December i, 192 i] 



NATURE 



431 



full well that the same tale may be told of you a 

 few months later." 



(3) " Intemperance in the quantity of food taken 

 is almost the rule. Adults eat far too much." 



(4) "Things medical and gruesome have a singu- 

 lar attraction for many people. . . . To talk of 

 diseases is a sort of Arabian night's entertainment 

 to which no discreet nurse will lend her talents." 



For graver and more intimate converse with 

 Osier's mind, we have this anthology as our com- 

 panion — a book worth reading, worth buying. 



Our Bookshelf. 



The Position in Space of the Aurora Polaris, from 

 Observations made at the Haldde Observatory, 

 1913-14. By L. Vegard and O. Krogness. 

 (Geofysiske Publicationer, vol. i, No. i.) 

 Pp. vii+ 172 + plates. (Kristiania : A. W. 

 Br<^ggers Boktrj-kkeri A/S, 1920.) 



This is an elaborate account of observations made 

 to determine the height of the aurora, by the 

 method originally devised by Stormer, and used 

 by him in 1910. The method consists in photo- 

 graphing the aurora simultaneously at two stations 

 some miles apart, and determining its parallactic 

 shift relative to the stars. In the present work 

 the authors employed a base line of 125 kilo- 

 metres, much larger than the base of only 45 

 kilometres used by Stormer in his first experi- 

 ments. 



The lowest height of the aurora is a question 

 of long-standing controversy. Many of the older 

 observers thought that it reached on occasion to 

 the ground level, but Dr. Simpson's observations 

 in the Antarctic led him to think that this was an 

 illusion, and certainly it seems very improbable 

 if the theories now current of the origin of the 

 aurora in corpuscular rays are to stand. Stormer 

 never found anything lower than about 40 kilo- 

 metres, and the present work seems to indicate 

 that the lowest values found by him were erro- 

 neous, the base line employed not being long 

 enough for accuracy. Vegard and Krogness find 

 the lower limit to range from 73 to 166 kilometres. 

 They find an indication of two maxima in the 

 height distribution curve, at 100 and 106 kilo- 

 metres respectively, and incline strongly to believe 

 that these are real, and due to the presence of two 

 kinds of corpuscular rays. 



The methods of measurement and reduction are 

 set out in great detail, and a large number of 

 photographs are reproduced. R. 



Dairy Bacteriology. By Prof. Orla-Jensen. 

 Translated from the second Danish edition, 

 with Additions and Revisions. Bv P. S. Arup. 

 Pp. xii+i8o. (London: J. and'A. Churchill, 

 1921.) 185. net. 



This book has already passed through two 

 editions in Denmark, and is now translated into 

 English. It will be found to present a useful sum- 

 mary of the subject for the dair\' worker, giving 

 NO. 2718, VOL. 108] 



him information that will be of value in his routine 

 work, and will help him in coping with the 

 troubles that periodically arise in dealing with 

 farm products. 



Milk fresh from healthy cows contains a few 

 organisms derived mainly from the air, the udder, 

 and the teats ; these are nearly all micro-cocci and 

 sarcina forms, most of which are without action 

 on the milk, though a few acidify and peptonise 

 it. Milk which has been less carefully handled 

 is liable to contain a great variety of organisms — 

 coli, aerogenes, and others from the dung; fluor- 

 escent bacteria from the water used for rinsing 

 the pails ; and others from the bedding, stable 

 dust, etc. The American "certified milk" con- 

 tains less than 10,000 of these organisms per c.c. ; 

 this keeps well. The author gives other figures 

 for other samples, running up to hundreds of 

 millions per c.c. There is a good account of milk 

 preservation and treatment. 



Mitteilungen der Naturforschenden Gesellschaft in 

 Bern aus dem Jahre 1919. Pp. Ixxv -1-2314- 

 Tafel 5. (Bern : K. J, Wyss Erben, 1920.) 

 The scientific communications published in this 

 volume are mainly of local interest. Prof. Ed. 

 Fischer chronicles additions to the list of species 

 in the flora of Berne which have been noted in 

 the past ten years ; a large number are aliens 

 which have been introduced in various ways. The 

 most important communication in point of length 

 is by Werner Liidi on "The Succession of Plant 

 Associations," an ecological study of the vegeta- 

 tion of the Bernese Oberland, with special refer- 

 ence to the Lauterbrunnen valley. Dr. R. Stager 

 describes some myrmecological obser\-ations on 

 the Belalp at more than 2000 metres elevation, 

 in which he notes the distribution of the seeds of 

 Thesium alpinum by two species of ant. 

 E. Gaumann gives an account of the occurrence 

 and area of distribution in Switzerland of the 

 species of the parasitic fungus genus Peronospora, 

 and there is also a paper on the etiology of the 

 " grippe " by Dr. Sahli. 



The Elements of Direct-current Electrical Engi- 

 neering. By H. F. Trewman and G. E. Cond- 

 liffe. Pp. vii4-2ig. (London : Sir Isaac Pitman 

 and Sons, Ltd., 192 1.) 7s. 6d. net. 

 The object of this addition to the many electrical 

 text-books is to bridge the gap between elementary 

 handbooks and treatises on dynamo design. The 

 general principles of induced currents and electro- 

 magnetism are briefly recapitulated, a few of the 

 more common instruments are described, and the 

 main features of the direct-current dynamo and 

 motor are treated in a practical wav. We are 

 pleased that the authors have the courage to use 

 the calculus in such an elementary work where it 

 simplifies proofs, for, as they rightly point out, "it 

 is essential to all students of engineering." The 

 treatment is apt to be a little too sketchy for the 

 second-year student for whom the work is in- 

 tended, and future editions should remove such 

 blemishes as "electric-motive force." 



