Februarv i6, 1899] 



NA TURE 



367 



These distinctions between antlers and the different 

 types of horns are certainly the clearest and neatest that 

 have come under our notice ; and they naturally lead the 

 author to the conclusion that the Cervidac form one group, 

 and the other three families mentioned a second division 

 of the Pecora. If his views obtain acceptation, they 

 refute the late Prof. Garrod's theory of the near relation- 

 ship of the musk-deer to the Bovidac. 



Whether ot no his pi-edilection for abnormalities will 

 bear any good fruit, the author has evidently devoted 

 much pains-taking labour to the present fasciculus ; and 

 the issue of the remaining parts of the work will be 

 awaited with interest. R. L. 



Recent Advances in As/ronoiiiy. By A. H. Fison, D.Sc. 



Pp. vi -I- 237. (London : Blackie and Son, 1898.) 

 In the course of half a dozen essays the author of this 

 volume of the "Victorian Era Series " has attempted to 

 give an account of a few of the more interesting problems 

 of modern astronomy. While the book is admirably 

 written throughout, the subject-matter is in some respects 

 not sufficiently up to date. For example, in the essay on 

 the " life of a star," which is otherwise exceedingly 

 interesting, there is practically no reference to the 

 spectroscopic evidence bearing on the subject ; and 

 again, in that on the " analysis of starlight," there is no 

 account of the different kinds of stellar spectra and their 

 probable relationship to each other, most of this chapter 

 bemg concerned with motion in the line of sight. 



One of the best essays is that on Mars, which sum- 

 marises what we know of that planet, as well as the 

 various speculations to which such knowledge has led. 



The book is notably free from errors for a first edition ; 

 but we may point out that the discovery of carbon in the 

 sun was not made in iSS", as stated on p. 187, but was 

 announced by another investigator altogether in 187S. 



It is unfortunate that, either for want of time or oppor- 

 tunity, the author has not gained a closer acquaintance 

 with recent spectroscopic investigations. Had he done 

 so, his book would have been much improved. Never- 

 theless, the selected subjects are treated in an able 

 manner, and the book deserves to be widely read. 

 Among the Celestials. By Captain Francis Young- 

 husband, CLE. Pp. 26r. (London : John Murray, 



1S98.) 

 The inspiring volume entitled "The Heart of a Con- 

 tinent," in which Captain Younghusband gave a straight- 

 forward record of ten years' travel in Manchuria, across 

 the Gobi Desert, through the Himalayas, the Pamirs, and 

 Chitral to India, was revie\\ed at length in these columns 

 in 1S96 (vol. liv. p. 130). The present volume has been 

 abridged from the original work, by omitting geo- 

 graphical details which, though of service to geographers 

 and travellers, are not of interest to the general public. 

 The previous book will be published in two parts. 

 The first part, now before us, deals with Captain Young - 

 husband's travels in the Chinese Empire, a chapter on 

 the outlook in Manchuria being added. The second part 

 will describe experiences and impressions obtained 

 ■during travels in the borderland between British and 

 Russian territory in Central Asia. 



There should be many readers for Captain Young- 

 husband's interesting narrative in the form it is now 

 presented. 



A Cotswold Village : or. Country Life and Pursuits in 

 Gloucestershire. By J. Arthur Gibbs. Pp. xvi -t- 431. 

 (London: John Murray, 1S98.) 

 Field naturalists, and all other admirers of natural life 

 and scenes, will read this volume with pleasure. The 

 book is of the gossipy kind, and village characters and 

 •customs figure prominently in it ; but many keen observ- 

 ations are recorded, and the descriptions of pastoral 

 scenes will delight all who love the country. 

 NO. 1529, VOL. 59] 



LETTERS TO THE EDTTOR. 

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

 pressed by his correspondents. Neither can he nm'e'-'ake 

 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.^ 



Production of Magnetisation by Circularly Polarised 

 Light. 



In Nature for January 5, Prof. Fitzgerald points out that a 

 beam of circularly polarised light sent through a substance 

 absorbent in consequence of syntony with the vibration ought 

 to produce magnetisation of the substance. The result of the 

 experiments he has set on foot will be awaited with much 

 interest. 



In the Proceedings of the Royal Society for February 17 of 

 last year Prof. Fitzgerald pointed out also that the Zeeman and 

 Faraday effects are related phenomena. I may mention that 

 in the Phil. Mag. for December 1890, I gave a very slight 

 sketch of experiments I had carried out from time to time 

 during several years previously, with the view of discovering 

 the effect which theory had seemed to me to prove ought to be 

 produced by the passage of circularly polarised light through a 

 medium showing the Faraday effect. I have made many ex- 

 periments of this kind with a bar of Faraday's heavy glass, 

 looking for the production and disappearance of a magnetic 

 field (with the excitation and quenching of the beam) by 

 means of an induction coil wrapped round the bar. Calculation 

 shows that the effect in such a case should be very small — so 

 small as perhaps to be quite inappreciable. The investigation 

 is, however, being resumed with improved apparatus and 

 arrangements which I hope may not be entirely without result. 



Andrkw Gray. 



Magnetic Perturbations of the Spectral Lines. — 

 Further Resolution of the Quartet. 



For some time past I have been in hope that, with the strong 

 magnetic field now at my disposal in the Physical Laboratory of 

 the Royal University of Ireland, I might perhaps be able to 

 effect some further resolution of the spectral lines. For example, 

 in the case of a line which is converted into a triplet (normal 

 type) by a magnetic field of strength 20,000, or thereabouts, it is 

 possible that each constituent of this triplet may become further 

 resolved into a doublet, or a triplet, when the strength of the 

 field is increased to 40,000 or 50,000 C.G.S. units. 



Although I cannot yet affirm that the normal triplet becomes 

 further resolved in very intense fields (but symptoms of a 

 further resolution into doublets are sometimes seen), yet, on the 

 other hand, it has been placed beyond all doubt that the 

 " quartet " form becomes further resolved when the strength of 

 the field is increased. 



The quartet form, it will be remembered, consists of two 

 strong side lines with two .fainter lines between them — the 

 latter pair corresponding to the middle line of the normal 

 triplet. When the strength of the magnetic field is gradually 

 increased, the side lines begin to separate into pairs : and ulti- 

 mately, what was at first a quartet stand forth as a sextet of well- 

 defined sharp lines. We may take it, therefore, that the quartet 

 form has ceased to exist as a distinct type, except for this one 

 peculiarity, viz. that in it the separation of the middle pair is 

 considerably greater than that of the side pairs.' The exact 

 ratio of these separations I have not yet determined with pre- 

 cision, but I hope to give measurements on this and some other 

 matters at an early date. 



It is not to be understood that this further resolution raises 

 any new difficulties in the way of theoretical explanation, for, 

 as I have already pointed out (Phil. A/ag., February 1899), the 

 purely precessional perturbation of the orbit which gives rise to 

 tripling pure and simple is by no means likely to be unaccom- 

 panied by other subsidiary perturbations of more or less intensity, 

 such as oscillations of the plane of the orbit, apsidal motions, 

 and so on, and such perturbations as these explain the existence 

 of types other than the normal triplet. In fact, things appear 

 very much more natural, as well as more interesting, now that 

 we know that the triplet pure and simple is likely to become 

 the exception rather than the rule. Thomas Presto.N". 



Dublin, February 9. 



ntrary, D.j 



\ of eq natty spaced Hi 



