250 



KNOWLEDGE. 



[November 1, 1894. 



Fio. 1. — Horscliel II. Strait, as seen bv Beer 

 and Mailler on October 1-tth and 19tli", 1S30. 

 From Fhnnmarion's ' Mars," p. 566. 



been on the side of the patient and keen-eyed Italian 

 astronomer. Each succeeding opposition has seen more of 

 his " canals" identified by other astronomers ; each con- 

 struction of a ne^y and more powerful telescope, each 

 enlistment of a fresh earnest and skilled observer, has 

 meant a further confirmation of his work. So that now 

 there is a bulk of evidence in favour, not merely of some 

 of Schiaparelli's " canals," but of his canal system as a 

 whole, by no means lightly to be set aside. 



The positive evidence has not, however, destroyed or 

 overcome the negative. Both still hold the field, and both 

 must be considered. The principal points against the actual 

 existence of the " canals," as represented by Schiaparelli, 

 may be summarized as follows ; — 



1, They are extremely narrow objects, approaching the 

 theoretical limits of visibility, even when Mars is at its 

 nearest approach. Thus a fine drawing reproduced in 

 Flammarion's great monograph on "Mars," p. 508, shows 

 " canals" of breadths not exceeding 004" or 0-05" of arc. 

 The two branches of a <Uiubleil " canal " in one part of the 



sketch are dis- 



tant from each 

 other only 0-25". 

 Nor is this all. 

 In his account of 

 his 1888 observa- 

 tions (maximum 

 diameter of 

 planet, 15-4"), he 

 states that in 

 a set of canals 

 on MiiJler Con- 

 tinent he could 

 make out, not merely the two banks of the canals, but also 

 " very small undulations in their two banks, which could 

 be distinguished from each other." 



2. The distinctness of some of these objects, though so 

 narrow, does not seem impaired by distance. Thus, in 

 the opposition of 1877, the Indus was lictUr seen by 

 its discoverer when the planet had receded a great 

 distance from opposition, and was very well seen when the 

 planet was only 5-7" in diameter, and the canal 0-2" in 

 breadth. 



3. The great divergency between the descriptions of 

 different observers. To take the one (and all important) 

 feature of breadth. In the opposition of 1890, when 

 Schiaparelli was observing " canals " down to a breadth 

 of 005", Holden and Keeler, at the Lick Observatory, 

 always saw the canals as dark, broad, somewhat diffused 

 bands. We may judge what is meant by " liroad bands," 

 for the record goes on : — " In bad vision they were drawn 

 in that way by Schaeberle also. Under good conditions, 

 however, the latter observer described them as narrow 

 lines, a second of arc or so in width." A second of arc 

 corresponded at this time to a minimum of (i ' of a Martian 

 great circle ; that is to say, to abou,t the breadth of 

 Herschel Strait, and very nearly to that of the Mare 

 Sirenum, the narrower end of the Maraldi Sea, or to 

 nearly double the breadth of the Nasmyth Inlet, or the 

 point of the Kaiser Sea, markings seen even by the 

 earliest observers. If Schaeberle could describe markings 

 of such dimensions — markings twenty times as broad as 

 Schiaparelli's narrowest canals — as " narrow lines," what 

 must have been the breadth of the " broad bands " of his 

 two colleagues "? It is clear that the phenomena observed 

 by the Lick observers were quite of a different order to 

 those recorded liy Schiaparelli. 



4. The greatness and suddenness of the changes remarked 

 in the "canal " system. The "gemination" or doublmg 



of the " canals " has been remarked " to take place in a 

 relatively short space of time, and by a rapid metamorphosis. 

 . . . Sometimes the metamorphosis has been completed 

 in the interval of twenty-four hours between two con- 

 secutive observations. So far as the observer could judge, 

 the phenomenon took place simultaneously along the entire 

 length of the canal doubled." Schiaparelli himself draws 

 attention to the strange and rapid changes taking place on 

 the planet, and remarks ; " Evidently the planet has fixed 

 geograi)hical details similar to those of the earth, with 

 gulfs, canals, &c., on an irregular plan. There comes a 

 certain moment and all this disappears, to give place to 

 these grotesque polygons and geminations, which clearly 

 represent approximately the former state; but it is a coarse, 

 and, I might say, almost a ridiculous mask." 



5. The "canals," when near the edge of the disc, are 

 apt to be represented as much straighter than they could 

 possibly be. 



G. To these difficulties may be added that at the very 

 time when to some observers the canal system was most 

 developed, others have sometimes only been able to perceive 

 the usual markings of the planet in their customary con- 

 figuration. 



How are we to explain these curious discrepancies ? 



First of all, many of these differences are to be explained 

 by difl'erences in " seeing" power, including in that term 

 not merely atmospheric conditions, but instrumental and 

 personal differences, such as the aperture of the telescope, 

 its defining power, the magnification employed, and the 



Fin. 2.-Dr 



.vings of Mars, by Dawes, in 1864-65. From 

 Flamiiinrion's " Mars," p. 187. 



keenness of sight and artistic skill of the observer. Two 

 illustrations may be given of these. In 1802 a number of 

 drawings by different observers were made of the De la 

 Rue Ocean. The observers best equipped with instruments, 

 and most favoured by observing conditions, recorded this 

 ocean to be marked by the presence of one, two, three, 

 or more islands. The better the conditions the more the 

 number of islands represented ; the smaller the aperture, 

 and the less the experience of the observer, the fewer ; so 

 that the drawings showed every variety of representation. 



