June 1, 1888.] 



♦ KNO^A^LKDGE ♦ 



181 



THE PLANET MARS. 



MAP of this planet is preparinir, which will 

 appear next month. The work of com- 

 parison between the many hunJreds of 

 drawinjrs of the planet available for stuily 

 lias taken a longer time than anticipated. 

 But the map will be ready now very soon. 

 In the meantime I woidd call the atten- 

 tion of observers to the excellent opportunity they now have 

 for studying the featm-e which Schiaparelli attributes to 

 " double canals." 



I have accepted as the best available explanation of the 

 observed a]jpearances, that the rivers on Mars observed 

 under different conditions account for all observed appear- 

 ances. 



First. If, as is probably the case in the winter of either 

 hemisphere of Mais, there is much cloud over a ^Martian 

 continent, the rivers on that continent would not be dis- 

 cernible at all. 



Secondly. If, as is probably the case, for some time before 

 each equinox the clouds clear away from a continent on 

 Mars but .still hang over the Martian rivers on that con- 

 tinent, they would cause the rivers to appear like silver 

 threads of exceeding fineness if Mars could be seen as he is. 

 But in a telescope even of great aperture the points of light 

 along the river would be seen as diffraction discs, each sur- 

 rounded by a ring of definite diameter ; and the combina- 

 tion of all the.se diffraction discs would form what would 

 look like a relatively bright streak bordered by two dark 

 streaks (corresponding to the daik spaces around each 

 diffraction disc). [The relatively bright streaks correspond- 

 ing to the bright rings would not be recognised as bright 

 streaks, being merged in the light backgi'ound of the Martian 

 continent.] 



Thirdly. When the clouds were cleared away from a 

 Martian continent, and also from the rivers upon it, which 

 must often be the case during ISIartian summer, the rivers 

 would appear like dark streaks — of course much broader 

 than the livei-s reall}' are, because the image of a point along 

 one of these rivers is not point-like, even with the most 

 perfect telescope. 



All that has hitherto been observed by Schiaparelli, 

 Perrotin, Thollou, and others corresponds with the theory 

 here advanced. (It was first advanced by me in the 

 Newcastle Weekly C/ironicle very soon after Schiaparelli 

 announced his startling discovery of the Martian double 

 canals.) 



What is now wanted is a series of observations of Mars 

 near the autumn of the northern hemisphere (on which 

 most of the " double canals " have been seen). Mars will 

 pass the equinox (autumnal for his northern hemisphere) on 

 or about August 6, and will be well placed for this 

 particular research during June and July. 



It will hardly be necessary to remind observers that they 

 should carefully try the effect of varying the aperture of 

 the telescope they may use. If the " double canals " are 

 phenomena of diffraction they would be best seen with a 

 certain aperture, such as would give to the dark ring round 

 the diffraction di^c of a star a diameter equal to from a 

 tenth to a twentieth of the diameter of Mars. If the space 

 between the " double canals " be found to correspond with 

 the span thus resulting for a given aperture, the diffraction 

 interpretation of these phenomena would be confirmed ; if 

 the space varied with varying aperture, and in accordance 

 with the known relations between the aperture of the object- 

 glass and the size of the diffraction disc, that interpretation 

 would be established. 



THE NEW ASTRONOMY.* 



ItOFESSOR L ANGLE Y (we hope we are 

 right about the title, but our author's title- 

 page mentit)us nothing which in England 

 wovdd be regarded as implying professorship) 

 gives as the rai'ioii d'etre for his book the 

 desire to reach those members of the com- 

 munity on whose support the endowment of 

 research chiefly depends. He has written, he says, not for 

 the professional reader (whatever that may mean — in 

 England professions are very various), "but with the hope 

 of reaching a part of that educated public on whose suppoit 

 he " (])resumably the " professional I'eader ") " is so often 

 dependent for the means of extending the boundaries of 

 knowledge." This vague purpose may be a sufficient reason 

 for the shortcomings of the book before us. Professor 

 Langley evidently has a very poor idea of " that part of the 

 educated public on whose support, etc." But whether this 

 be so or not, the mere idea of the endowment of research 

 has long since been made to " stink in the nostrils " of the 

 British public. Professor Langley himself has passed from 

 a fairly salaried position with splendid opportunities (of 

 which he has well availed himself) for independent research 

 to a position much better salaried, but without those oppor- 

 tunities. We propose, then, to examine his book with 

 strict reference to its worth, and without considering (what 

 in a different connection we would consider with enthusiasm) 

 his undoubted services as Director of the Alleghany Obser- 

 vatory to the caiise of <.)riginal research. 



In the first place, we note that " the educateil public on 

 whose support " he depends would seem to be regarded by 

 him as better able to judge appearances than so mere a 

 trifle as intrinsic value. Or it may, perchance, be his pub- 

 lishers, Messrs. Ticknor ife Co., of Boston, who suppose that 

 the public will be content with the weight of paper and 

 binding supplied them, without considering the amount of 

 information conveyed, or of new thoughts suggested. Be 

 this as it may, Professor Langley's book is amazingly heavy 

 for the number of pages it contains, and better suited for the 

 desk than the hand — save of the athlete to whom the 

 raising of 5G lbs. at arm's length is a pleasing exercise. The 

 cover positively creaks as it is opened, so stoutly and 

 strongly (and, alas! so heavily) is it built. Sterne objected 

 to the application of rule and square by the critic to the 

 books he may have to consider ; but in the case of the book 

 before us, such points as weight and structure force them- 

 selves upon the I'eader's — or rather the holder's — attention. 

 We find that '' Professor " Langley's " New Astronomy " 

 weighs rather more than Sir John Herschel's "Outlines of 

 Astronomy " and Mr. G'lodd's " Story of Creation " together. 

 This is a serious matter. Without rushing at once to the 

 conclusion that we can in such cases adopt the idea conveyed 

 in the famous epitaph — 



Lie heavy on him, Earth : for he 

 Laid many a heavy load on thee, 



or insisting with the Greek philosopher of old that a big 

 book is a big evil, we may at least ask whether the import- 

 ance of the contents, in this case, corresponds with the 

 weight of the book. It may be temper resulting from 

 wrist-weariness, or it may not, but we are moved to say 

 that the number of pages in Professor Langley's book 

 is surprisingly small compared with the weight ; the quan- 

 titj' of matter surprisingly small compared with the number 

 of pages ; the amount of astronomical information amazingh' 

 small compared with the quantity of matter ; the proportion 



" The New Astronomy. 

 Tlclcnor & Co.) 



By Professor S. P. Langley. (Boston : 



