43^ 



NA TURE 



[March 9. 1905 



The text amounts to littlo more than a description 

 of the plates and is too scrappv to give a connected 

 view of the subject. The boolc, however, is well 

 produced, and will be valued for its excellent star 

 maps and examples of celestial portraiture. 



Denkmiiler mitlelaUerUcher Mctcorologic. So. 15 

 (Schlussheft). Neudrucke von Schriften und Karten 

 iiber Meteorolosjie und Erdmagnetisnuw lieraus- 

 ijegcben von Prof. Dr. O. Hollmann. Pp. lviii + 

 ibg. • (Berlin: .\sher and Co., 1904.) 

 This is the final volume of a valuable series of publi- 

 cations which we owe to the energ:y of Prof. Hell- 

 mann. In them we have had brought before us the 

 more interesting abstracts and reprints of early works 

 dealing with mctcorologv and terrestrial magnetism. 

 Prof. Hellmann has thus made available to those 

 interested in those subjects, the records of ancient 

 times, which to many would have remained unread 

 and possibly unknown. 



In the present volume, which deals more especially 

 with meteorologv, we have presented to us a set of 

 twentv-six sep.nrate parts ranging from the seventh 

 to the fourteenth century. Many others have been 

 taken from printed works, but some of them, as we 

 are told in the preface, are here published for the 

 first time. 



Further, many of these old texts have here been 

 translated into German so that those who are not 

 familiar with old Saxon, old English, old Norwegian, 

 or Arabic will still be able to gain a good insight 

 into the ideas of the Middle .\ges. 



In the introduction to this volume Prof. Ihllmaiin 

 gives a brief sketch of the character of meteorology 

 at these periods, and adds a short and interesting 

 summary of biographical facts relating to the writers 

 of the texts to which reference is here made. An 

 .ippendix contains additions and corrections to the 

 earlier numbers. 



For the labour involved in bringing together and 

 preparing this collection of old texts a large debt of 

 gratitude is due to Prof. Hellmann, and it is hoped 

 that from time to time, when further ancient writings 

 arc brought to light, he will render them in like 

 manner so conveniently available. 



The Birds of Calcutta. Bv 1". Finn. Second edition. 



Pp. vi+136. (Calcutta: Thacker, Spink, and Co; 



London : Thacker and Co., 1904.) 

 The fact of a work reaching a second edition may 

 generally be taken as an indication that it has re- 

 ceived the seal of public approval, and that it accord- 

 ingly needs no commendation from us. In the present 

 instance, a ready reception would seem to be assured 

 to the new edition, since many additions and im- 

 provements have been made. The most important 

 addition is undoubtedly the series of life-like cuts 

 of Indian birds, which adds very largely to the 

 interest of the little volume; but it is also satisfactory 

 to find that the arrangement and nomenclature have 

 been revised so as to bring the work into harniony 

 with the volumes on birds in the " Fauna of British 

 India," to which it may serve in some degree as an 

 introduction. Mr. Finn has a vivacious, if some- 

 times flippant, style, which removes his works from 

 the " dry-as-dust " category; but in some cases, 

 as in the application of the term " disreputable " to 

 the babbler, we venture to think some ol his epithets 

 might be better selected. To a former resident the 

 omission of the adjutant stork from the list of Calcutta 

 birds seems strange, but it appears that for many 

 years these weird birds have ceased to visit the city 

 of palaces. R- !'• 



NO 1S45, VOL. 7 1] 



Toiling liroinidc Prints. " Photography " Bookshell 

 Series, No. i6. By R. K. Blake Smith. Pp 

 XV+104. (London: UilTe and .Sons, Ltd., 1904. 

 Price IS. net. 

 Instead of producing a black and white bromide 

 print it is often desirable to change the normal torn 

 to suit the subject jihotographed. lliere are many 

 methods by which this change of tints can be ob- 

 laiiud, and these pages are devoted to describing the 

 \arious processes that are available. The material on 

 w hich this book is based first appeared in a series of 

 articles in Plinloi;ral^li\'. but in the present handy 

 form it will be found more convenient for workers. 

 The author gives a good detailed account of each 

 case, and discusses the probable effect of the dilTerent 

 processes on the permanence of the fini--ln'd picture. 

 Workers with bromide papers will find this book of 

 considerable service. J 



LETTERS TO THE EDITOR. 



[The Editor does not bold himself responsible for opinions 

 expressed 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 fallen of anonymous conintunications.] 



Charge on the a Particles of Polonium and Radium. 



\\ ITU reference to the interesting letter on this subject by 

 Prof. Rutherford in last week's Nature, I should like to 

 point out that in my paper " On the positive electrification 

 ol o rays and the emission of slowly movinj^ kathode rays 

 by indio-actiye substances " {,Proc. Camb. Phil. Soc, xiii., 

 p. 40) I have described oxperimenls which demonstrate 

 the communication ol a positive charge of electricity to 

 bodies struck by a rays from polonium or radium. I 

 luul considerable dilViculty in disentangling this positive 

 charge from the copious streams of slowly moving 

 negatively electriticd corpuscles which I found were 

 given out by these substances, and the experiments 

 in wliich 1 finally succeeded in doing tliis were not 

 completed until a few days after the reading of the paper on 

 November 14, and are not referred to in the abstract quoted 

 by Prof. Rutherford. A description of them will be found in 

 the paper which has lately been published. I may take this 

 opportunity of saying that I have recently found that 

 uranium also gives out slowly moving corpuscles, so that 

 this effect seems a general property of radio-active sub- 

 stances. The velocity of these corpuscles is very small com- 

 pared with that of the /3 rays, and is more nearly of the 

 order of the velocity of the corpuscles emitted by metals 

 when exposed to light. J. J. Thomson. 



Cavendish Laboratory, Cambridge, March 4. 



.\ conversation 1 had with Prof. Bragg, of the Adelaide 

 University, in passing through Adelaide last summer 

 suggested some thoughts in regard to the nature of the 

 a rays which may be of interest in view of Prof. Rutherford's 

 letter in last week's Nature. Prof. Rutherford announces 

 that he has at last succeeded in detecting the positive charge 

 carried bv the o rays of radium by using a magnetic field 

 to deflect and remove the slow-moving electrons present with 

 the a particles. He says, " 1 think these experiments un- 

 doubtedly show that the a particles do carry a positive 

 charge, and that the previous failures to detect this charge 

 were due to the masking action of the large number of 

 slow-moving electrons emitted from the plates." These 

 results, while they afford a welcome confirmation ol the con- 

 clusions drawn from the evidence of the magnetic and electrii 

 deviation suffered by the o rays, do not, to my mind, finally 

 settle the question. 



It must be admitted that the a particles in ordinary cir- 

 cumstances do carry a positive charge. Certain evidence, 

 however, seems to point to the conclusion that the a particle 

 at the moment of its expulsion from the parent atom i- 

 uncharged, and that it derives its positive charge from 

 secondary causes, independently of, and subsequent to, the 

 expulsion process. To (levl>ie a crucfal experiment which 



