NoVEMnER, 1902.] 



KNOWLEDGE 



251 



to go up to the drawingf to make sure iu my owu mind 

 that I had uot put a line there by mistake. When first 

 looked for, very steady gazing is needed to see them at all ; 

 in faet, in my case it required two minutes staring before 

 I could perceive the slightest fleeting indication. If 

 another attempt be made, say next day, they are seen 

 mueli more easily than at the first attempt, and the task 

 of seeing them becomes easier every time, until now with 

 me I can scarcely look at the drawing witJiout seeing some 

 one or two. The first time these canals are seen they 

 appear as broad, misty, ill-defined bands, which easily 

 change their places, but when a little practice has been 

 liad in seeing them they appear as firm hard lines, 

 indeed, as Mr. Lowell puts it in sjieaking of the real 

 canals, " like a steel engraving." In fact, I .should say 

 from what I have been able to gather resjiectiug the 

 appearance of the canals on the jilanet, it is easier to 

 see canals on a blank drawug like Fig. 1 placed at 

 a distance of 20 feet from the eye than to see them 

 on Mars. 



The above-described experiment can be performed by 

 anyone having a blacklead and a piece of ordinary rough 

 drawing paper. It must not be expected tliat everyone 

 will be able to see these canals on the drawing, since 

 everyone who has looked for them has not seen them on the 

 planet, but two at least out of every three persons should 

 be able to see them with steady gazing, if the diagram is 

 of suitable size and idaced'at a suitable distance. The 

 one used by me was 3^ inches in diameter, and was placed 

 at a distance of 20 feet iu not too good a light. 



It may be said that even though the ordinary canals 

 Could be produced by an optical delusion, such a com- 

 lilicatcd system as that of Elysium could noc be the 

 product of such a cause. All that is needed to produce 

 an exact replica of this district is that an oval patch of the 

 ilrawing should be made slightly lighter in colour than 

 tlie surrounding paper, when contrast will at once cause 

 the ajiiiearunce of a circular canal surrounding it, from 

 wliich the other canals branch. The side of the planet 

 jiictured in these drawings is not the only one which I 

 liave made use of. In faet experiments made with drawings 

 of the other side were even more successful, and the 

 iiettifl'' oi the canal known as the Hydraotes was at times 

 truly startling. 



It thus appears possible, since two systems may be 

 seen, one on Maps, and the other on a drawing, which are 

 not only anaio^^us but identical iu every particular (since 

 any two observers difter as much as tlie drawings here- 

 with reproduced), one of which is certainly produced by an 

 optical delusion, that tlie other, viz., that seen on Mars, 

 may also be due to the same cause. The facts that the 

 canals are not best seen when the planet is nearest, and 

 that canals have been seen on other planets, seem to point in 

 the same direction. The fact that the directions of the 

 canals change with the Martian seasons need be no 

 hindrance to the theory of tlieir ojitical production, since 

 if they are so produced their direction and degi'ces of 

 visibility depend on the shape of the Martian oceans, and 

 since these change with the seasons, the canals will change 

 also. It may be remarked that by not suggesting canals 

 to the subjects of our experiments, we have put them in a 

 more disadvantageous position for seeing them than 

 anyone besides Schiaparelli has been in, since later 

 observers not only heard of the canals but studied 

 Schiaparelli's maps, and so aided any optical delusion 

 which might exist. The above results, therefore, would 

 have been fairly conclusive even if canals had been 

 suggested. 

 Thus it would appear that those gentlemen who have 



seen the canals have, with the best intentions, been 

 deceived by a most peculiar and almost incredible optical 

 delusion— a delusion which has given rise to a system so 

 complicated that no one has hitherto attempted to prove 

 that the whole appearance was from beginning to end 

 attributable to this cause, although many have asserted 

 that such was the case. 



[The first suggestion of the idea thus worked out by 

 Mr. Lane occurred to me in 1882, when I noted how many 

 of the Schiaparellian canals were prolongations of what 

 other observers had drawn as indentations on the coast 

 lines of Mars ("Observatory," Vol. V., pp. 13(3, 1:]8). 

 Later, in ISiH, T made some experiments on the limits of 

 visibility for dark markings on a bright background 

 (Knowledgk, 180-4, November, p. 249), and incidentally 

 noted, when irregular forms were at such a distance that 

 the minutest details of their irregularities were too small 

 to be separately defined, and yet were large enough to 

 produce some impression, that it was easy to interpret 

 such irregularities as parts of a network of straight lines. 

 r further noted that under such circumstances, i.e., when 

 markings were too narrow or too small to be fully and 

 distinctly defined, but yet were sufficiently large to be 

 indefinitely glimpsed, the rendering in the case of narrow 

 markings, however winding, broken or irregular, was that of 

 straight lines ; but in the case of compacter objects the 

 rendering was of round dots. And narrower objects could 

 be discerned as straight lines than as dots. Hence I ventured 

 to foretell (Knowledge, ISO-l, November, p. 2-52) that 

 the Schiaparellian canal system would be followed by the 

 discovery of a system of " lakes " ; a prophecy almost 

 immediately fulfilled at the Lowell Observatory, by the 

 detection of the " oases." 



Acting on the suggestion of Mr. Lane's letter, and by 

 the kind co-operation of Mr. J. E. Evans, headmaster of 

 the Eoyal Hospital School, Greenwich, I have cjuite 

 recently subjected a number of drawings of Mars — free 

 from canals — to boys in that school, for them to copy. 

 The result was striking. Four out of five drew no canals, 

 but the remaining fifth supplied them. And it was clear 

 that this was directly a question of their distance from 

 the drawing. Boys near the drawing saw too well and 

 distinctly to imagine spurious lines. Boys at a great 

 distance could only perceive the leading features of the 

 drawing. But those at mean distance, by whom the minor 

 details were imperfectly perceived, in many cases rendered 

 these by straight narrow "canals." 



Yet I am not prepared to accept Mr. Lane's conclusion 

 ({uite as he puts it. Some of the " canals " seem to have 

 heen detected with so low a power that their full and dis- 

 tinct definition would be well withiu the power of large 

 and well-placed telescopes. Hence my own view of the 

 "rendering" or "interpretation" of undefined objects 

 would not enter into their case. Nor do my own experi- 

 ments quite confirm his as to the canals presenting them- 

 selves to the imagination, unless there are minute markings 

 present — however unlike the canals — to afford a sort of 

 basis for them. E.g., stippling lightly the general surface, 

 but leaving Elysium free, was quite enough to create a 

 polygonal system of canals around Elysium. But though 

 the stipple dots were too small to have been separately 

 and clearly seen at one-twentieth the distance, they or 

 their equivalent had to be present, or no " canals " would 

 have been seen. 



Nevertheless, Mr. Lane's letter puts in a new and 

 striking light a factor in the problem of Mars which, 

 although almost entirely neglected hitherto, will have to 

 be taken into full account in the future. — E. Walter 

 Maunper.] 



