NA TURE 



575 



THURSDAY, FEBRUARY 29, 1912. 



THE PRINCIPLES OF WEATHER 

 FORECASTING. 

 Forecasting Weather. By Dr. W. N. Shaw, F.R.S. 

 Fully illustrated with maps, charts, and diagrams. 

 Pp. xxviii + 380. (London : Constable and Com- 

 pany, Ltd., 1911-) Price 125. 6d. net. 

 THE text-book on "Weather" published by the 

 late Hon. Ralph Abercromby in 1885 generalised 

 the practice in forecasting which had gradually estab- 

 lished itself in the Meteorological Office. The recog- 

 nition in that book of types of pressure distribution 

 associated with distinctive characteristics of wind, 

 temperature, and rain, gave definiteness to the con- 

 ceptions of cyclones, anticyclones, wedges, and V- 

 depressions, and impressed on the minds of the last 

 generation the dominance of atmospheric pressure 

 over all atmospheric changes. Abercromby wrote 

 with the enthusiasm of lively faith. He believed in 

 cyclones and anticyclones as powers which made the 

 weather — great, simple, and straightforward entities, 

 the ways of which were almost fully known, and 

 only a little additional knowledge required to make 

 the prediction of weather definite and precise. 



Recent meteorological researches at home and 

 abroad have gradually involved meteorologists in an 

 atmosphere of doubt as to the simplicity and the cer- 

 tainty of the relations of weather and pressure dis- 

 tribution. During his eleven years' labours as 

 director of the Meteorological Office, Dr. Shaw has 

 done much to initiate and encourage research into 

 the problems most vital to weather forecasting, and 

 the keenest anticipations have been formed as to the 

 nature of the book now before us. In one way we 

 are disappointed ; Dr. Shaw has not attacked the 

 Victorian certainties with the vigour of an iconoclast, 

 nor proclaimed a finished system of new beliefs. He 

 recognises the old ideas as idols, but he speaks of 

 them respectfully, not crushingly. He adopts a depre- 

 cating tone, indeed, as of one who knows better, and 

 insinuates the well-founded doubts which will enable 

 every candid meteorological mind to recognise its latent 

 idolatry and re-clothe the cyclonic Dagon or remove 

 him quietly out of his place. The book is adapted for 

 a transitional state of mind, ready to abandon the 

 early ways as soon as the larger light is clear enough 

 to make the new path plain, and that is the state of 

 mind of all thoughtful meteorologists ; hence it is 

 suggestive rather than didactic, and stimulating rather 

 than systematic. The main value of the work seems 

 to us to lie in the definite formulation of the results 

 of the recent researches carried on under the auspices 

 of the Meteorological Office, and still in progress, 

 researches which bid fair to reorganise the physical 

 basis of weather study, and to make possible a real 

 manual of weather forecasting at some future date. 

 The actuality of the present book is its chief attraction, 

 the reader being brought right to the front of ad- 

 vancing knowledge of weather conditions, and any 

 defects it may possess are defects of that great 

 quality. 



NO. 2209, VOL. 88] 



Dr. Shaw, as we have hinted already, does not 

 worship the conventional cyclone and anticyclone as 

 the creators and controllers of weather ; he shares 

 Prof. Hann's view that these isobaric forms are them- 

 selves produced as incidents in the great streams of 

 air which carry on the larger circulation of the atmo- 

 sphere, and he leads towards the recognition of sub- 

 stantial air-currents of diverse origin flowing in 

 various directions, meeting, and passing in various 

 planes at different angles, as the true causes of 

 weather. He treats moving air in accordance with 

 the well-known principles of physics, and endeavours 

 to establish the dynamical or thermodynamical ante- 

 cedents of the meteorological phenomena con- 

 cerned in weather. The work is one of immense 

 difficulty; few men of science would have the courage 

 to attempt it, and we are satisfied that no one having 

 undertaken such a task could have carried It out in 

 a more satisfactory way or with a more effective 

 result than Dr. Shaw has achieved. In the introduc- 

 tion he makes much of the difficulty of the long- 

 abused British units retained by English-speaking 

 meteorologists in both hemispheres, and he outlines 

 a modification of the C.G.S. system which would, he 

 believes, greatly simplify research and exposition. He 

 does not recommend the metric system as used by 

 Continental meteorologists ; but a derived system 

 which has the high moral advantage of requiring to 

 be learnt equally by our Continental friends and by 

 ourselves, a sort of arithmetical Esperanto. Tempera- 

 ture is to be expressed in centigrade degrees, but 

 from the absolute zero, so that ice melts at 273° and 

 water boils at 373°. Pressure is to be expressed in 

 fractions of the "C.G.S. atmosphere of 1,000,000 

 dynes per square centimetre," which corresponds to 

 the normal pressure, not at sea-level, but at an alti- 

 tude of 106 metres. The decimalisation of measures 

 of time and arc are not suggested, so that the scheme 

 lacks the roundness of theoretical perfection. In 

 practice, so far as this book is concerned, the new 

 system has superseded nothing, for the maps "on 

 which," the author too modestly says, " the book is 

 mainlv dependent," are for the most part expressed 

 in Fahrenheit degrees, inches, and Beaufort wind 

 forces. We confess that we do not share Dr. Shaw's 

 enthusiasm for the new system, but it is one of those 

 matters in which the advice of Gamaliel can well be 

 followed, and we do not raise a voice against it. 



•'Forecasting Weather" is treated in eighteen 

 chapters, of which the first five deal with synoptic 

 charts, the relation of winds to isobars, a statement of 

 Abercromby's view of the order of weather-changes 

 in a cyclone, which still holds good so far as the 

 observed phenomena are concerned, types of weather, 

 and local weather in relation to forecasting. All this 

 is a development of what may be termed the con- 

 ventional views in which most of us were brought 

 up; but even here the development is very consider- 

 able. The question of winds and barometric gradient 

 is happily treated, and the inclination of the wind to 

 the isobars acquires a new significance from the 

 demonstration that a wind moving in a circular path 

 may alter its direction of motion without changing 

 its velocity under the influence of a steepened gradient. 



