i6o 



NATURE 



IDec. 13, 1883 



the appearance in 1871 could in no way be included under the 

 general formula, without admitting thai the resisting medium 

 had ceased to operate, or that the comet during the revolution 

 immediately preceding had undergone a sudden retardation 

 through the intervention of some unknown force. Following up 

 at first the latter hypothesis, he was able to assign approximately 

 the time when such perturbation must have taken effect, and 

 found that at this time the comet was traversing the region of 

 the small planets between Mars and Jupiter. This circumstance 

 led Asten to conjecture that the attraction of one of these bodies, 

 which the comet had encountered, might have occasioned the 

 retardation. 



A similar retardation was indicated again by the last appear- 

 ance of the comet in 1881, and, following a similar method, 

 Dr. Backlund was able to fix the time and the approximate 

 place, which was again found to be in the midst of the zone of 

 small planets. Thus, as M. Otto Struve remarks in his report 

 upon Dr. Backlund's memoir, there was reason to think that we 

 were upon the traces of a very interesting discovery, which 

 added much to the interest attaching to his new researches on 

 the last four appearances of the comet, as a complement to the 

 investigations of Asten for the period 1819-1868. This addi- 

 tional work has not, however, led to a confirmation of the 

 above-named hypothesis, but has replaced it by results of a more 

 piositive character and of greater scientific importance. 



Dr. Backlund had found, on following rigorously the rules of 

 calculation adopted by his jiredecessor, that the last four appear- 

 ances, and particularly those of 1871 and 1881, could not be 

 represented without admitting that the acceleration had dimin- 

 ished considerably, and had even disappeared for the last two 

 returns. But on a closer examination it was discovered that a 

 strange error had entered into the combination of the appear- 

 ance of 1868 with the two preceding ones ; in one of these 

 revolutions where the observations made after perihelion w ere 

 combined with those made before the succeeding one, Asten, 

 though he supposed he had taken into account the resistance, 

 had in fact not done so. This being rectified, the errors of 

 1871 and iSSi, which amounted to many minutes, were de- 

 stroyed in great measure, and the discordances reduced to 

 tolerable though still unsatisfactorily large quantities. After a 

 revision of the formulae employed, Dr. Backlund succeeded in 

 reducing the probable error remaining in each co-ordinate of a 

 normal position to 4"'i. The introduction of the mass of 

 Jupiter, according to the determination of Bessel-Schur, further 

 reduced this probable error to 2"'8, assigning for the accelera- 

 tion during the period in question o"-o54 for each entire revolu- 

 tion, and M. Struve considers that Di-. BacKlund's researches 

 have thus put us in possession of a theory of the comet for its 

 later returns which leaves little or nothing to be desired. 



It has been mentioned that for the period 1S19-186S the 

 probable error in the normal positions given by Asten anrounled 

 to 9"-o. Partly, perhaps, the larger error is attributable to the 

 inferiority of the instrumenal means available in the first half of 

 the century, but probably in a gr'eater degree to imperfections 

 detected in the theory adopted for this earlier period, upon which 

 M. Struve's report enters mto some detail. For this reason Dr. 

 Backlund has charged himself h ith the constr-uction of a new 

 theory for the interval 1819-1S68, in which he will be much 

 assisted by the earlier work of Asten, described as having been 

 left in admirable order, and thus admitting of being followed 

 and verified at every step. 



While awaiting the results of these further iuvestigations, M. 

 Struve draws attention to a very singular fact, which will not be 

 affected by them. He remarks there is no reason to doubt that 

 the acceleration has much diminihed in the interval between the 

 mean epochs of the two periods referred to above. He asks : 

 Is it that the volume of the comet has diminished in the 

 interval ? The observations afford no trace of such diminution. 

 Or again, — has the matter of which the comet is composed been 

 increased ? On this we can say nothing. There i-, further, 

 the supposition that the so called resisting medium has altered 

 in density, or again, that the acceleration attributed to the 

 effect of a resisting medium is produced by forces of a totally 

 different nature. 



All this for the moment must remain enigmatical, but the fact 

 is established that the acceleration has diminished ; we cannot say 

 whether this diminution has been produced instantaneously or 

 gradually ; it is a point upon which the new researches under- 

 taken by Dr. Backlund may enlighten us. 



Encke's comet returns to perihelion in March, 1885. 



GEOGRAPHICAL NOTES 



The eleventh number, 1883, of Petermann's Giographische 

 Mitthcilttugni opens with a minute account of the archipelago 

 of Chiloe, by Dr. C. Martin, who in former numbers of the 

 Mitt/intinigeit, in the /\ifis/a cientifica de Chile, and in other publi- 

 cations, has already communicated important information on this 

 part of the earth's surface. The present contribution has special re- 

 ference to vol. viii., recently published at Santiago, oi\.\\e. Anuario 

 de la Marina de C/tile. The ne.xt article gives an interesting 

 sketch of the progress of the knowledge of Kafiristan by Eui-opeans 

 from 1S29, when it first became known to Elphinstone, down to 

 the present year, when Mr. McNair, the Indian Government 

 surveyor, penetrated as far as the Dorah Pass ; and an account 

 of the present state of the inhabitants ethnographically, etho- 

 logically, socially, morally, and religiously, according to the 

 reports of the Rev. Mr. Hughes and other recent visitors. The 

 third article traces the route of the Russian Embassy of 1878-79 

 through Afghanistan and the Khanate of Bukhara, following the 

 descriptions of Dr. J. Jaworski, member of the Russian Geographi- 

 cal Society, who as physician accompanied the Embassy, and has 

 recently published an account of the expedition in two thick octavo 

 volumes in Russian. In a long paper illustrated by a map by 

 Bruno Hassenstein, which also embraces Dr. Junker's expedition 

 through those parts, Dr. Emin-Bey prosecutes his travels to the 

 west of the Bahr-el-Jebel in October and November of last 

 year. Starting from Bedden, on the White Nile, on October 9, he 

 penetrated south-westwards a- far as Janda, the extreme southern 

 post in the Kakuak country, whence he proceeded north-west- 

 wards through the Fadjelu Land, the station Kabajendi, the 

 region of the Makraka and of the Abuka, .as far as the station 

 of Gosa. From this point Dr. Emin-Bey turned south-east- 

 wards through the Abukaja country, and the Makraka-Ssgaire 

 stations, and on Noveirber 26 arrived at the station of Wandi. 

 The Makraka are described as a people dowered, both men and 

 women, with a remarkable profusion of hair, which by means 

 of fat, the sap of trees, &c., they sludiDitsly arrange in plaits, 

 pigtails, &c., producing very surpriiing effects. The name 

 Makraka, though now universally applied to the people of that 

 region, was, it appears, not the original name, but, signifying 

 cannibals, was at first u^ed by the natives to designate a body or 

 invadei-s of the Iddo race from the south. Dr. K. Zopprit?, 

 in the next following article, discusses Dr. Emin-Bey 's measure- 

 ments of heights and atmospherical pressure at Lado. 



We have also received the Mittheihingen of the Geographic.Tl 

 Society in Ilambui-g for 1S80-81. It contains a very copious 

 account of the Island of Lhios (or Scio) geographically, geo- 

 logically, ethnologically, and commercially ; a lecture on the 

 cola-nut, dehvered before the Geographical Society of Hamburg 

 on January 5 of last year, and an instructive description of the 

 " sacred " Japanese town of Kioto. Next follows a very care 

 ful and comprehensive account in 250 pages, by Dr. H. Siegler- 

 scbmidt, of the results of the North Polar expeditions of this 

 century. After summing up our knowledge of the North Polar 

 regions in the year 1S18, the review traces the history of North 

 Polar investigation since that date, taking stock, in particular, 

 of our knowledge of East Greenland, Spitzbergen, the Siberian 

 glacial sea, and other hyperborean tracts. Lastly, it draws up the 

 total results down to the present date in respect of hydrography, 

 meteorology, magnetism, astronomy, &c. In the next article 

 Herr E. R. Flegel gives the first of a series of sketches intended 

 to comprise (l) the mangrove swamps of the delta of the Niger ; 

 (2) the mountains of Cameroon ; and (3) the banks of the lower 

 Niger. In this first sketch we are introduced to the long anil 

 narrow sandy strip of land rising but little above the level of the 

 sea, and running parallel with the coast of the Bight of Benin. 



The I'eyhandlungcn of the Berlin Geographical Society, 

 Bandx., No. 7, contains a very copious article on Wisconsin: 

 and the Zeitschrift of the same society, No. 105, gives the con- 

 clusion of Dr. Kichthofen's account of his travels in China, as 

 also, among other valuable papers, a contribution to the ethno- 

 graphy of the extreme nonh-ea-t of Asia, I y Herr G. Gerland. 



We have further received the Bulletin de la Society de Geographie 

 for the second and third quarters of this year. An article by M. 

 Grandidier briefly describes the | rovince of Imerina, the central, 

 as also the most populous and important, province of Madagascar. 

 The province is mountainous, traversed by numerous water- 

 courses, entii'ely bare of tree or shrub, or often even of cultivated 

 plant, scarcely inhabited in the hilly grour.ds, but thickly peopled 



