1904.] Some Aspects of Modern Weather For ecasthig. 455 



WEEKLY EVEXIXG MEETIXG, 

 Friday, Febmaiy 12, 1904. 



His Grace The Duke of Northumberland, K.G. D.C.L. F.R.S., 



Presideut, in the Chair. 



W. X. Shaw, Esq., Sc.D. F.R.S. M.R.I., Secretary of the 

 Meteorological Conucil. 



Some Aspects of Moclern Weather Forecastbvj. 



[abstract.] 



After referring to the circumstances under which he was called 

 upon to deliver the Evening discourse in the absence of the Dean 

 of "Westminster, the lecturer explained that he had chosen the 

 subject, not because he regarded weather forecasting as the only, or, 

 from the scientific point of view, the most important practical branch 

 of Meteorology, but because, in a general sense, the possibility of its 

 application to forecasting — the deduction of effects from given causes 

 — was the touchstone of scientific knowledge. 



The process of modern forecasting was illustrated by the daily 

 weather charts of the period from February 1, 1904, up to the evening 

 of the 12th, which exhibited the passage over the British Isles of a 

 remarkable sequence of cyclonic depressions, reaching a climax in a 

 very deep and stormy one on the evening of the lecture. It was thus 

 pointed out that the barometric distribution and its changes were the 

 key to the situation as regards the weather, and this was supported 

 by exhibiting the sequence of weather accompanying recognised types 

 of barometric changes, as shown in the self-recording instraments at 

 the observatories in connection with the Meteorological Office. 



Some cases of difficulty in the quantitative association of rain- 

 fall or temperature changes with barometric variations were then 

 illustrated. The barometric distributions in the weather maps for 

 April 8 and April 16, 1903, were shown to be almost identical, and 

 yet the weather on the later date was 10° colder than on the earlier. 

 The observatory records for June 'I'JL, 1900, showed that a barometric 

 distiu^bance of about the fiftieth of an inch, too small to be noticed 

 on the scale of the daily charts, passed across the country from 

 Valencia to Kew, over Falmouth, in about twenty-four hours, and 

 produced at each observatory characteristic changes of temperature 

 and wind, and also in each case about a fifth of an inch of rainfall. 



Some examples of the irregularity of motion of the centres of 



