October 1 1, 1906] 



NA TURE 



587 



LOWELL'S OBSERVATIONS OF THE 

 PLANET MARS.' 



T N llio year 1S93 the important volume on .Mars, 



i entitled " La " Planete Mars et ses Conditions 

 il'llabilabilite," was noticed in tliese columns (vol. 

 ^Ivii., P- S=,3)- 'I'his work, the outcome of an immense 

 amount of labour on the part of M. Camille Flam- 

 niarion, brought toy:ether every available observation 

 and piece of information that could be gathered from 

 published and unpublished works. In fact, the 

 history of the observations made on this interesting 

 planet was traced from the time of the earliest 

 record (1636) down to the opposition of 1892. 



Fourteen years have now elapsed, numerous workers 

 have been busy studying his surface markings, and 

 steady progress has "been made in corroborating old 

 and discovering new features. The time seems, 



therefore, ripe for a work supple- 

 mentary to that above named which 



-.hould ' bring together the. mass of 



valuable material which is now scat- 

 tered through many different pamphlets 



and journals. 



Such an undertaking would un- 



(loubtedlv consume much time and 



labour on the part of the compiler, but 



would prove a valuable addition to the 



literature of planetary astronomy. 

 Failing such a work at the present 



lime, we have, however, a volume 



which will not only fill up the gap 



temporarily, but will reduce to a very 



considerable extent the labour of the 



future compiler to whom reference is 



made above. 

 This very handsome and valuable 



publication gives a detailed account of 



I he observations made by Mr. Percival 

 Lowell himself during the oppositions 

 iif 1894, 1896, and 1903; the supple- 

 ment to the volume contains tlie observ- 

 ations of Mr. Douglass, assisted by 

 Mr. Drew, at the opposition of 1898, 



II wing to Mr. Lowell's absence through 

 illness, and of Mr. Lowell and Mr. 

 Douglass at the 1900 opposition. 



In the arrangement of the subject- 

 matter Mr. Lowell follows the classic 

 memoirs of Schiaparelli, considering 

 e.'ich opposition by itself, and adopting 

 a chronological and topographical 

 order for the observations themselves. 

 In this way, during an opposition, the —Lowel 



-torv runs " on in time while making 

 meanwhile the circuit of the planet." 



.\s is well known, Mr. Lowell preserves Schia- 

 p.arelli's nomenclature, which he refers to as an " at 

 iinre appropriate and beautiful scheme." He makes, 

 however, one important change, which is necessitated 

 in the light of advance of our knowledge of the 

 interpretation of the planet's markings. In the place 

 of " Lacus " he adopts the word " Lucus," an alter- 

 ation of a single letter, for markings which were 

 previously considered to represent water are now- 

 looked upon as probably oases of land. It was Mr. 

 \V. H. Pickering's observations and deductions which 

 lirst suggested this inversion of the then general idea 

 of the dark and light shadings, and this knowledge 

 w.is considerably extended by Mr. Lowell's observ- 

 .itions. 



In the observation of details on a planet's surface 



* " Observations of the Planet Mars, during ttie Oppositions of 1894, 

 1S96. 1898, iQoi and 1903, made at Flagstaff, Arizona." By Percival 

 Lowell. (".Annals of ttie Lowell t )bservatory," vol. iii., 1905.) 



it is well to bear in mind that the power of the 

 telescope is of less im[X)rtance than steadiness and 

 clearness of the air .ind keenness of the observer's 

 vision. In fact, Schiaparelli 's observations of the 

 canals made with his 6-inch telescope were not 

 corroborated at once by observers who were armed 

 with very much more powerful instruments. 



That keen-eyed observer Dawes was accustomed to 

 cut down the aperture of his telescope according to 

 the kind of night experienced. TTius he termed his 

 observing nights 6-inch night, 4-inch night, &c., 

 according to the " seeing." 



In considering Mr. Lowell's observations of Mars, 

 the reader must bear in mind that, unlike most astro- 

 nomers w^ho make their observations from where the 

 observatory is permanently situated, Mr. Lowell 

 investigated the " seeing " conditions of a great 



K go 



s drawing of Mars at longitude 90" at the opposition of 1903, showing Solis 

 Lacus near the top. 



number of regions in order to choose the most 

 efificient spot for the observation of planetary details, 

 and hence the position for his observatory. The 

 steadiness of the air at Arizona thus allowed him to 

 use larger apertures efficiently, and, coupled with 

 his keen sight and expertness in this kind of observ- 

 ation, his observations are of the first importance. 

 He, like Dawes, found that the aperture of the tele- 

 scope had to be suited to the night. Thus of the 

 opposition of tgoo-i, using a 24-inch refractor, he 

 writes (p. loi) : — 



" Observations were made with the 24-inch objective 

 of the observatory and usually with the full aperture 

 of the objective. On occasions, however, this was 

 capped down to an aperture of 12 inches; an optical 

 device which usuallv improved the seeing ; - . . but 

 because bv so doing the harmful effects of the air 

 currents were reduced. For the same reason at times 

 even the 6-inch could be serviceablv used." 



NO. 1928, VOL. 74] 



