278 



NA TURE 



[July i8, 1901 



of these old valleys were revived, bjl in other ca^es the 

 streams followed new courses. The story of all these 

 changes is clearly told by Mr. Reed, and although there 

 is room for difiference of opinion in matters of detail, the 

 main results are based on fact ; and the essay may be 

 profitably studied by those interested in the origin of our 

 scenery. 



Fergussoris Sut-veyins; Circle and Percentage Tables. By 

 J. C. Fergusson, M.Inst.C.E. Pp.84. (Published by 

 the Author, 1901.) 

 This is an account of a device intended to replace the 

 dial or circles in magnetic compasses and surveying 

 instruments, with numerous illustrations of its application 

 for the purposes of engineers, surveyors, naval and mili- 

 tary officers and travellers. Half of the circle is divided 

 into octants, and the graduation of each octant is effected 

 by dividing its tangent, which is equal to the radius, into 

 100 equal parts and then drawing lines from these 

 divisions to the centre of the circle. The divisions on 

 the octant thus always subtend equal spaces on an offset 

 laid out at right angles to the quadrantal radius. The 

 spaces on the octant divided in this manner correspond 

 to a hundredth part of the radius, and the angles being 

 read in percentage divisions, trigonometrical formuUe 

 are replaced by simple arithmetic. A considerable 

 simplification of several practical problems is suggested 

 by the examples given, but the advantages of the method 

 can scarcely be judged without actual experience. It is 

 stated, however, that many distinguished engineers and 

 surveyors have expressed complimentary opinions as to 

 its merits. Messrs. T. Cooke and Sons are the manu- 

 facturers of the new circle, which can be adapted to old 

 or new instruments. 



Ho7v to Knoiu the Indian Ducks. By F. Finn. Pp. 

 iv-l-ioi. (Calcutta: Thacker, Spink and Co., 1901.) 



If the right to include under the name of " ducks " both 

 geese and swans be conceded to the author (and we have 

 some doubt whether it should be), we have nothing but 

 commendation for this excellent little volume. Years 

 ago, when duck-shooting on the Ganges, we have a 

 vivid recollection of our own regret at being unable to 

 identify all the various representatives of the duck tribe 

 included in our "bag," and we have little doubt that this 

 regret has often been shared by other sportsmen. For 

 the future, however, there should be no difficulty what- 

 ever in determining the species of any member of the 

 tribe which may fall to the gun of the sportsman in 

 India, as Mr. Fmn's volume is small enough to be carried 

 in the pocket without inconvenience, while the lowness 

 of its price brings it within reach of every one. Need- 

 less to say, as the author is an accomplished ornithologist 

 who has devoted special attention to the Indian .'Vnatidre, 

 the descriptions are all that can be desired from a 

 scientific point of view, while the simple language in 

 which they are written, and the useful " keys " for the 

 identification of species, render the volume admirably 

 adapted to the needs of sportsmen. 



It is for this class, indeed, that the work is primarily 

 intended, as the author tells us in his preface ; and the 

 fact that the substance of the text has already appeared 

 in the form of a series of articles in the columns of the 

 Asian newspaper bears testiinonyto its favourable recep- 

 tion by Anglo-Indian sportsmen. 



On more than one occasion we have directed attention 

 in these columns to the confusion caused by the diverse 

 systems of nomenclature followed by ornithological 

 writers. In the present instance we are glad to see that 

 the author endeavours to promote uniformity in this 

 respect by following the classification and nomenclature 

 adopted by Mr. W. T. Blanford in the " P'auna of 

 British India." R. L. 



NO. 1655, VOL. 64] 



LETTERS TO THE EDITOR. 



[ The Editor docs not liotd liiinself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return^ or to correspond with the writers of, rejecei 

 ■.nantiscripts intended for this or any other part of NATURE. 

 No notice is taken of anonymous communications.'^ 



On the Determination of Positions in Polar 

 Exploration. 



Having in view the importance of this subject in connection 

 with the forthcoming Antarctic expedition, a brief comment on 

 the results obtained m high latitudes, with which we have been 

 favoured during the last few months, may not be out of place. 

 The publication of the scientific results of the Nansen expedition 

 is now before us, and these, together with a few which (with- 

 out further explanation perhaps) scarcely merit the employment 

 of this adjective, and which are to be found in the pages of Mr. 

 Borchgrevink's account of the Southern Cross expedition, 

 afford food for reflection, but whether they could be more satis- 

 factorily dealt with by a professional man of science or a 

 professional humorist may be open to question. The first have re- 

 sulted in a series of deductions and suggestions which will strike 

 thoughtful men as being eminently unpractical, and the latter 

 is responsible for considerable confusion of mind in regard to 

 the geographical positions of the most important points to 

 which the expedition just about to start is instructed to 

 proceed. 



These being for the moment the more important, may be 

 dealt with first. It has already been pointed out by Nature 

 that the recorded observations of the Borchgrevink expedition 

 are extremely unsatisfactory, owing, possibly, to the work of a 

 copyist ignorant of nautical calculations, but besides being im- 

 properly copied they are improperly computed. One, owing 

 to the use of the secant of an erroneous latitude, is made to 

 produce a longitude 22' in error. Another computes the 

 declination with a correction for longitude instead of for the 

 Greenwich date. A third professes to find the chronometer 

 error to a couple of seconds by a lunar eclipse (a feat which, if 

 true, is miraculous) ; and a fourth produces a longitude of the 

 harbour under the great ice barrier from which Mr. Borchgre- 

 vink effected his landing which is said by the navigating 

 officer to be 164° 32' W., by the commander 164° 10' W., and 

 by the president of the I'loyal Geographical Society 162° 30' \V. 



The position of Cape Adare, again, is of the very first im- 

 portance. Ross placed it in 71° 18' S. ; Mr. Borchgrevink 

 finds this latitude correct, but places it 36' further to the East ; 

 while Sir C. Markham, if we may judge by the Geographical 

 Journal for July, has apparently been informed that it lies in 

 lat. 71° 30' S. 



Much satisfaction has been expressed at the supposed verifica- 

 tion of the position of two groups of islands (the Balleney 

 groups), but much astonishment has also been expressed by 

 thinking men that the Geographical Society can attach the 

 faintest importance to the determination either of their number 

 or their position by officers who, in discussing the subject, con- 

 tradict each other flatly both as to the date, the appearance and 

 the distance of the land at the time of the discovery ; to say 

 nothing of the suggestion that at distances ranging from 90 to 

 40 miles abundance of detail, including crevasses, and the shore 

 line were plainly visible. 



Turning to the sciendfic results of the Nansen expedition, 

 and having in view the remark of your reviewer (Nature, June 

 13), that the volume is to be welcomed as exceedingly oppor- 

 tune in view of the approashing Antarctic expedition, I should 

 like to call the attention of the scientific stafl" to certain informa- 

 tion which they may find it interesting to put to a practical test. 

 It is here suggested : — 



(1) That the value of refraction can be estimated from astro- 

 nomical observations taken during a drift, when the latitude by 

 which the altitudes are computed depends upon the unknown 

 refraction and the refraction upon the unknown latitude. (See 

 table of refractions). 



(2) That the altitudes necessary for the computation of a lunar 

 distance can be calculated by a man having no knowledge of 

 his Greenwich time and being uncertain of his longitude to the 

 extent of from 15 to 25 degrees. (See Nansen's lunar, taken 

 August 10, 1895). 



(3) That the discrepancy between two sets of altitudes taken, 

 the one with a glass horizon labouring under suspicion and the 



