REVIEWS 333 



being absent, it is not necessary that the position should be determined 

 with an accuracy exceeding ten miles. This enables the observations to 

 be reduced with the aid of such appliances as the Veater diagram or the 

 Bygrave slide rule, so avoiding the use of logarithms. 



The author explains in some detail the determination of position from 

 astronomical observations, using the Sumner line method and these mechani- 

 cal methods of reduction. The principles and methods of dead reckoning 

 navigation — in which two inventions by the author, the wind gauge bear- 

 ing plate and the course-setting sight, are of considerable use — are dealt 

 with, and also the determination of position by the use of directional wire- 

 less, with the method of plotting the directions on a Mercator chart. 



The book is written in a straightforward, simple style, and can be 

 thoroughly recommended. 



H. S. J. 



The Principles of Aerography. By Alexander McAdie, Professor of 

 Meteorology, Harvard University, and Director of the Blue Hill 

 Observatory. [Pp. xii + 318, with 112 figures.] (London: George 

 G. Harrap & Co., 1917. Price 21s. net.) 



The author, in his preface, makes a distinction between meteorology and 

 what he terms aerography, the former being the science of recording diverse 

 atmospheric conditions, the latter resembling geography in its widest sense, 

 and being concerned with utilising the knowledge gained by meteorology in 

 insuring human safety and expediting progress. The book, therefore, aims 

 at giving prominence to recent work in exploration of the air, an account of 

 much of which has hitherto only been available in scientific publications. 

 Reference is made to the work of Shaw, Dines, Cave, and other modern in- 

 vestigators, and Simpson's theory of thunderstorms is given in considerable 

 detail. It is unfortunate that the important work of G. I. Taylor on tur- 

 bulence in the atmosphere, Rayleigh's investigation of the dynamics of 

 revolving fluid in the atmosphere, and much of Shaw's work on cyclones, 

 are just too recent to be included, so that in some respects the present state 

 of knowledge is not well represented. Wherever possible, the practical 

 application of results is emphasised, a feature which is, unfortunately, too 

 often lacking in textbooks on meteorology. Thus the methods of fore- 

 casting storms and frosts are dealt with in detail, and in the discussion of 

 thunderstorms are included details of methods of lightning protection. 



Much attention is given to cloud forms and the thermodynamics of 

 their formation, and an attempt is made to classify them according to their 

 origin rather than according to their appearance. The older plan has much 

 to recommend it, and the proposed changes are not likely to meet with 

 general acceptance. In connection with clouds, the author rightly empha- 

 sises the unsatisfactoriness of cloud observations being made at most obser- 

 vatories only twice in twenty-four hours — say, 8 a.m. and 8 p.m. Such 

 records have little value when information as to the average cloudiness at, 

 say, midday is required. More than once, eclipse expeditions have gone 

 to unsuitable stations owing to the available cloud observations giving mis- 

 leading information. 



The author makes a special point of using absolute units throughout. 

 This step is to be welcomed. Their general use in meteorological textbooks^ 

 will greatly help to displace the old arbitrary units. 



The book is very well indexed and illustrated, and, in spite of somewhat 

 ambiguous phrasing in several places, can be thoroughly recommended. It 

 may be noted that at the top of p. 32 the reciprocal of flattening of the 

 earth is given as 1/29-4 instead of 1/294. 



H S. J. 



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