TRANSACTIONS OF SECTION A. 799 



Hon. Ralph Abercromby and laboriously carried out by Professor Koppen 

 and Professor J. Van Bebber in their recent discussion of ' Die isobaren Typen des 

 uordatlantischen Ozeans und West-Europas.' [Hamburg, 1895.] 



Abercromby, in his ' Principles of Forecasting by means of Weather Charts,' 

 published by the Meteorological Council, classifies weather types under four heads 

 — northerly, southerly, easterly, and westerly. 



Professors Koppen and Van Bebber recognise twenty specific types of ?/ daily 

 weather. 



A comparison of these with Abercromby's shows them to be all included in 

 one or other of his four primary headings, of which they form specific sub-types. 



The investigation further shows that : 



(1) They admit of being more scientifically classified under the heads 



oceanic, K continental, L littoral, P peripheral. N northerly, and S 

 southerly. Sub-variations are denoted by suffixes, thus : , O^, 0(, 

 0„, &c. ■ 



(2) Certain groups occur preferably at each season, i.e. the seasonal type or 



tendency partly controls the formation of the y daily types. 



(3) The intensity and paths of travelling high and low pressure systems 



vary with each type and season. 



(4) Their effect in raising or lowering temperature and otherwise materially 



altering the weather is specifically shown by comparisons at such places 

 as Hamburg and Munich. 



(o) Their average duration is found to be about four days, and this figure is 

 remarkably constant on the average for all the twenty species. 



(G) There appears to be a fairly definite tendency on the part of certain types 

 to succeed other types or to recur, such recurrence in some cases ap- 

 proximating to the seasonal permanence exhibited in the tropics. 



In fine, a science of weather types is growing up by which even now the weather 

 may, with due regard to a sudden change of type, be provisionally forecasted in 

 general terms, and particularly for agricultural purposes, for ha(f n weel: or more. 



The present daily forecast in England is admirable for the purpose for which it 

 was primarily instituted, viz. storm warning. 



For agricultural purposes it is too short, while its assumption of precision in 

 the matter of rainfall for each sub-division is not always warranted by the results. 

 The author, therefore, suggests that in view of the hopefulness of the field un- 

 locked by Professors Koppen and Van Bebber, steps be taken to compare the past 

 weather maps of the British office with the types they have determined, and that a 

 supplemental forecast be presently attached to the daily forecast, giving a more 

 general forecast of conditions likely to continue for three or four days, based on the 

 ascertained presence of a certain type over Western Europe and as far over the 

 Atlantic as can be determined through the aid of arriving ship's logs. 



10. The Rainfall of the South-Western Counties of England. 

 By John Hopkinson, F.R.Met.Soc, Assoc.Inst.C.E. 



The counties here considered as South- Western are Monmouth, Hereford, Wor- 

 cester, Gloucester, Wilts, Dorset, Somerset, Devon, and Cornwall. They cover an 

 area of 11,273 square miles, which is between one-fourth and one-fifth that 

 of England, and nearly one-tenth that of the British Isles. The mean monthly 

 rainfall for the ten years 1881 to 1890 at 72 stations in these counties has been 

 calculated, and the mean annual rainfall at 113 stations, being one to the nearest 

 100 square miles in each county. Thus, for example, the annual rainfall of the 

 smallest county, Monmouth (496 square miles), is deduced from the records of five 

 stations, and that of the largest, Devon (2,586 square miles), from the records of 

 twenty-six stations. 



