PKOCEEDINGS 



OF 



THE ROYAL SOCIETY. 



" On the Relation between Tropical and Extra-tropical 

 Cyclones." By Hon. Ralph Abercromby, F.R.Met.Soc. 

 Communicated by R. H. Scott, M.A., F.R.S. Received 

 February 7, — Read February 24, 1887. Revised April, 

 1887. 



W * 



The author has long been engaged in the study of cyclones in the 

 temperate zone, as illustrated by those in Great Britain; but as doubts 

 have been expressed by many meteorologists as to the identity 

 between tropical and extra-tropical cyclones, he visited, in the year 

 1886, the observatories at Mauritius, Madras, Calcutta, Manila, Hong 

 Kong, and Tokiyo, so as not only to procure more published materials 

 for the investigation, but still more to learn from conversation with 

 those who have had great experience of tropical hurricanes, some 

 minute details of weather which were of primary importance, but 

 which could not always be extracted from existing reports. 



Though he was not fortunate enough to experience a hurricane 

 himself, still he obtained sufficient information to enable him to arrive 

 at a very definite conclusion on the matter, and now has the honour 

 of laying before the Royal Society the results of his investigations. 



He wishes to acknowledge here the assistance he has received from 

 Mr. Meldrum at Mauritius ; Mr. Pogson at Madras ; Messrs. H. F. 

 Blanford and A. Pedler at Calcutta; Padre Faura at Manila-; 

 Dr. Poberck at Hong Kong • and Messrs. Knipping and Wada at 

 Tokiyo. 



It will be convenient to sketch first the character of a British 

 cyclone ; then to detail the researches in India, the China Seas, and 

 Mauritius ; and, finally, to compare the results so as to arrive at a 

 conclusion as to the identity or otherwise of the different kinds of 

 cyclones. 



The typical shape of a British cyclone is certainly oval, the suc- 

 cessive isobars being non-concentric as in the diagram, fig. 1. The 

 longer diameter of the oval may lie in any direction relative to the 

 path of the cyclone, and often shifts during the existence of the same 

 depression ; but on the whole the tendency of the longer diameter is 

 to approximate in direction to the line of the path of the cyclone. 



VOL. XLIII. B 



