REVIEWS 473 



It illustrates in a remarkable way the power of modern photographic methods : 

 the observations were commenced in the middle of 1914 and up to 1920 260 

 parallaxes of a high order of accuracy had been determined. In addition, 

 numerous plates of other stars have already been obtained, so that probably 

 about 100 determinations per year can be added to the series. This work has 

 been accomplished with a single telescope and a small staff, who have not 

 only taken the photographs but have also measured and reduced them. The 

 results testify to the industry, organising ability, and enthusiasm of Prof. 

 S. A. Mitchell, who is heartily to be congratulated upon the skill and perse- 

 verance with which he has carried on his programme of work. 



The methods of observations follow generally upon the lines indicated by 

 Schlesinger in his epoch-making work at the Allegheny Observatory. They 

 are fully outlined in the preface to this volume, which contains an interesting 

 account of the history and methods of parallax determination ; it can be 

 recommended to anyone desiring information upon the subject. With 

 modern methods, the accidental error of observation can be reduced to some- 

 what less than one-hundredth of a second of arc, but it is not so easy to ensure 

 that systematic errors have been entirely eliminated. Examination of the 

 Leander McCormick results indicates that the systematic errors are extremely 

 small — of the order of a few thousands of a second, so that the series may 

 be regarded as one of the most accurate as well as one of the longest which has 

 emanated from a single observatory. H. S. J. 



Simple Lessons on the Weather. By E. Stenhquse, B.Sc. [Pp. viii + 135. 



with 12 plates and 62 figures.] (London: Methuen & Co.) 



This book explains some of the physical processes of meteorology in a simple 

 and lucid manner, and is primarily a school textbook ; it can, however, also 

 be read with advantage by anyone interested in the subject who does not 

 possess much scientific knowledge. 



There are twenty-eight chapters altogether, dealing with such subjects as 

 the formation of rain and hail, fog, dew, etc., and the measurement of rainfall 

 and sunshine. There is even a little astronomy included to help to explain 

 the seasonal changes of the weather, A good feature is the frequent use of 

 " isopleth " diagrams for displaying a large mass of statistical information in 

 a very clear manner, for the principle underlying these diagrams must in any 

 case be mastered by those who wish to understand modern synoptic-charts 

 and weather forecasting. 



Included among the twelve plates are some excellent cloud photographs, 

 and others of great beauty representing snow, rime, hoar frost, and hail. 



E. V. N. 



PHYSICS 



British (Terra Nova) Artarctic Expedition, 1910-13 : Terrestrial Magnetism. 



By Charles Chree, M.A., Sc.D., LL.D., F.R.S. [Pp.xii + 55°. 

 with four figures and 60 plates.] (London: Harrison & Sons, 1921.) 



This volume, the cost of the preparation and publication of which has been 

 defrayed from the fund which was raised by public subscription in memory 

 of Captain R. F. Scott and his companions, contains an elaborate discussion 

 of the magnetic observations obtained on the Antarctic Expedition of 1910- 

 13. Although an enormous amount of work has been involved in com- 

 piling this volume, the results would have been available at an earlier date 

 but for the war ; in spite of the delay so caused, the publication is more 

 prompt than in the case of some similar expeditions. Frequently the delay 

 in publication is so great that the value of the scientific results obtained 

 is materially reduced, and a plea may be put forward for an endeavour 



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