QCTCIIER 2 1, 1909] 



NA TURE 



48: 



As it is, tlie initiated reader must be amazed at the 

 amount of useful information wliicli has been com- 

 pressed into ^50 small octavo pages. In every branch 

 and sub-branch of mathematics all the fundamental 

 definitions, theorems, and formulae have been given, 

 sufficient explanation being added to make the whole 

 intelligible to the average mathematician. A similar 

 plan has been adopted for the physical and astro- 

 nomical parts, numerous tables of constants being 

 given, as well as descriptions of apparatus. .\t the 

 end of the book is a useful list of mathematical and 

 physical books and periodicals. 



We have noticed a few errata, e.g. p. 44, the first 

 theorem of the mean is incorrectly stated, and p. 46, 



I dx is equal to 7r/3 only if b>o. These, 



-' -'^ . 



however, are slight blemishes, inevitable in a first 



issue. In conclusion, we wish the " Taschenbuch " 



all the success it undoubtedlv deserves. 



OVR BOOK SHELF. 



An Introduction to the Science of Radio-activity. By 

 C. W. Raffety. Pp. xii + 208. (London : 'Long- 

 mans, Green and Co., 1909.) Price 45. 6d. net. 

 The aim of this book is to present a concise and 

 popular account of the properties of the radio-active 

 elements and of the theoretical conceptions which are 

 involved in the study of radio-active phenomena. 

 With this object in view, the treatment throughout 

 is purely descriptive, and no attempt is made to 

 develop the mathematical side of the subject. Never- 

 theless, the author has succeeded in describing and 

 discussing most clearly the various phenomena of 

 radio-activity. 



The book is divided into three parts. The first 

 part is descriptive, and, after a general note on the 

 radio-active elements, is devoted to the consideration 

 of the nature of the various radiations emitted by 

 radio-active bodies. The characteristics of the a, (s, 

 and y radiations are carefully explained. 



In the second part of the book the author deals 

 with the subject of radio-active transformations, and 

 describes in detail the various disintegration products 

 produced from thorium, uranium, and radium. 

 Chapter iv. in this section contains an account of 

 the theorv of atomic structure from the electron point 

 of view. The evidence drawn from various pheno- 

 mena shows large variations in the number of electrons 

 associated in the atom. The author gives the numbers 

 calculated from experiments on kathode rays. The 

 third part of the book is devoted to kathode, canal, 

 and X-ravs, and gives experimental details which 

 should enable an amateur to carry out successfully 

 a number of experiments with a small amount of 

 apparatus. A feature of the book is the appendi.x, in 

 which the author has collected and tabulated the 

 physical constants of the n, /3, and y rays, the pro- 

 ducts of decay of tBe radio-active elements, with their 

 rates of decay, and the absorption coefficients of the 

 radiations emitted by the radio-active bodies. 



Altogether the book can be heartily recoinmended 

 to mathematical, as well as non-mathematical, readers 

 who desire an acquaintance with the subject of radio- 

 activity. 



British Mountain Climbs. Bv George D. Abraham. 

 Pp. xvi-i-448. (London : Mills and Boon, Ltd., 

 T909.) Price ys. 6d. net. 

 Mr. Abraham here provides the lover of British 

 mountaineering with a conveniently small and 

 concise guide to the British rock-climbs. The 



NO. 2CS6, VOL. 81] 



climbs are grouped around the most convenient 

 centres, and detailed instructions . as to how 

 to perform the various expeditions safely are 

 given. The book is provided with eighteen illustra- 

 tions and twenty-one outline drawings, showing the 

 principal routes.' It is written in a bright, interest- 

 ing stvle, and is sure to become a favourite among 

 mountaineers who are willing to learn from it the 

 beauties and difficulties of climbing at home. 



The Pond and other Stories. By Carl Ewald. Trans- 

 lated from the Danish by .Alexander Teixeira de 

 Mattos. Pp. 320. (London : Everett and Co., 

 1909.) Price 6s. net. 

 This series of eleven stories deals with animal and 

 plant life in a way dear to children. The birds and 

 beasts talk to one another, and incidentally supply the 

 reader with many familiar facts of nature-study. 

 Each storv is provided with a good illustration, and 

 the easv colloquial English of the translator will be 

 understood by the young children for whom the book 

 is evidentlv intended. 



LETTERS TO THE EDITOR. 



[The Editor does not hold 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 tal;cn of anonymous communications.] 



Magnetic Storms. 



Dr. Curee contends that magnetic observations have 

 now reached a high pitch of perfection, and that their dis- 

 cussion is not lightly to be un^iertaken by outsiders. That 

 is no doubt so, and there must be many features about 

 magnetic storms which are known only to experts. But 

 when we find experts in doubt on such a fundamental 

 matter as whether the cause of those storms is to be 

 found in the sun or in the earth, it appears to be worth 

 while to emphasise some comparatively simple and funda- 

 mental considerations which may possibly have become 

 rather covered up by a mass of information. 



The simple points' that I venture to emphasise, with all 

 due deference to specialists, are : — 



(i) That by reason of the high temperature and con- 

 vulsions of the sun it is almost bound to emit electric 

 projectiles. 



{2) That when the visible sign of a solar eruption is 

 aimed at tlie earth, magnetic storms are often felt, while 

 they are not so frequently experienced from eruptions the 

 emissions of which may be reasonably supposed likely to 

 miss the earth. 



(3) That, taking into account the varying aspect of 

 places on the earth to a solar beam, such a stream of 

 particles is well qualified to produce changes in all the 

 magnetic elements during the course of a day — even though 

 deflection bv magnetic lines, and the effect of currents 

 induced in the conducting layer of the upper atmosphere, 

 were ignored. (1 do not say that the details of a storm 

 fit so greatly simplified a theory.) 



(4) That a great beam of this kind is not likely to be 

 uniform, but may be supposed to contain rays of special 

 intensity, the passage of which will cause well-marked and 

 rapid reversals, such as are observed. 



(Of course, I never thought that the recent storm was 

 over in fifteen minutes ; it was common knowledge that it 

 lasted for hours. I must have expressed myself badly if 

 I conveved such an idea.) 



(5) That detection, in storm-recurrence, of any periodicity 

 which corresponds at all closely with the period of the 

 sun's relative axial rotation — such as is maintained by Mr. 

 Maunder and apparently half admitted by Dr. Schuster — 

 would surely be conclusive as to something solar in origin. 



(6) And, especially, that simple calculations from known 

 laboratorv data show that the magnitude of the effect 

 observed is not unreasonably great to attribute to local 

 solar radio-active emissions. 



Hesitation as to the truth of this last proposition was. 



