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cation is the effect of the evaporation of rain in cooling the air, and reducing the dynamical warming of descending air. With so many factors acting, every front has its own special features.

An interesting point which was novel when the paper was first written. though it is now a commonplace of frontal analysis, is the formation of the " back-bent occlusion." T h e memoir should be read by all w h o wish to understand modern synoptic meteorology. Only those who have done this type of research realise the large amount of time which it occupies. Dr. Bjerknes had a considerable amount of routine instructional work when in London, and his researches often occupied him late in the evening, ar even on Saturday afternoons. Large numbers of records were examined in addition to those used in the memoir.

The author's command of the English language, and the clearness with which he expresses his ideas, will need no recommendation to those familiar with his-earlier work.

C. K. M. D.

Atlas pluviom&tric de Cataltmya. By JOAQUIM FEBREK. Membries Patxot Volum I. Barcelona, 1930. 4". Pp. 523, including 53 pp. of maps.

This *' Rainfall Atlas of Catalonia " was awarded first prize in t h e Patxot competition of 1925, which was instituted by M. Raphael Patxot i Jubert in order to stimulate research in the physical sciences and i n mathematics, especially in Catalonia.

The publication includes maps of Catalonia (the northeast of Spain, extending for about IOO miles round Barcelona), on the scale of 22 miles to I inch, showing the following information :-(a) the positions of the 306 rainfall stations, (b) the average rainfall of each month, (c) the average rainfall of each of the four seasons, (d) the average annual rainfall, (e) the total rainfall during the dry year iyxr, (fl the total rain- fall during the wet year 1921, (g) the average monthly rainfall a t 25 well-distributed stations, (h) the average rainfall of each month as a percentage of the annual average, (0 the average number of days with measurable precipitation in each month, ( j ) the average number of days on which the precipitation took the form of snow or of rain and snow.

Details are also given of the monthly rainfall (in mm.), the number of days with rain and the number of days with snow a t each of the 306 stations from the commencement of the record until 1925. The tables occupy 350 pages. Although the information is not marshalled in the most concise form the resulting production is perhaps more pleasing than would have been the case if that had been done.

The general practice adopted in Catalonia in connection with climato- logical statistics, of using the seasonal year December to November is adhered to. Th-us in the tables and maps December is taken as the initial month. Another departure from the routine adopted in the British Isles is that the rainfall maps are drawn without reference to the con- figuration.

The map of the average annual rainfall shows n variation of from rather less than 350 mm. (14 in.) to the west of Barcelona to over 1,400 mm. (55 in.) in the mountainous area in the estreme north-west. In the driest year (19x2) about one-half of Catalonia received less than 3jo mm. (14 in.) and a large area less than 150 rnm. (6 in.). T h e variations in the distribution of the average monthly rainfall throughout the year in Catalonia, as shown by the maps and diagrams, are not typical of the Mediterranean. Along the coast autumn rains predominate. In the southern half of the country least rain falls in the three summer months, notably in Tune and August. Further south the summers are, of course, practically rainless. In the southern half of Catalonia the summer rainfall is 40 to 80 mrn. (1.6 to 3.2 in.). The fall of the three winter months only exceeds that of the sunimcr by small nmounts. In

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the north, least rain falls in the winter. This comparatively low winter rainfall is associated with the relatively high pressure in these regions.

During each month of the year appreciable areas record rain on the average on only three days, suggesting an abundance of sunshine for which, of course, the Mediterranean region is famous.

M. Joaquim Febrer, Head of the Climatological Section of the Meteorological Service of Catalonia, and M. Raphael Patxot i Jubert, are to be congratulated on making available to the general public this standard book of reference.

J. G.

fleroriautical dleteorology. By WILLIS RAY GREGG. New York (Ronald Press Company), 1930. Second and enlarged edition. Svo. Pp. xyi+405, 126 illus. $+:so.

During the last ten years it has been realised more and more by all connected with aeronautics that a knowledge of meteorology is essential to progress. The aeronautical engineer requires information regarding changes of density, pressure and temperature with height. The promoter of air routes requires data relating t o wind and weather to plan and guarantee schedules of operation. The pilot must have knowledge of the main characteristics of depressions and anticyclones, cloud formation, diurnal and seasonal changes of wind speed and direction, and the characteristics and formation of squalls, thunderstorms and fog, in order to interpret locally the more general forecasts received for a wider area.

The author seeks to meet these requirements in this revised edition and he has secured the collaboration of several meteorologists in the service of the U.S. Weather Bureau in various sections of the work. Much of the earlier edition has been rewritten and rearranged, while a considerable amount of new information has been added. The book is not intended so much for the professional meteorologist as to give the detailed information most needed by the airman, and enough general meteorology is given to provide a groundwork for the better understanding of atmospheric processes and the conditions directly related to aeronautics.

In the general meteorological section of the book there are chapters dealing among other subjects with winds, fog, clouds, thunderstorms, " ceiling " and visibility, instruments and methods of observation. Throughout this part the causes of the various phenomena are carefully explained and their possible danger to aircraft. The section on fore- casting contains a brief description of the Norwegian methods of air- mass analysis, but the enthusiasm possessed by the author for this method of forecasting appears to be rather faint and empirical rules given by Bowie, as the result of experience, seem to be favoured more.

Three chapters of the book which will have a wide appeal, partly because so much scattered information is collected for the first time and also on account of the valuable views expressed, are those dealing with airship meteorology, North Atlantic and Arctic meteorology and ice formation on aircraft. The section on airship meteorology, written by Lieut. F. W. Reichelderfer, U.S.N., Aerological Office, U.S.S. Los Angeles, contains an admirable analysis of the effects of wind prwsure, wind accelerations, changes of air temperature and humidity on the operation of an airship, and the dangers resulting from violent changes in these and other elements. The dangers and difficulties involved in a flight across the northern Atlantic between America and the British Isles are exemplified in tables showing the number of days with excellent, good, fair or poor wind conditions. In all but one notable case days and even weeks of waiting were often necessary for even moderately favourable conditions, and even then fogs and stormy weather were encountered on some part of the flight. The author considers that when winds assist it is doubtful if ten days occur each year when other condi-