472 Mr. H. F. Blanford on the Origin of a Cyclone, [June 17, 

 and that 



These results are then reduced into the following form : — 



P=p { _2^+(l-/3y-ya-«/3)X 2 +2 a /3 r % -«W ^) . 



where a, /3, y are written for 1 — — „, 1— 1 — ^- respectively. 



In the last clause of the paper it is pointed out that Poinsot's "rolling 

 and sliding cone " is a particular case of Professor Sylvester's " correlated 

 and contrarelated bodies." 



II. "On the Origin of a Cyclone." By Henry F. Blanford, 

 E.G.S., Meteorological Reporter to the Government of Bengal. 

 Communicated by Dr. T. Thomson. Received May 21, 1869. 



It has long been an object to the completion of our knowledge of vor- 

 tical storms to trace out their early history, and to show, by the compari- 

 son of a sufficient number of local observations, by what wind-currents the 

 vortex is generated in each storm-region, and by what agency these cur- 

 rents are directed to the spot at which the storm originates. 



With this object in view, I endeavoured, immediately after the great 

 Calcutta storm of the 1st of November 1867, to obtain, through the as- 

 sistance of Captain Howe (then officiating as Master Attendant of the 

 Port), the logs of as many ships as possible that had been in the Bay of 

 Bengal or anywhere to the north of the Equator during any part of the 

 last week of October. A similar application was made to the Meteorolo- 

 gical Department of the Board of Trade and readily granted. The me- 

 teorological stations recently established in Bengal, and the observatories 

 of Calcutta and Madras, contributed a number of observations, for the 

 most part fairly trustworthy ; and I was thus placed in possession of data 

 which, although far from sufficient to the complete solution of the pro- 

 blem for the storm in question, have at least enabled me to elucidate its 

 origin to a greater extent than has been accomplished, as far as I am aware, 

 for any previous storm in these seas or elsewhere. 



The following Tables give the noon barometric pressures at several sta- 

 tions in Bengal * and on the shores of the bay, and those of a few ships 



* These are calculated from the observations at 10 a.m. and 4 p.m., but so regular is 



