June i6, 1910] 



NATURE 



473 



1 iius it is a well-known fact with us that the main mark- 

 ings of a disc may come out sharp, while the delicate 

 ones are obliterated by a blur which otherwise eludes 

 detection. This applies as much to photographic as to 

 visual results, and it is this defect that a reflector intro- 

 duces. Another optical mistake, which has latterly been 

 hailed as showing that the lines are not lines, but a series 

 of dots, was made the other day in France. The observer 

 saw perfectly correctly, but one with knowledge of the 

 optics of a telescope in our air should have known that 

 the effect observed was the inevitable result of using an 

 aperture which the seeing did not warrant, as he could 

 easily have assured himself by looking at the shattered 

 rings in the synchronous image of a star. Even in our 

 far better Flagstaff atmosphere the best results are got 

 by diaphragming the aperture down. 



In photography we cannot diaphragm down to advantage 

 because we need the light, and this is one reason why 

 photographs cannot rival an expert eye. Visual observa- 

 tions conducted by an eye fitted by nature, and trained by 

 experience, must always surpass the best the camera 

 can do. 



One reason for this resides in the fact that the eye 

 registers its impression in the twentieth of a second, while 

 the plate takes forty times as long. The result is that 

 the planet's presentments in its bad moments are super- 

 posed upon its good ones to a composite photograph ' of 

 the whole, not unlike that got from a similarly merged 

 company of doctors where all individuality is lost in one 

 inane smile. As such well-meaning imbecility- does not 

 do justice to the planet, its exposure-time must be shortened 

 to the limit of effect. 



For a like reason the out-of-focus images of what by 

 courtesy is called the achromatic telescope must be sup- 

 pressed. So what the new process does is to mono- 

 chromatise the light as nearly as possible. This is accom- 

 plished by a colour-screen, and a plate sensitised in accord 

 with it. Then at the moment of exposure every precau- 

 tion is taken that all movement shall be as nearly nil as 

 can be secured within the instrument itself, and in the 

 air without it. Lastly, he who would photograph the 

 canals most successfully must first have seen them, that 

 he may know when his opportunity arrives. 

 , Planetan,' photography is not intended, nor is it destined, 

 to supersede visual observation. Research on the planets 

 must rest in future, as in the past, on the ultimate power 

 of the eye and of the brain behind it, a useful adjunct in 

 such investigation, whether this take the form of tele- 

 scopic, spectroscopic, or other perhaps new line of inquir>'. 

 ^ : in certain ways the sensitive plate may supplement the 

 -a. Position is one of these, contrast another. For 

 eye to place in their proper posts all the markings of 

 1 :r.ulti-featured disc in the short time at its disposal is 

 vell-nigh impossible task. The film registers them at 

 - in siUi. Values are another thing the photographs 

 :J out clearly. They exaggerate contrast, it is true, 

 compared with the eye : but this is no detriment. 

 her the reverse, for it furnishes a greater scale for 

 ~urement. 



n looking at the photographs two things must be borne 



-nind. One is that the irregularities due to the grain 



he plate must not be attributed to the images. Thus, 



"n the limits set by the grain, the lines on Slars show 



nes, not as a patchwork. This is perfectly apparent 



1 they are carefully scanned. When we consider that 



original images are only /; mm. in diameter we realise 



strain of lantern exhibition. Even so they are 



-Unified 200 times in the taking. They are then further 



enlarged on the slide, and lastly thrown greatly increased 



lupon the screen. The wonder is that thev stand this lime- 



! light publicitv- at all. 



'\ The second point is that we are not dependent on them 



for our minute knowledge of the planet. A good eve 



•ed to the subject sees at least ten times as delicately 



the film ; but it must be an eye suited to planetary 



'<s which is quite a different eye from that good at 



: satellite or nebula detection. It is very important to 



I'rmber this, for not only is there a physiologic reason 



'^' it, but mistake of it is often made in high quarters. 



•=n an observer records a polar flattening as twice and 



' times w-hat hydrodynamics permit, his forte lies else- 



rf- than in planetary- research. 



XO. 2120, VOL. S"?! 



Three planets will now show you their presentments, 

 Mars, Jupiter, and Saturn. 1 was minded at first to omit 

 Mars, passing by this old acquaintance with a nod, but 

 so great have 1 found the interest in him here as else- 

 where that he has been put beside the others. 



.As an example of the delicacy of the detail to be 

 described on him, not only by the eye, but in the photo- 

 graphs, may be instanced the sight of one of the many 

 vicissitudes of his changeful year, which suddenly appeared 

 one day when least expected. The event was the first 

 frost of the season in the Antarctic regions of Mars, 

 detected visually at Flagstaff on November 16. The patch 

 was at once photographed, and is plainly apparent on the 

 plate. To chronicle thus the very weather on our neigh- 

 bour will convince anyone that interplanetary communica- 

 tion has already begun, and that, too, after the usual 

 conventional manner of ordinary mundane greetings. 



My next mention shall show you the pitch of precision 

 to which measurements of these little prints can attain. 

 It is well known that the south polar cap of Mars is not 

 centred on the pole, but lies some 6° off it, in longitude 

 20° or thereabouts. When the images showing the cap at 

 two different longitudes were measured, the measures re- 

 vealed distinctly the excentring of the cap, and even 

 registered with some accuracy its amount and position. 

 When we reflect what this means, it looks as if Mr. 

 Crommelin's belief that areologv^ would stand indebted to 

 the photographs for help in its geodetic survey is in a fair 

 way to be realised. 



It would be possible in these photographs to take you 

 on many a journey to that other world, but one such inter- 

 planetary voyage must suffice. This shall give you sight 

 of the great new canals that appeared last September in 

 a region of the planet where no canals had ever showed 

 before. To begin with, you should know that the lines 

 you will see are certainties, not matters admitting of the 

 slightest question for all their strange regularity, and so 

 seen by all those who, from the most prolonged and careful 

 study, are qualified to speak. Schiaparelli described them 

 as looking as if they had been laid down with rule and 

 compass, and not only I, but all of my assistants, have 

 seen them thousands of times the same. Nor are they 

 near the limit of vision in our air, which sometimes sets 

 the planet against the sky as if etched in a steel engraving. 



In the second place, the technical word " canals " does 

 not mean ditches dug, but artificially fertilised strips of 

 countr>- to which the water from the polar cap is led by 

 some mechanical means. We have proof of their 

 artificiality from the fact that they develop latitudinally 

 down the disc from pole to equator after the cap begins 

 to melt, for on a body the surface of which is in equil- 

 ibrium, as with Mars, neither water nor any other sub- 

 stance could take this equatorward course unless it were 

 intelligently conducted. What the conduits that lead it 

 may be like we ignore, for all we see is their effect on 

 vegetation. 



Lastly, the organisms of Mars can hardly resemble men, 

 which opens up for them unknown possibilities of intelli- 

 gence and renders them really interesting. 



On September 30 last, when the region to the east of 

 the Syrtis Major came round into view again after its 

 periodic hiding of six weeks, due to the unequal days of 

 the earth and Mars, two imposing canals were seen lead- 

 ing up from the Syrtis to the south-east, which had not 

 been there at the preceding presentation. Research showed 

 that not only had they never previously been seen, but 

 that they could never have existed as such before. The 

 long and full records of the observatory, extending over 

 fifteen years, made it possible to be absolutely sure of this. 

 Yet these canals, with several subsidian.' ones, fitted into 

 the general canal system as if they had always made part 

 of it. 



Not only was their coming into existence established 

 by the drawings, but the photographs of previous years 

 testified to the same unheralded advent. By comparing 

 the drawings and photographs made at the same epoch 

 the oneness of the two becomes evident, while the change 

 of both with the Martian seasons is clearly portrayed. 

 Thus we have actually witnessed a " canal " called into 

 being by the life existent at this moment on the surface 

 of Mars. 



Turning now to Jupiter, we find a completely different 



