Oct. 3, 1872] 



NATURE 



45, 



method is given for the separation of lanthanum and 

 didymium, but in the present there are no less than four 

 distinct methods given. On the subject- of the alkaloids, 

 we notice three new articles on digitaline, picrotoxinc, and 

 atropia, which in the previous edition are not noticed. In 

 the portion which treats of the acids, and in Part II. 

 " On the Course of Analysis," there does not appear to be 

 much alteration ; but we must not omit to mention that 

 the index to this edition is far more complete, and in 

 every way better than in the previous editions. The 

 general plan of the work is too well known to need any 

 detailed account, and the number of editions through 

 which it has passed is a sufiicient guarantee of its useful- 

 ness and trustworthiness. A few new illustrations have 

 been introduced, and a new table of spectra, but in the 

 general style and plan of the book there has been no al- 

 teration. For our own part, although we have a great 

 admiration for Fresenius's book, more especially as a work 

 of reference, we scarcely think that his system is perfect 

 for educational purposes, and perhaps not so good as 

 those of some others, such as Valentin's or Galloway's ; 

 no doubt a student working conscientiously through 

 the work under review will be able to make good and 

 correct analyses, but we doubt whether he will learn 

 much beyond the mere analytical details, for in this 

 book there seems little room for the student to use his 

 powers of originality, and nothing to stimulate him to 

 reason, from his accumulation of facts, to general princi- 

 ples. There appears about the book almost too much of 

 the system of telling this and showing that, for the book 

 to be perfect as an educational agent, and we fancy that 

 better results in this direction may be obtained from 

 works which give more opportunity and encouragement 

 for original and individual reasoning ; and this we believe 

 is the case in the two other works we have mentioned, 

 as they tend to exercise and strengthen the student's origi- 

 nality, and will at the same time give him as full and 

 complete a knowledge of qualitative analysis as lie would 

 obtain from Fresenius's book. 



OUR BOOK SHELF 



Vcrhandhiagen des naturhisiorischen Vcreines dcr prciis- 

 sischen Rlicinlandc tind IVi-stphalcns. 28" Jahrgang. 

 1"= u. 2"= Halfte. (Bonn, 187 1.) 



The volume of these Transactions for 1S71 opens with 

 biographical memoirs of Wirtgen and Haidinger. S. 

 .Simonowitsch contributes a paper on the Eryozoa of the 

 Greensand of Essen, illustrated by four lithographic plates, 

 which is introduced by a critical account of the anatomy 

 and systematic position of the Bryozoa. From Prof. 

 Forster we have a Review of the Genera and Species of 

 the Family of PlectiscoidecU. F. G. Herrenkohl follows 

 with a list of the Phanerogams and Vascular Cryptogams 

 of Cleve and the neighbourhood. R. IJluhme gives a 

 scries of analyses of the water of different wells in the 

 vicinity of Bonn, compared with that of the Rhine. In 

 addition to these papers printed at length, a large number 

 of other subjects connected with medical and natural 

 science are treated in the Reports of the Proceedings of 

 the Lower Rhine Society for Natural History and Medi- 

 cine. Among these we may refer especially to a valuable 

 paper by Dr. IJrandis on the climatic conditions which 

 principally affect the growth of forests in the British East 

 Indies. The Indian climate is characterised by its long 

 period of uninterrupted drought ; and where the rainy 



season falls in spring or autumn, the summer heat is ex- 

 cessive. Where, however, the rainy season i'alls in the 

 summer, as is the case in Burmah, Bengal, and a portion 

 of Central India, the climate presents the peculiarity that 

 the hottest period is in the spring, from March till May 

 and the commencement of the monsoon, and again in the 

 autumn, Calcutta having again a compai'atively cold 

 winter. The great obstacle to the growth of forests is the 

 prevalence of fires towards the close of the dry season, 

 which do incalculable damage every year ; but of late 

 years something has been done to limit their ravages. 

 The growth of tree vegetation is extraordinarily rapid iii 

 India when young, but the forests do not eventually attain 

 such luxuriance as in Ceylon, Brazil, and some extra- 

 tropical countries. 



LETTERS TO THE EDITOR 



[ The Editor doc's no! hold himself responsible for opinions expressed 

 by his correspondents. No notice is taken of anonymous 

 communications. ] 



Oceanic Circulation 



The letters of Prof. Everett and Mr. Wallace (Nature, 

 Aug. 22) establish one point which must go a good way towards 

 the settlement of the disputed question of the cause of oceanic 

 circulation, viz., that in order to maintain the bare mechanical 

 possibility of the gravitation theory, it is necessary to assume 

 tliat water is so neariy quite devoid of molecular resistance to 

 motion that, were it not for the impediments offered by conti- 

 nents, water flowing from a low to a comparatively high latitude 

 would be revolving eastwards with the velocity of an arrow. 

 In the soutliern hemisphere, where continents are "few and far 

 between," and where a comparatively open channel exists through 

 which the waters may circulate round tlie globe at any velocity 

 without nnich impediment, this rapid general eastward motion of 

 the ocean ought to be developed to a large extent. But the 

 fact remains that no such motion has ever been observed. Dr. 

 Carpenter says :— " It is well known to navigators that tliere is 

 a perceptible ' set ' ot warm surface water in all the southern 

 oceans towards the Antarctic Pole ; this ' set ' being so decided 

 in one part of the Southern Indian Ocean as to b/compared by 

 Capt. JMaury to the Gulf Stream of the North Atlantic" (Nature, 

 March 24, iSyo). This general motion of the water in the 

 ^outhern hemisphere Dr. Carpenter adduces as strong evidence 

 in favour of his theory. Put why is not the " set " as much to ' 

 the east as to the south ? If the presence of the Antarctic con- 

 tinent does not hinder the motion of the water polewards, why 

 should the presence of the continents of Australia or the southern 

 portion of South America hinder the motion of the water east- 

 ward, seeing that rotation performs about 1,500 times more work 

 in deflecting the water eastward than the difference of specific 

 gravity performs in impelling the water southward ? The very fact 

 that the water does not turn to the east but moves straight to- 

 wards the Antarctic continent, shows that the waters must be 

 iinpelled by a force immensely greater than that derived from 

 difference of specific gravity, because it must be greater than that 

 derived from rotation, or else the "set" would be as much to 

 the east as to the south. There are, it is true, a few currents in 

 the southern hemisphere with an eastern motion, but these the 

 advocates of the gravitation theory would call " mere surface 

 drifts produced by the winds." .Besides the majority of the 

 currents in that hemisphere move in wrong directions to be ex- 

 plained either Ijy difference of specific gravity or by rotation. 



That the explanation given by Prof Everett and Mr. Wallace 

 does not even touch the difficulty which besets the gravitation 

 theory, far less removes U, will, I trust, be further evident from 

 the following considerations, viz., a current in mid-ocean a 

 thousand miles from land, flowing from a low to a higher lati- 

 tude, h.as its eastward motion due to rotation as effectually 

 checked and diminished as though it abutted against a continent. 

 This'retardation cannot be attributed to the presence of continents, 

 for it occurs equally the same whether the land be one thousand, 

 two thousand, or five thousand mdes to the east. It is the re- 

 sistance of the molecules of the water through which the current 

 moves tliat destroys the eastward motion. No matter how slow 

 the current may How polewards, by the time the water reaches, 

 say latitude 60°, each pound has lost at least 9,000 of the 



