28 



NA TL T RE 



[November 9, 1905 



arcs, the calculation of light for interior and exterior 

 places, .md concludes with tables giving the reflect- 

 ing powers of various surfaces, and the horizontal 

 illumination required for different places. 



The last part illustrates the construction and 

 application of auxiliary plant, including steadying 

 resistances, choking coils, transformers, safety appli 

 ances, &c. 



The book is intended chiefly for students. As such 

 it might be improved by including a little more of 

 the theory of the arc, of which the author says prac- 

 tically nothing. Very few engineering students will 

 find sufficient time to study works such as " The 

 Electric Arc," by Mrs. Ayrton, unless they make the 

 study of arc lamps their speciality. 



The second part will form a good advertisement 

 for the A. E.G. Company's lamps, as most of the dia- 

 grams represent designs made by this firm. But 

 although it is quite easy to deduct the principles of 

 action of other lamps from the diagrams given, one 

 does not like to see in a text-book the productions 

 of one manufacturer only, as it reduces the work 

 almost to a catalogue. Of great interest is Foster's 

 hot-wire arc lam]), although its commercial value has 

 vet to be proved. 



The most useful part of the book is the third one, 

 which will be welcomed by many students who are 

 able to read German. Also the fourth part contains 

 much useful matter. 



The book is practically free from printer's errors. 

 The few which occur may easily be detected by even 

 the most elementary reader. 



Taken as a whole, the pamphlet will be found a 

 useful addition to electrical engineering literature. 



H. BOHLE. 



Transactions of the South African Pliilosophical 

 Society. Vol. xv. Part v. Catalogue of Printed 

 Books, Papers, and Maps relating to the Geology 

 and Mineralogy of South Africa to December 31, 

 1904. By Miss M. Wilman. Pp. 283-467. (Cape 

 Town, 1005.) Price 12s. 6d. 

 This excellent bibliography represents months of 

 patient labour spent on a bewildering but necessary 

 task, and now happilv carried to a successful termin- 

 ation. The whole civilised world appears to have had 

 something to say on African geology. The labour 

 entailed in drawing up these lists, which easily super- 

 sede all others, will therefore be obvious. The 

 author has had, indeed, to exercise considerable 

 acumen in discarding numerous papers, &c, often 

 containing mere references to geologv, in order to 

 bring the lists even within their present compass. 

 As it is, a few works, since they are mentioned in 

 earlier lists, have had to be included, although they 

 add little to geological literature. The title is 

 generallv sufficient to warn the inquirer. 



Part i. deals with works on the general geologj of 

 South Africa, part ii. contains a list of geological 

 maps, while part iii. is exclusively devoted to works 

 on meteorites. The print is clear, and the names of 

 authors are distinctlv marked in Clarendon type. 



W. G. 

 Problems in Practical Physics. By F. R. Pearson, 

 M.A. Pp. 30. (Edinburgh and Eondon : Oliver 

 and Boyd, 1905.) Price 6d. 

 These problems ate intended to accompany practical 

 work in a laboratory, and should serve to give practice 

 in working out results. The subjects on which 

 examples for solution are set include the parts of 

 physical science studied in a first year's course. 

 Teachers "I mathematics may find the booklet useful, 

 as it will provide interesting applications of simple 

 mathematical principles to practical problems coming 

 within simple laboratory experience. 



NO. 1880 \OL. 73"! 



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 taken of anonymous communications.] 



Terminology in Electro-physiology. 



My attention has been directed to a letter in your 

 columns (p. 5) commenting upon the ambiguous use made 

 in physiological literature of two opposed terms, " nega- 

 tive " and "electropositive." 



To me also it seems a misfortune that this ambiguity 

 has ever arisen, nor do I see any necessity why it should 

 be allowed to persist. There is no obvious reason why, in 

 scientific papers, the terminology of the physicist should 

 not be adhered to. The " negativity " of a point is de- 

 tected by means of the current which flows towards it, or 

 tends to flow towards it, through some form of external 

 indicator connecting it to the point which is spoken of as 

 " positive." These terms, and these terms alone, 

 adequately express the fads of all the experimental observ- 

 ations made. Any other terminology differing from this 

 is necessarily based upon some inference as to the mode 

 of causation of the currents detected. Since it is the 

 causation of these currents which is the main crux of the 

 research work undertaken in this subject, the admission 

 of sue h an inference seems a certain road to the confusion 

 of ideas. 



In all cases where an effort has to be made to carry 

 home to an audience the more exact ideas existing in the 

 author's brain, in all cases where parables are not only 

 admissible but necessary, I think the terms suggested by 

 Or. Waller are of extreme value. Anyone acquainted with 

 the explanatory use he has made of them in his " Animal 

 Electricity " will agree. Whilst sincerely admiring his 

 profoundly (lexer method of administering large doses of 

 knowledge by means of this and similar parables, I have 

 observed two things. In the first place, that duller wits, 

 hugely mistaken, sometimes assess his knowledge' as 

 mainly one of parables. In the second place, lien less 

 expert persons are apt to carry conclusions derived from 

 parables to a bitter and unjustifiable extremity. 



Sheffield University. • J. S. MacDonald. 



The Leonid Meteors, 1905 



The remarkable displays of these meteors observed in 

 1903 and 1904 may naturally raise the expectation as to 

 whether the approaching Leonid epoch will exhibit an 

 abundant fall of shooting stars. Observers, it is true, will 

 have to contend against the impediment offered by the 

 light of the gibbous moon; but, it may be remarked, this 

 can only affect the smaller class of meteors, as the brilliant 

 apparitions of 1866, 1867, and 1S80 were witnessed at a 

 similar phase of our satellite. 



The Leonid events of the pasl two years afford striking 

 illustrations of the meteoric cycle of nineteen years, being 

 associated respectively with the Leonid meteor displ.es ,,( 

 [865 and 1866, and the present November gives ample 

 premise of furnishing another example of the same period. 



Unlike tin- I. '.mid falls of 1865 and [866, that of 

 November 14, 181,7, was brilliantly reproduced on the first 

 completion of this cycle on the morning of November 15, 

 1S86, the spectacle being ,,i extraordinary splendour 

 (Nature, vol. lxi., p. 491). 



The Leonid maximum of 1005 will fall on the night of 

 November 15, and, according to calculations by (he present 

 writer, will be visible both over Europe and America. 

 The shower will be of second-class order, that of 1866 

 being regarded as of first, and will commence early in the 

 night, the first maximum occurring on November 15 

 1 ile I..M.T. From this hour up to about thro o'clock 

 on the morning of November in the Leonids will probably 

 gradually increase in numbers, the second maximum of 

 the night Incoming due on November 15. t,sh. 10m. The 

 final maximum on November 1^ occurs at jih., and will 

 consequent!) be visible to American observers only. 



1 (ublin. John R. Henry. 



