324 



NA TURE 



[January 31, 1901" 



success. He does not use the plan of questioning to the 

 excess characteristic of some other authors of recent text- 

 books of chemistry ; and his book has some special features 

 which make it worth adoption in elementary classes in 

 schools and colleges. The intelligent order in which the 

 subjects are dealt with, and the attention given to in- 

 dustrial processes, are particularly worthy of credit. 



Die Phoiographie iin Diensie der Himmelskunde. Von 

 Dr. Karl Kostersitz. Pp. 53. (Wien : Carl Gerold's 

 Sohn, 1900.) 



This short monograph is a reprint of a lecture given by 

 Dr. Kostersitz before the Vienna Photographic Society. 

 The author describes in a somewhat general way the 

 results that have been obtained by applying the camera 

 to the end of a telescope and turning it towards the 

 lieavens. We are thus introduced to the appearance of 

 ■ the general features of the sun in and out of an eclipse, 

 and a brief reference to the planets and asteroids as 

 shown us by photography. Meteor photography is more 

 fally described, and the author here gives two illustrations 

 showing trails as photographed by him. The method of 

 determining the relative brightness of stars by photo- 

 graphing them slightly out of focus is described, and a 

 few words are written about the photography of the 

 Milky Way. The illustrations, which are numerous and 

 good, are chiefly from Scheiner's "Photographic der 

 Gestirne," there being two excellent heliogravures show- 

 ing the nebula of Orion and Barnard's Milky Way. 



The last portion of the book is devoted to the publi- 

 cation of twelve replies that were received from different 

 authorities in answer to a suggestion, proposed by the 

 author, of erecting an observatory on the top of the 

 " Schneeberg." These form interesting reading, although 

 they hardly have any connection with the subject-matter 

 of the book itself. 



Although the monograph does not pretend to be com- 

 plete, yet it gives the reader an idea of the important 

 part played by photography in astronomy. 



Die Sdkular- Verlegung der Magnetischen Axe derErde. 

 Von W. van Bemmelen. (Observations made at the 

 Royal Magnetical and Meteorological Observatory at 

 Batavia.) Vol. xxii. Appendix i. Pp.30. 



This is an attempt to trace the position of the earth's 

 magnetic axis during the last three centuries, on the 

 supposition that a knowledge of magnetic declination is 

 sufficient to determine the direction of its axis. Great 

 circles drawn through different points, and coincident at 

 these points with the magnetic meridians, would inter- 

 sect in the poles of the magnetic axis, if the earth were a 

 uniformly magnetised sphere. As this is not the case, 

 the circles all pass through an arctic and an antarctic 

 region instead of through two points, and Mr. van Bem- 

 melen calculates by the method of least squares the point 

 in each region which is nearest to the circles. The two 

 points thus found he takes for the intersections of the 

 magnetic axis with the earth's surface. The reader must 

 be referred to the original for the clever manner in which 

 the calculations are simplified and carried out. The 

 method is first tested for the year 1885, when it is found 

 that the magnetic axis, calculated in this fashion, agrees 

 closely with that derived from the more rigorous analysis 

 of Neumayer and Ad. Schmidt. It is then applied to the 

 declination values for the years 1600, 1650, 1750, 1770 

 and 1842, and the author draws from the results thus 

 obtained the conclusion that the magnetic axis does not 

 1 evolve round the geographical axis, but that there seems 

 to be a tendency to revolve round Nordenskjold's aurora 

 pole. A doubt must necessarily arise in the mind of the 

 reader as to how far the older observations are suffi- 

 iently numerous and correct to allow any certain con- 

 clusions to be drawn from them. Any one looking at 

 Neumayer's Atlas (Berghaus) of Terrestrial Magnetism 



NO. I 63 I, VOL. 63] 



will be struck at once by the fact that the distribution of 

 magnetic declination in the year 1600 is represented as- 

 being widely different from that of a uniformly magnetised 

 sphere. We must conclude that either the observations 

 were not sufficiently accurate to give us a correct picture, 

 or that the earth differed much more from a uniformly 

 magnetised sphere at that time than it does now. As 

 V. Bemmelen has only tested his method at a time when the 

 deviations from uniformity were small, there is consider- 

 able doubt whether equally good results would be obtained 

 with irregular magnetisation. The work, meritorious and 

 interesting as it is, cannot, therefore, be said to have led ta 

 any conclusion which can be accepted without further 

 evidence. 



The Theory of Commutation. By C. C. Hawkins. Pp. 81. 

 (London : J. Tucker, no date.) Pl-ice2J. bd. 



In this pamphlet Mr. Hawkins enters into a complete 

 mathematical investigation of the reactions occurring 

 during the process of commutation in continuous current 

 dynamos. The author first examines the case in which 

 the contact resistance of the brushes is neglected, and 

 then proceeds to give a complete solution of the equation 

 for the current in the short-circuited coil, taking into 

 account this resistance. This solution is due to Prof. 

 Arnold and Dr. G. Mie, but our thanks are due to Mr. 

 Hawkins for introducing it into England and for pointing 

 out its practical bearings. Mr. Hawkins show-s that the 

 contact resistance is of the greatest importance in pre- 

 venting sparking ; the employment of carbon as the 

 material of the brushes is consequently desirable, since 

 the contact resistance of carbon is about fifteen times 

 that of copper. Allowing for the fact that the surface 

 needed to collect the same current must be about five 

 times as great with carbon as with copper, the carbon 

 brushes are still, approximately, three times as good as 

 copper. The author also points out the other considera- 

 tions affecting sparking, and goes fully into the question- 

 how it may be best avoided, both in dynamos and motors. 

 The mathematical investigation is made clearer by the 

 application of the results to a practical case, and by a 

 careful explanation of the physical interpretation of the 

 equations. 



Albmn of Papiia. Types II. North New Guinea^ 

 Bismarck Archipelago, German Salomon Islands. 

 By Dr. A. B. Meyer and R. Parkinson. About 550 

 figures on 53 plates in heliotype. (Dresden: Stengel 

 and Co., 1900.) Price ^os. 



Through the energy and skill of Mr. Parkinson, Dr. 

 Meyer has been enabled to publish a second album of 

 photographs illustrating Melanesian ethnology. The 

 present album supplements the first one, which was pub- 

 lished in 1894, and is now out of print. The photographs 

 are well taken, and give us instructive glimpses of native 

 life. The short explanation of each plate is printed in 

 German and English, and these little accounts frequently 

 contain notes of great interest, and there are helpful 

 references to previous publications. There is a photo- 

 graph (pi. xxiii. 2) of a girl playing the " pangolo." In 

 his admirable memoir on " The Natural History of the 

 Musical Bow," Mr. H. Balfour gives an account of the 

 playing of this interesting musical instrument, which 

 differs from that described by Meyer and Parkinson, the 

 original account of the pangolo, by Dr. O. Finsch, being 

 insufficient. Mr. Balfour evidently read into Finsch's 

 figure more than it was intended to convey. 



Albums such as these are of very great service ta 

 students at home, as good illustrations are much more 

 readily grasped than are long verbal descriptions, and 

 we hope that other albums will follow in due course. 

 This is not the first time that Mr. Parkinson's labours in 

 ethnology have been recognised in Nature, and we 

 only wish that some of our British residents and traders. 



