248 



KNOWLEDGE. 



[NOVKMBEF, 1903. 



the Hour-Glass Sea— always the most conspicuous, and 

 often the darkest, area oil Mars— in which the heavy 

 shading of that great "sea" is shown reduced to a pale 

 triangle, bound by " very black " lines.* Were this an 

 isolated case it might have been argued, with some 

 glimmer of probability, that the limiting "canals" were 

 real objects. But the appearance shown on Fig. 3 is only 

 a clearer representation than usual of a constantly recur- 

 ring phenomenon, since the darkening of the Martian 

 "seas" near their " shores " has been invariably one of 

 the leading features of Schiaparelli's delineations. 



Such a systematic intensification of the margins of the 

 dark spots, implying as it does the incongruity, even if it 

 be the only one of nomenclature, that the seas of Mars are 

 themselves bounded by canals, cannot correspond at all to 

 objective markings of the surface. That the intensity of 

 the grey spots is far from being uniform no one will 

 deny ; but to maintain that real differences of albedo so 

 manage their distribution as to imitate exactly the pheno- 

 mena of contrast, is to deny the weight of philosophical 

 Iirobabilities which have all the force of practical 

 certainties. 



These conclusions may now be checked by deduction. 

 If due to contrast, the marginal " canal " ought to be 

 sharply bounded on the outside, but to shade off more 

 gradually into the darker expanse beyond ; and it is note- 

 worthy that this corollary is in exact agreement with 

 Signor Schiaparelli's experience, since, speaking of the 

 " canal " limiting Syrtis Major on the following side, he 

 says that " along Aeria, it was better defined to the right 

 than to the left,"t or better on the bright side than on the 

 dark one. 



The apparent intensification of all indentations of the 

 Martian " coasts " is another inference from our propo- 

 sition, and is equally in harmony with experience. Let M 

 in the annexed Tig. 4 be a grey area, whose border, E S, 

 is exalted by contrast into the familiar black " canal " 



FiQ. 4 — Illustrating the Effect of Contrast in enhancinj; the 

 Darkness of the Indentations of the Martian Coasts. 



appearance ; and let us now consider the influence of 

 position on the apparent darkness of a dusky triangle, 

 having the same albedo as the dark spot M. As long as 

 our triangle remains outside the illusive " canal " snare, as 

 at A, it is, of course, indistinguishable from the general 

 duskiness ; but if its base coincide with the limits m n of 

 the grey spot, as in B, part of it will be immersed in the 

 intensification ; and if again the triangle be turned by 

 180^, the line m n o, playing the part of a hinge, as at C, 

 a larger proportion of its perimeter is exposed to contrast, 



* "Lince . 

 ^ Ibtd.,-p 7 



molto nere." Memoria Sesta, p. 74. 



and it will be cast at once into blackness. But what, may 

 we ask, will be the observer's impression on the darkness 

 of the indentation? Prompted by a zeal for detecting new 

 features, and scrupulously recoi'ding every one of his 

 impressions, he will be a little biased in favour of tracing 

 to an objective source all the facts revealed by his 

 exhausting scrutiny. He will not hesitate to consider the 

 intensified estuary as corresponding to a real difference of 

 tint ; and areography will be enriched forthwith by the 

 discovery of a brand new oasis. 



Our apparent knowledge of Mars thus always exceeds 

 our real knowledge, and this conclusion may be confirmed 

 by further considerations. When a disc representing the 

 appearance of the planet, without canals, is long examined 

 in ordinary sunlight, the law of contrast causes the 

 borders of the continents to appear fringed with a filiform 

 whiteness, such as has been experienced by all Martian 

 observers. In addition to this, however, the eye will 

 detect a duller and much broader intensification of the 

 " coasts," which, striking its roots in contrast also, runs 

 parallel to, and at a distance from, the outline of the 

 " Maria." The generally uniform albedo of the ruddy 

 deserts is thus also shown to apipear affected by physio- 

 logical vagaries ; and the unguarded observer, who 

 cherishes the objectivity of his discoveries, will either lay 

 stress on the brightness of the bordering lands, or insist 

 on the duskiness of the adjoining wilderness. But the 

 important point here is that the limit of the two tints is 

 often raised to a canaliform darkness — a conclusion which 

 justifies in some measure* Mr. Lane's theory that " the 

 mere shape of the oceans of Mars is sufiicient to give rise to 

 the appearance of the complicated system discovered by 

 Schiaparelli."t 



" Canals " are thus artificially developed which happen 

 to lie in the same positions as some of those discovered at 

 Milan. If the " coast " is straight (Aeria), the concomitant 

 " canal " is also straight (Phison) ; if the " coast " is curved 

 (Libya), the " canal " is also curved (Nepenthes) ; and if 

 the dark spot be oval (Solis Lacus), the bordering '■ canal " 

 (Ayathodsemon-Phasis) will run concentrically with the 

 outline of its objective generator. Whether this constitutes 

 a complete explanation of the '" canals " in question or not 

 it is scarcely wise to decide ; but it seemed interesting to 

 call attention to such a remarkable agreement between 

 physiological necessities and the facts of experience. . 



It now remains to consider the effect of contrast on a 

 dusky streak, such as the cigar-shaped Mare Cimmerium, 

 w'nose broadest end evaporates into half-tones. Fixity of 

 gaze should enhance its edges and brighten its interior 

 into a cometarv impression, exactly as seen by Schiaparelli. J 

 Then again the narrow Sinus Sabseus should also present 

 itself with a lighter interior, and the fleeting visiliility of 

 Xisuthri Eegio is a literal corroboration of this statement. 

 Scheria Insula in 1882, and Sirenia in 1892, furnish 

 us with kindred examples. But this is a phenomenon 

 which, according to Schiaparelli himself, is intimately 

 related to gemination ; and it is ob\T.ous that, by the 

 forced enhancement of their edges, all lakes§ and all 

 broad objective streaks or " canals " will a]>pear duplicated. 

 And thus, by a mere enquiry into the laws of contrast, the 



* Of course, contrast may account for such "canaU" running 

 parallel to the "coasts" a long way inwards; but it is incompetent 

 to explain " canals " forming an angle with them. Hence Mr. 

 Lane's theory is only partly confirmed by contrast. 



t Knowledge for November, 1902, p. 250. 



J Cimmeria Insula, in 1882. 



§ The long examination of a small dusky eclipse tends to double it 

 into round spots. 



