July i8, 1901] 



NA TURE 



279 



other with a pocket sextant and ice horizon, justify the con- 

 clusion that the terrestrial refraction was so abnormal, that the 

 computation of the latitude necessitated the reversal of the sign 

 of the dip ; but that this state of things was local, and that the 

 observations of another observer only ninety miles away would 

 not be so affected, though the temperature and general condi- 

 tions were in both cases practically the same. (See comparison 

 between the corrections for refraction in the meridian altitudes 

 of Nansen at his Farthest North, and Hansen on board the Frani, 

 April 6, 1895). 



Admitting to the full the truth and justice of the remark of 

 your reviewer in connection with the observations taken during 

 Nansen's sledge expedition, that "the fact that observations 

 were taken at all is the strongest possible evidence that scientific 

 zeal is compatible with the possession of remarkable courage," 

 it must also be admitted that a comparison of these scientific 

 results with those which Nansen obtained from the same times 

 and altitudes proves that scientific zeal and the power of taking 

 observations are also compatible with the inability to compre- 

 hend the very elementary fact that if the results of two or more 

 observations differ widely from each other neither is trustworthy, 

 and that geographical positions and condemnations of the work 

 of such men as Julius Payer and Wyprecht cannot, and ought 

 not, to be based upon them. 



Should any student of practical nautical astronomy go to the 

 trouble of making this comparison, he cannot, I think, fail to 

 perceive at every step that, however painstaking Prof. 

 Geelmuyden and his colleagues have been in their attempt to 

 plot Nansen's route on his celebrated sledge journey, they have 

 been compelled to ignore his own statements and his own 

 workings, and while straining at the scientific gnat they have 

 freely swallowed the practical camel. Dr. Nansen had led us 

 to believe that the scientific results would explain and justify his 

 already published results. It can be easily shown that one or 

 the other is hopelessly wrong. They are totally irreconcilable. 

 If it is for one moment admitted that Nansen had the oppor- 

 tunity and ability to work the common observation for longitude 

 by chronometer, then Prof. Geelmuyden's primary hypothesis is 

 unsound. If it is maintained that that hypothesis is even 

 approximately correct, Nansen's own recorded results become 

 ridiculous. 



Turning from matters of fact to matters of opinion, two 

 statements of great interest to explorers in high latitudes may 

 be noticed. On p. 14 we are informed that one of the com- 

 puters employed with advantage the difference of altitude near 

 the prime vertical to determine the latitude. Now in low lati- 

 tudes, where the change of altitude is rapid, say from 10' to 15' 

 per minute of time, a result within five or ten miles of the 

 truth is perfectly possible. In latitudes from 70° to 85" N., 

 with altnudes changing at most 5' or 6' per minute of time, and 

 affected by refraction abnormal in itself, and varying rapidly 

 according to no well-defined law, the method entirely fails. If 

 a chance observation appears to justify its use, the altitudes 

 must be accidentally or miraculously correct. 



The remark on lunars, p. 22, will strike experienced obser- 

 vers as exceedingly curious. " The results," says Prof. Geel- 

 muyden, "are not satisfactory." 



Table C, p. 44, shows that eight observations were taken at 

 various times, and from them Greenwich Mean Time was deter- 

 mined with errors varying from 18 seconds to 2 minutes. On 

 ihe assumption that the explorers might have been dependent 

 on them, their positions would have been affected with a 

 maximum error of 30' of longitude, or about four geographical 

 miles. Let future explorers note this. It may safely be affirmed 

 that these results will seldom lie surpassed by men taking lunars 

 under Arctic conditions. It may with equal truth be said that 

 for the purposes of such explorers greater accuracy is unneces- 

 sary ; and the submission to a practical test of Prof. Geel- 

 muyden's opinion, that better results can be obtained by deducing 

 the moon's right ascension from the difi'erence of azimuth of the 

 moon and a star, will he a task not unworthy of the scientific 

 expert accompanying the Discovery. E. Plumstead. 



"First on the Antarctic Continent." 



Some rather venomous criticism of my book, " First on the 

 Antarctic Continent," has appeared in one or two periodicals. 

 Had my book been intended to be what it is not — a scientific 

 report upon our work in the south — the venom would to some 

 ex tent be justified. There are, however, other circumstances 



NO. 1655, VOL. 64] 



which prevented me from producing at the time a larger and 

 more representative account of our work in the south. Pre- 

 liminarily may I state that the observations have been sub- 

 mitted to the Council of the Royal Society, who have accepted 

 them, and the Society is in due time going to publish a volume 

 on the results.' This speaks for itself of the efficiency of the 

 staff I had chosen. The Natural History Museum of South 

 Kensington has received the bulk of the collections and I under- 

 stand that the report upon them is nearly finished, and the 

 book, written by specialists of the Museum, will probably appear 

 within a very short time. C. E. Borchgrevink. 



(Commander, British Antarctic 

 Expedition, iSgS-igoo). 

 Douglas Lodge, Bromley, Kent, July 5. 



The Settlement of Solid Matter in Fresh and Salt 

 Water. 



In a letter under the above heading in your issue of June 20, 

 Mr. W. H. Wheeler discusses the effect of dissolved salt in 

 promoting the subsidence of alluvial matter in water. He takes 

 exception to the conclusion of Mr. Slidell that the mixture of 

 sea water with river water exercises a preponderating influence 

 on the formation of deltas. The question at issue is not one 

 that can be settled simply by a consideration of the specific 

 gravity and viscosity of the solutions employed, and Mr. 

 Wheeler has made it the subject of experimental investigation. 

 There can be little doubt that it is only in the case of very 

 finely divided solid matter in suspension that the addition of 

 salt solution causes increased precipitation, and so far his 

 results can scarcely be called into question. They are confirmed 

 by the investigations on the deposition of sediment by Carl 

 Barus and Bodlknder, to whose papers references are given 

 below. 



The precipitation of such "suspensions" or " pseudo- solu- 

 tions" by the addition of an electrolyte is accompanied by the 

 coagulation or flocculation of the solid matter. Schloising 

 states that clay suspensions pass through a filter paper, but can 

 easily be filtered if coagulated by a salt solution. If, however, 

 the clay is washed free from salt, it can enter into suspension 

 again in pure water and be precipitated afresh. These two 

 operations can be performed in succession several times 

 without apparent modification in the results. Picton and 

 Linder found that the coagulum produced by the precipitation 

 of a pseudo-solution of arsenic sulphide contained traces 

 of the metallic ion, which could not be removed by washing. 



The mud or ooze examined by Mr. Wheeler seems to have 

 consisted entirely of matter which had already undergone pre- 

 cipitation, but it does not appear from his letter that any 

 precautions were taken to remove traces of the metallic salts, 

 so that it remains doubtful whether the sample really formed 

 a suspension in the pure water. More satisfactory experiments 

 could perhaps be made by collecting samples of tutbid water 

 from a river in flood and then adding sea water or a solution of 

 salt. 



I had occasion soine time ago to consult the somewhat exten- 

 sive literature dealing with the suspension of solid matter in a 

 fluid and the allied one of colloidal solutions, and the following 

 list of papers, though doubtless far from complete, may be of 

 use to some readers of Nature : — 



Skey, Cheui. News, xvii. p. 160; Waldie, Chem. N'.-ms, July 

 24, ifqw Journ. As. Soc. Bengal, 1873 ; Th. Scheerer, t'og}^. 

 Ann., Ixxxii. p. 419, 1851, einige Beobachtungen Uber das 

 absetzen auf geschwemmter pulverformiger Korper in Flussig- 

 keiten ; Hunt, Proc. Bosl. Soc. Nat. Hist., pp. 302-4, 1S74 ; 

 Slidell, Report of Messrs. Humphreys and .\bbott on the 

 physics and hydraulics of the Mississippi, App. .K, p. 11, 1S61 ; 

 Ch. Schloesing, Compt. rend., Ixx. p. 1345, 1870, sur la precipi- 

 tation des limons par des solutions salines tres-etendues ; 

 David Robertson, Glasgow Geol. .Soc. Trans., iv. pp. 257-9, 

 1874; W. Durham, Chem. News, xxx. p. 57, 1874: Chem. 

 News, xxxvii. pp. 47-S, 1878 ; Proc. Roy. Phys. Soc. Edin., iv. 

 pp. 46-50, 1874; W. H. Brewer, Proc. Nat. .\cad. Sci., 1883 ; 

 Amer. Journ. (3), xxix., p. I, 1SS5 ; C. R. Stuntz, Cincinnati 

 Soc. Nat. Hist., Feb. 1886 ; E. W. Hilgard, Amer. Journ. vi., 

 1873, xvii., 1879, Forschungen auf d.Geb.d.Agriculturphysik von 

 E.Wollny, ii. pp. 57-9,441-454, 1S79, ueberdie Flockung kleiner 

 Theilchen; A. Mayer, Forschungen aufd. Geb. d. Agriculturphysik 

 von E.Wollny, ii. pp. 251-273 ; Hallock, Bull, of the U.S. Geol. 

 Survey, xlii. p. 137, 1SS7 ; Carl Barus, Bull, of the U.S. Geol 



