April 14, 1892J 



NATURE 



557 



mere " feverish colds " ; yet all such cases would have to 

 be isolated in view of a threatened epidemic. 



The extracts from the various Sanitary Acts appended 

 to these papers form a very convenient work of reference 

 for those interested in the subject, while the counsel's 

 opinion on the powers of sanitary authorities as to in- 

 fluenza leave us very much where we were before. Dr. 

 Sisley has, however, done valuable service in calling 

 public attention to the inadequacy of our existing sani- 

 tary laws as a means of checking the spread of such a 

 disease as influenza, and many will cordially indorse his 

 opinion that " much improvement in this respect is not to 

 be hoped for [until the sanitary service is consoUdated, 

 and becomes one fold under one shepherd — a Minister 

 of Public Health." 



OUR BOOK SHELF. 



Anthropogeographie. Zweiter Theil. "Die Geograph- 

 ische Verbreitung des Menschen." Von Friedrich 

 Ratzel. (Stuttgart: J. Engelhorn, 1891.) 

 The first part of this work was published about nine 

 years ago, and is still highly valued by all who care to 

 study geography and anthropology from strictly scientific 

 points of view. The present volume will also be found 

 worthy of the author's reputation as one of the foremost 

 authorities on all questions relating to the connection 

 between man and the physical conditions by which 

 he is surrounded. In the first part Dr. Ratzel deals i 

 with the habitable part of the globe, tracing the pro- 

 cess by which man has taken possession of it, indi- 

 cating the development of his ideas regarding it, and 

 noting the characteristics of its northern and southern 

 borderlands and of its vacant spaces. The second part 

 he devotes to various aspects of statistics, discussing, 

 among other things, the relations between density of 

 population and degrees of civilization. In the third part j 

 are considered the traces and works of man on the sur- 

 face of the globe — a subject which leads the author to 

 treat of cities and their importance as historical centres, of 

 ruins, roads and other means of communication between 

 communities, and geographical names. The fourth and 

 last part relates mainly to ethnographical questions, in- 

 cluding questions as to the diffusion of ethnographical 

 characteiistics, and the origin of ethnographical affinities. 

 The work is not only full of thought and learning, but has 

 the advantage of being written in a fresh, clear, and 

 vigorous style. 



Within an Hour of London Town: Atnottg Wild Birds 

 and their Haunts. By "A Son of the Marshes." 

 Edited by J. A. Owen. (Edinburgh and London : W. 

 Blackwood and Sons, 1892.) 

 " A Son of the Marshes " is now so well known that 

 any new book by him is sure to find readers and admirers. 

 He does not, of course, make important contributions to 

 science. His writings merely record the impressions 

 produced upon him by various aspects of nature in which 

 he happens to be especially interested. But his im- 

 pressions are so thoroughly true, and are presented in 

 so vivid a style, that they may always be studied with 

 pleasure. Even his talk about very common things has 

 a certain charm, for he observes them accurately, and 

 brings out by skilful touches their relations to other 

 things that are not quite so intimately known. The 

 present volume has all the characteristics of his previous 

 books, and should do a good deal to foster in the mind 

 of " the general reader " a liking for some of the more \ 

 attractive facts and ideas of natural history. 



NO. I 172, VOL. 45 j 



LETTERS TO THE EDITOR. 



\The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.^ 



Exchange of Professorial Duties. 



The proposal of my friend Prof. Anderson Stuart, explained 

 in the subjoined letter, seems to me one which may very 

 probably commend itself to the professors and governing bodies 

 of some of our Universities and University Colleges ; and 1 

 therefore venture to ask for its publication in Nature. By 

 correspondence twelve months in advance, such an exchange as 

 is here suggested could be arranged (with the assent of Senate, 

 Council, or other authority), and would undoubtedly, where 

 practicable, be of very great interest and advantage, not only to 

 the teachers concerned, but also, in no less degree, to their 

 classes. E. Ray Lankester. 



Oxford. 



Shepheards Hotel, Cairo, February 13, 1892. 



Dear Professor Ray Lankester, — In conversations with 

 teachers in Europe during my two visits (1890-91, 1891-92) they 

 have' again and again said how much they would like to visit the 

 colonies for pleasure, health, or the opportunity of study, as the 

 case might be ; but of course they could not, being bound by 

 their duties. On the other hand, the benefit to the colonial 

 teacher of a periodical visit to.the older centres of learning has 

 all along been recognized. 



Soon after my return to Sydney in March 1891, it occurred to 

 me that it would be easy to secure at once a visit of a European 

 teacher to the colonies and of a colonial teacher to Europe by a 

 temporary exchange of duties. Every now and again it happens 

 that a teacher must provide for the duties of his office by a 

 substitute, as is done by the colonial teacher when absent on 

 leave, and by the European teacher most frequently, perhaps, 

 when ill. Why, then, should not two teachers in a subject, 

 who could trust each other, agree to apply for leave of absence, 

 each proposing the other as his substitute for the time specified? 

 I cannot see that any governing body could reasonably object to 

 the proposal, and so the arrangement would be concluded. 



Immediately on my return to Europe in October last I spoke 

 of the matter, and amongst others to yourself ; and since then I 

 have discussed it with many friends, one of whom referred to it 

 approvingly at a recent meeting of the Royal Colonial Institute. 

 The project becomes the more feasible the more one studies the 

 details of carrying it out. Practically one's attention is confined 

 to America and Australasia. A study of the periods of the 

 University terms, and of the steamship time-tables, shows that 

 it is feasible for the latter, which is by far the more distant — 

 about five weeks. 



Of the pleasures of the voyage, and of the advantages to be 

 derived by the residence in the other land, I need not speak, for 

 each may form his own estimate of these; but that "there is 

 something in " the thing I am persuaded, and I should be glad 

 of your help in ascertaining what that something may be. 



I am, dear Professor Ray Lankester, 

 Yours faithfully, 



T. P. Anderson Stuart, 

 Professor of Physiology, University of Sydney. 



Magnetic Storms. 

 Exactly twenty-seven days from the magnetic storm and 

 splendid aurora of February 13-14, which has already been men- 

 tioned in NATURE,there was on March i2another very fine aurora 

 in the United States and Canada, and it also was accompanied by 

 a powerful magnetic storm. This correspondence to the time of 

 a synodic revolution of the sun, to which attention has been 

 called by the writer many times within a few years past, is 

 interesting, showing as it does that the motion of rotation is 

 concerned to an important extent in the recurrence) ofj magnetic 

 storms and their accompanying auroras. The evidence is 

 accumulating constantly showing that solar disturbances have 

 their maximum effect upon terrestrial magnetism when at the 

 eastern limb and at or near the latitude of the plane of the 

 earth's orbit. If the great sun-spot to which the aurora of 



