ScHAW. — Interaction of Cyclones. 567 



instance of a hard bituminous coal giving off sulphuretted 

 hydrogen at the temperature of the air." One or two Euro- 

 pean coals, all more or less hydrous, give off small quantities 

 when boiled in water, but it is very difficult to say whether 

 these are parallel instances. Water may have power to de- 

 compose many of those complex organic sulphui" compounds 

 whose existence in coal is almost certain, but of whose actual 

 properties we are still entirely ignorant. 



Art. LVI. — On the InteractioJi of Cyclones xipon one another. 



By Major-General Schaw, C.B., E.E. 

 [Read before the Wellington Philosophical Society, 20th September, 1898.1 



Plates LIII. and LIV, 



Last year, in a paper read before this Society on the 14th 

 July, I gave the history of two storms — the one antarctic, the 

 other tropical — which met in the region of Cook Strait on the 

 30th January, 1897, and which seemed to repel one another, 

 the antarctic storm being diverted southwards and the tropical 

 storm northwards. This year — in June last — a somewhat 

 similar meeting between an antarctic and a tropical storm 

 took place ; but, instead of repelling one another, the antarc- 

 tic storm blended with and absorbed the other, in the same 

 way that one antarctic storm often blends with another which 

 has been delayed, and which it overtakes. 



The two storms to which I drew attention last year were 

 moving in nearly opposite directions when they met and re- 

 pelled each other ; and I suggested that probably there was 

 a limiting angle between the directions of the tracks of two 

 storms w^hose paths met inside of which angle they coalesce, 

 and outside of which they are diverted. This supposition 

 appears to be supported by the behaviour of the two storms 

 which coalesced on this occasion, and the limiting angle seems 

 to be about 120°. 



The circumstances on this occasion were as follows : On 

 the 23rd June a tropical cyclone of moderate intensity, and 

 moving slowly from north-west to south-east, struck the 

 northern extremity of New Zealand. The force of the wind 

 was sufficient to interrupt telegraphic communication as far 



* As the gas was evolved during the act of pulverisation, local in- 

 crease of temperature due to mechanical action may have to be taken 

 into account. 



