January 5, 191 1] 



NATURE 



305 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.] 



Observations of Mars. 



In Nature of November lo, 1910, Mr. J. H. Worth- 

 ington gives his interesting observations of the fine 

 straight lines which he saw on Mars at Flagstaff, and 

 expresses his belief that these " telegraph wires " are 

 objective realities in the focal image. Although I have 

 not seen Mr. Worthington's paper, yet I shall reply to it, 

 basing myself on the accuracy of the abstract given of 

 it in the Journal of the British Astronomical Association, 

 vol. xxi., p. 130. 



Now Mr. Worthington's very brief experience of the 

 appearance of Mars during the few days spent at the 

 Lowell Observatory is necessarily outweighed by that of 

 an astronomer like Prof. A. E. Douglass, who spent 

 several years in the planet's study at Flagstaff. But what 

 was the conclusion of Prof. Douglass from his observa- 

 tions of the straight " canals," of which he saw more 

 than anyone else? That they are optical "illusions" 

 having " worked serious injury, to our observations " 

 (Popular Science Monthly, vol. Ixx., May, 1907). It would 

 be difficult to conceive a more decisive symptom of frailty 

 in the " canal " question than this surrender to truth of 

 its ablest exponent. 



In discussing my work rather than the collective 

 "vidence of great telescopes (of which my results form an 

 integral part), Mr. Worthington seems to show some mis- 

 apprehension in the very object of his criticism, for my 

 ■onclusions are identical with those arrived at at Lick, 

 Verkes, and Mount Wilson. Thus, in 1895, Prof. 

 Barnard, summarising his evidence with the 36-inch at 

 Mount Hamilton, said : — " No straight, hard, sharp lines 

 were seen on the continents, such as have been shown in 

 the average drawings of recent years " (Monthlv Notices, 

 R.A.S., vol. Ivi., January, 1896,' p. 166). On "September 

 21, 1909, I state that " those geometrical spider's 

 webs ... do not exist" (Journal of the British Astro- 

 nomical Association, vol. xx., p. 141). A fortnight later 

 Prof. Frost telegraphs : — " Yerkes telescope too powerful 

 for canals." Lastly, on January 3, 1910, Prof. Hale pro- 

 claims " the perfectly ' natural ' appearance of the planet " 

 in the 60-inch reflector, by far the most perfect and 

 powerful instrument ever made, " and the total absence 

 of straight lines " (Journal of the British Astronomical 

 Association, vol. xx., p. 192). 



It would thus appear that Mr. Worthington is perhaps 

 attempting to revive the old controversy on the relative 

 merits of large and small telescopes. But that question 

 has been settled long ago, so that any attempt to renew 

 It can no longer deserve serious consideration. The over- 

 whelming superiority of large instruments has been often 

 demonstrated on double stars, for the two discs seen in 

 a great aperture will be blended, by increased diffraction. 

 Into a single mass of light with an 18-inch ; and, as the 

 smaller star is observed to revolve in perfect harmony 

 with Newton's law, there can be no doubt whatever as to 

 its objective existence. The same fundamental principle 

 holds good for planetary detail. Two contiguous, 

 irregular, bright spots on Mars in a 33-inch will appear 

 as a single round spot in an 18-inch. Hence delicate 

 •>bjective markings, which are quite plain in large glasses, 

 annot be defined at all with inadequate instruments, and 

 his well-known rigid demonstration establishes for ever 

 he hopeless inferiority of small telescopes. 



The advantage of great objectives I have further shown 

 ^n Mars when stating (December 23, 1909) that the geo- 

 netrical network vanished in perihelic opposition of the 

 •>!anet. while much more delicate detail was quite plain 

 Journal of the British Astronomical Societv, vol. xx., 

 p. 141). On September 20, 1909, under perfect seeing, I 

 can discover no straight lines, but draw Lacus Moeris as 

 ^ vast shading, and Deltoton Sinus triple (letter to 

 >chiaparelli, dated September 21, 1909). A fortnight later 



NO. 2149, VOL. 85] 



the same region of Mars is photographed at Mount Wilson, 

 and Lacus .Moeris comes out likewise as a vast shading, 

 while the triple structure of Deltoton Sinus is also con- 

 firmed. On November 3, 1909, at Flagstaff, the " lake " 

 is missed (although covering fully one-sixth of the diameter 

 of the planet), and Deltoton Sinus appears single, while a 

 host of lines furrow the surface (Journal of the British 

 Astronomical .Association, vol. xx., pp. 376-7). But the 

 fact that straight lines are drawn when more delicate 

 detail, confirmed by photography, is missed, constitutes 

 another proof, not only of the inadequacy of the 18-inch 

 as compared with the 33-inch, but also of the inanity of 

 the " telegraph wires." 



Yet my position in the " canal " question should not be 

 misunderstood. If by " canals " be meant straight lines, 

 then I think the "canals" do not e.xist ; if we mean 

 irregular, more or less streaky markings, then the 

 " canals " exist. Of course, it would be utterly illegiti- 

 mate to speak of genuine canals on Mars. But in the 

 positions of Schiaparelli's lines I often saw, with the large 

 telescope, either (a) complex, irregular, knotted, or wind- 

 ing bands : or (b) jagged, isolated, dark sf>ots ; or (c) 

 indented edges of differential shadings. Under good see- 

 ing, the irregularities of these objects were held steadily 

 from five seconds to several minutes. From my experi- 

 ence of the " canals " since 1894, with various apertures, 

 I am led to account for the single and double straight of 

 lines of Schiaparelli as follows : over the objective sub- 

 stratum of irregular, sinuous corrugations diversifying the 

 Martian surface, a tired eye will discover by flashes a 

 geometrical appearance. Impressions of single lines will 

 fleet now and then either over a narrow objective streak 

 or over the jagged border of a half-tone, while double 

 parallel lines will flash in the position of a broader band. 

 But, as pointed out by Mr. Maunder, the straight lines 

 (which, so far as my evidence goes, are usually glimpsed 

 severally, and not collectively) are merely optical summa- 

 tions of groups of minute irregularities beyond the reach 

 of the instrument used. Prof. Lowell may justlv fee! 

 proud upon having succeeded where all his predecessors 

 failed, and upon having photographed the irregular streaks 

 of Mars by ingenious methods, devised at his observatory. 



A new notion was recently introduced in science bv the 

 "born-good" and "born-bad" air of some localities; 

 but the splendid results of Dawes, Lockyer, Burton. 

 Green, Denning, and others in the British Isles (a country 

 most unfavourable to telescopic work), prove that the 

 difference between the best and worst observing stations 

 is largely a difference of duration of good seeing. Trans- 

 parency of air, which is indispensable in detecting faint 

 stars or nebulae, seems to be of little moment in planetarv 

 detail. When minute Martian irregularities, bevond the 

 reach of an 18-inch at Flagstaff, are held steadily near 

 Paris with a 33-inch ; when such detail is corroborated 

 bv the unanswerable testimony of photography ; and when 

 the blue cap of Saturn is a most conspicuous feature at 

 Meudon a whole year before the recent Solar Congress, 

 W£ are bound to admit that anv point on the earth's 

 surface may give us short spells of perfect seeing. 



E. M. AXTONI.^DT. 



Paris, December 28, 1910. 



Sir Ray Lankester's Book on the Okapi. 



Sir Harrv Johnston is wrong in suggesting (Nature, 

 December 15) that the incompleteness of my monograph 

 of the okapi is due to the " financial control " (pre- 

 sumably he means the trustees of the British Museum) 

 disliking the expense of publishing a volume of text. The 

 full expenditure required was approved bv the trustees 

 when I was director of the museum. The absence of 

 any further text than that which accompanies the plates 

 and figures in the volume, as issued, is solely due to the 

 fact that I have not provided such further text. 



It would have been better to call the book " Contribu- 

 tions to a Knowledge of the Okapi " rather than a 

 " monograph " of that animal, since although it is in 

 the strict sense a monograph, it does not profess to give 

 (as Sir Harry Johnston seems to think that word implies) 

 a risumi of all that is known and has been written on 



