May 14, 1908] 



NA TURB 



29 



" usuallv involves nothing more than making simple 

 qualitative tests for adulterants," by bringing to- 

 gether in one small book the best and simplest qual- 

 itative methods of detecting all the common sophisti- 

 cations of foodstuffs. 



As a collection of recipes the work is good ; in other 

 respects it commands but qualified admiration. For 

 the glorified cookery-book in chemical literature we 

 have no great liking,' and this compendium of " tests " 

 is little more. The numerous pitfalls which beset the 

 unwarv are rarelv indicated in the directions given ; 

 and the reasons 'for the various operations are left 

 for the operator to discover for himself. Now this 

 is well enough if the person using the book is already 

 a master of" his craft, knowing the pitfalls and how 

 to avoid them, cognisant of the why and wherefore 

 of his procedure, and only employing the work as a 

 convenient collection of notes wherewith to refresh 

 his memorv when applying the various processes. But 

 in the hands of the unpractised person, whether 

 >tudent or "inspector," it is quite another matter. 

 Differences of conditions, apparently slight, may lead 

 him whoUv astray. It would be well enough for the 

 enthusiastic student or teacher to test his breakfast 

 bacon for borax, or his morning milk for added water, 

 provided he does it merely for his private information ; 

 only in that case it would not benefit the pure-food 

 movement much. But if he is going to lodge a serious 

 complaint on the strength of his discoveries, it would 

 be well, also, first to have those discoveries confirmed 

 h\ a practised analyst. Otherwise there may arise 

 unpleasant references to the law of libel. 



The experiments are well selected and tersely de- 

 scribed. As a compendium of some of the best quali- 

 tative tests for ordinary food-adulterants the book will 

 be useful, especially to the man who already knows 

 how to apply the processes. C. S. 



AUitKdc Tables. Computed for Intervals of Four 

 Minutes between the Parallels of Latitude 0° and 

 30°, and Parallels of Declination 0° and 24°. De- 

 signed for the Determination of the Position Line at 

 all Hour .\ngles without Logarithmic Computation. 

 By Frederick Ball. Pp. xxxiii + 24S. (London: 

 J.' D. Potter, 1907.) Price 15X. net. 

 SiNXK the notice of the first part of this work appeared 

 in N.\TURE of February 20, the companion volume for 

 latitudes 0° to 30° has been published, making these 

 tables complete between the parallels of 60° N. and 

 <n>° S. Bv their means the navigator can with facility 

 ind rapidity determine his position by the observ- 

 ation of any heavenly body the declination of which does 

 not exceed' 24°, and, as the latitude and declination 

 are interchangeable in the tables, they are conse- 

 quentlv available for all stars up to 60° in declination 

 between 24° N. and 24° S. 



This valuable contribution to scientific navigation 

 ■will be appreciated bv all navigators who employ the 

 "' New Navigation "' — Captain Marcq St. Hilaire's 

 method — as a practical and direct help in saving the 

 tedious computation of the altitude required in the 

 problem. The tables will undoubtedly tend to popu- 

 larise that excellent method, which has hitherto been 

 neglected by so many navigators, mainly on account 

 of the lengthv calculations entailed, and more especi- 

 .'lUv when it is realised that their practical utility 

 equals their mathematical exactness. 



The introduction to each volume fully explains the 

 various uses of the tables, so that no difficulty need 

 be experienced when employing them. The book is 

 of a handy size and well bound, with clear type well 

 arranged and spaced, so that tfie navigator with but 

 little light and limited time will find a pleasure in 



using it. MlREMONT. 



NO. 201 1, VOL. 78] 



Logarithmic and Other Tables for Schools. By 

 Frank Castle. Pp. 36. (London : Macmillan and 

 Co., Ltd., 1908.) Price 6d. 

 The introduction of more practical methods in the 

 teaching of mathematics in schools has led to an in- 

 creasing demand for inexpensive tables of logarithms, 

 values of trigonometric functions, and other data 

 which pupils are now encouraged to use at quite an 

 earlv stage of their mathematical work. Mr. Castle 

 has compiled a series of fotir-figure tables which will 

 meet every need of mathematical classes in schools, 

 and be of great service in school laboratories. The 

 tables include logarithms and antilogarithms, natural 

 and logarithmic sines, cosines and tangents, degrees to 

 radians and radians to circular functions, hyperbolic 

 logarithms, powers, roots and reciprocals, and expo- 

 nential and hyperbolic functions. The type is cleat 

 and the style attractive, and these qualities, combined 

 with the wide scope and low price, should ensure a 

 wide popularity for the tables. 



Praise of a Simple Life. Edited by E. .\. Baker. 



Pp. X 4-258. (London : George Routledge and 



Sons, Ltd., n.d.) Price 2x. 6d. net. 

 Mr. B.aker has compiled a collection of extracts on 

 the theme of a life according to nature from classical 

 writers to the end of the eighteenth century. These 

 utterances are arranged in four sections, which the 

 editor calls respectively the antique world, the dawn 

 of a new age, the age of expansion, and the age of 

 reason. More than four-score authors are drawn 

 upon, so that the reader is provided with a diversity of 

 points of view. The volume is dainty, will go into 

 the pocket, and should b^ a favourite with readers 

 of poetic temperament. 



LETTERS TO THE EDITOR. 



)The Editor does not hold liimself 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 taken of anonymous communications.] 



On the Radio-activity of Potassium and other Alkali 

 Metals. 



In the course of some experiments made by them on the 

 radio-activity of a series of salts which had hitherto been 

 considered inactive, Messrs. Campbell and Wood (Proc. 

 Camb. Phil. Soc, vol. xiv., part i., p. 15, 1907) found 

 that potassium salts exhibited a radio-activity greater than 

 that of any other substance previously examined which did 

 not contain any of the so-called radio-active elements. 



In seeking for the source ol this activity, these experi- 

 menters found it impossible to separate out any active 

 impurity from the salts examined, and they were led by 

 the results of their investigation, which included measure- 

 ments on the activities of a limited number of the com- 

 pounds of potassium, to conclude that the activity 

 originated with the potassium itself, and was an atomic 

 property of that metal. 



In a later paper (Proc. Camb. Phil. Soc, vol. xiv., 

 part ii., iqoy) Campbell described some additional experi- 

 ments dealing with the character of the radiation emitted 

 by the potassium salts, and in concluding expressed the 

 opinion that the radiation consisted of B rays possessing 

 an average velocity less than tha* of the $ rays of 

 uranium. 



During the last few months the writer, in collaboration 

 with Mr. W. T. Kennedy, has made, in the Physical 

 Laboratory at Toronto, a close examination of the radio- 

 activity of a large number of potassium and other salts, 

 and while the results of this examination confirm the dis- 

 covery of Campbell and Wood that potassium salts 

 generally possess an exceptionally high activity and emit 

 a radiation possessing considerable penetrating power, they 



