1843.] Ninth Memoir on the Law of Storms in India. 803 



About noon on the 30th, we find that the Tenasserim then in latitude 

 1 7° 24', longitude 91° 28', had had the weather severe enough from the N. 

 Westward to be lying to from 2 a. m., and that the wind then shifted 

 to a gale from the S. S. W., which kept her under storm stay sails for 

 the rest of the 24 hours. This shift, again, is what should occur, if we 

 suppose, as before, a vortex forming to the N. E. of her track on the 

 preceding days, and then suddenly moving on to the W. N. W., its 

 centre passing near to the Northward of her position, for such condi- 

 tions could give exactly a shift from N. W. to S. S. W. I have 

 marked two small circles on the charts to guide the eye in considering 

 this supposition, which I merely make in the absence of better data to 

 regulate our views. I need not again repeat that storms must being 

 somewhere and somehow, and the faintest light thrown on the phe- 

 nomenon of their beginnings is of importance.* 



We may perhaps assume this place close to the Tenasserim at Noon 

 on the 30th, to have been the centre of the nascent storm on that day, 

 and that while the vessel was drifting to the Northward with a S. S. 

 Westerly gale, the storm was passing slowly to the Westward. This 

 would gradually bring the wind for her to the S. S. E. as she got upon 

 the N. E. quadrant of the storm, and so she, in effect, had it by 6 a m. 

 the morning of the 1st October, when she bore away to the N. W. by 

 N., and running always on the N. E. quadrants of the two storms, 

 had heavy S. Easterly breezes with a heavy Southerly sea to the 

 Sand-heads. I regret much that this vessel's log is in some respects 

 imperfect, and above all, that though a Government Steamer, she 

 had apparently neither Barometer nor Sympiesometer on board ! for 

 no observations of either are given. Observations of good instruments 

 in her position would have been invaluable. 



We should not forget to take into account in weighing all this, that 

 Cape Negrais is a notorious neighbourhood for variable winds and 

 shifting storms and gales, and that the Tenasserim's weather may 

 have been mere local variations of the monsoon, and that thus the 



* I have supposed here and in former papers a circular storm, forming and then 

 moving forward, i. e. remaining stationary, or nearly so, at first. We do not know 

 if the dust-whirlwinds, so common in hot climates, and water spouts are generated by 

 the same causes, and subject to the same laws, but both these phenomena certainly 

 do what I have here supposed the storm (or storms) to do, that is, many of them are sta- 

 tionary or nearly so while forming, and then to use Bruce's words " stalk forward." 



