10 obtain the greatest " seeing 

 eiTect' at the terminator, it is not so much the height of 

 the mountain in question, but the length of its chain that 

 IS the chief function. On the other hand, a mountain .it 

 the limb is seen simply by virtue of its heii^hl above the 

 general surface, the Iciigllt of the chain in this case bein^' 

 entirely eliminated. It must not be forgotten, however, 

 that we view Mars from the earth, and not from the sun. 

 This fact, combined with the different positions of the 

 planet's axis at the times of opposition periods, accounts 

 for the innumerable ways under which mountain chains 

 can be illuminated, rendering them sometimes visi'.-le 

 and sometimes invisible, according to the conditions in 

 vogue. Kor instance, in KS(;othe mountainous part ob- 

 served was in the region a little 10 the north of Tempe 

 (lat. 40 N., long. 45 ). In lSt)2 the projections were 

 chietly observed about the region of Noachis (lat. 30 

 and 50' S), two small ones being remarked at 25' N. Lit. 

 At Nice projections were noticed in approximately the 

 same position, and in additional 30 S. lat. and 220 long. 

 to the south of Ilesperia. 



Such, then, are some of the facts and deductions to 

 which a discussion of the observations of these promin- 

 ences, made up till now, has led us. There is, no 



