November, 1903.] 



KNOWLEDGE, 



247 



car iuability to deal with this obscure question. But, as 

 ably pointed out by Mr. Maunder in the exposition in this 

 number of Knowledge of his most valuable experiments, 

 we have now reached a stage where we are certain of the 

 existence of some dusky streaks, and justly suspicious of 

 the reality of others. The " canal " named Cerberus, for 

 instance, is often as dark and definite as a " sea " ; its 

 objectivity is thus above cjuestion, unless, indeed, we 

 come to doubt the very existence of large dusky areas on 

 Mars. Several other "canals" — say one-third of the 

 whole number — have also more or less strong claims to 

 reality ; although some of them are only the boundaries 

 of the half-tones to which Mr. Green has called attention, 

 while others, in accordance with Mr. Maunder's theory, 

 are an integration of visible minute, or still smaller, and 

 invisible, details. The philosophical importance of Mr. 

 Maunder's experiments lies in the demonstration that, in 

 order to appear furrowed with " canals," the Martian 

 deserts require only an irregular distribution of any kind 

 of minute grey markings. We need, therefore, no longer 

 believe that " a Martian would be fifty-fold more efficient 

 than man, whether in digging canals, or in other bodily 

 occupation";* and thus, for the suspicious achievements 

 of the hardy canal digger, modern science lias fitly 

 substituted the more rational interpretation of ^physiological 

 principles. 



During the last opposition of Mars, in the early spring 

 of 1903, the writer was enabled to confirm part of Mr. 

 Maunder's theory for two " canals," the Oxus and the 

 Casius, both of which were seen composed of a congeries 

 of small dark spots, a1 the limit of visibility (see the 

 annexed Plate, drawings of April 6th, w = 341°, and April 

 lltli, cu = 260^). These observations were made with an 

 8^-inch reflector by Calver, magnifying 292 and 408 

 diameters, the excellence of whose mirror rendered possible 

 an abnormally sharji view of the " canal " Oxus. Instead 

 of uniting, as usual, Margaritifer Sinus to Arethusa 

 Lacus,t the Oxus ran, as in 1886, into Ismenius Lacus, 

 being very narrow and black towards the south, then 

 swelling out into a lake-like patch, and finally fading off 

 into Ismenius Lacus. Equally objective, though less 

 sharp, were the so-called " canals " Cerberus, Cyclops, 

 Hades, Eurotas, Nilokeras, Nilosyrtis, Pierius, and Proto- 

 nilus ; while a weird black hook, curving out of Ismenius 

 Lacus in a southerly direction, also gave an overwhelming 

 impression of reality. 



Having thus admitted the partial objectivity of the 

 Scliiaparellian " canals," though carefully avoiding to 

 consider them as artificial watercourses, we must now give 

 our reasons for refusing to accept them in their entirety. 

 Doubt arises here from the fact that the Milan observer 

 has seen subjective " canals " on Mercury also ; and that, 

 as shown by Mr. Lowell's planetary observ^^tions, and by 

 Mr. B. W. Lane's invaluable experiments, J the "canaliform 

 illusion" is a nonual physiological phenomenon. If, there- 

 fore, non-existent " canals," as harsh as the markings on 

 the moon, affect the discs of other planets, they are also 

 certain to attack the appearance of Mars ; and there must 

 be a limit beyond which the phenomena of the real Martian 

 " canals " are continued, or imitated, by the illusions of 

 prolonged eye-strain, if not of fancy. 



If we inquire into the relevancy of Mr. Green's inter- 

 pretation for some " canals," we shall find that it accounts 

 for one-half of the linear markings. Its principle may be 

 illustrated by a representative example. While in 1883- 



* Lowell, Mars, p. 20.5. 



+ For the identification of the markings see the Chart of Mars in 

 Knowlkdob for Noreinber, 1902, p. 202. 



J Knowiedoe for November, 1902, pp. 250-251. 



1884 Schiaparelli was seeing the region called Utopia as a 

 yellow triangular area, limited by black " canals" (Fig. \), 

 Mr. E. B. Knobel, f.r.a.s., one of our ablest authorities 

 on the planet, was seeing the same region intensely shaded 

 (Fig. 2). 



We are naturallv curious to know which of these two 



Fig. 1. Fig. 2. 



The Region Utopia on Mars, as seen iii 1883-1884 by Prof. 



SchiaparelU and Mr. Knobel. 



Illustrating the Instrumentality of Contrast in reducing a Dusky 



Shading into a Canal-girt Bright Area. 



appearances expresses more truthfully the actual con- 

 figuration of this part of the Martian surface. A little 

 consideration will render it evident that, since the dark 

 area seen by Mr. Enobel is not resolved into separate 

 dusky markings by Schiaijarelli, the Englishman's re- 

 presentation is more trustworthy than the Italian's- a 

 result which implies that the eye of Schiaparelli is afEected 

 by a strong personal equation, or a i)eculiar physiological 

 bias, which strains it to decompose dark sjwts into more 

 or less bright polygons, limited by black " canals." 



But contrast does not confine its action to the intensi- 

 fication of the boundaries of faint half-tones. Enjoying a 

 much greater generality, it affects the appearance of ^ all 

 definite markings of the surface. A mere glance thrown 



Fio. 3.— The Syrtis JIajor, us seen by Schiaparelli on 1883, June 4th.* 

 Illustrating the Instrumentality of Contrast in breaking up the 

 Intensity of a very Dark Area into a Pale ijhading limited by 

 Black " Canals." 



on Fig. 3 will suffice to corroborate this assertion. Here 

 we have to deal with an observation, by Schiaparelli, of 



* Memorip Sesta, PI. IV., Fig. 10. 



