1841.] Fourth Memoir on the Law of Storms in India. 903 



We have now to examine the construction of the Chart, and the 

 evidence there is for the two storms as there laid down. 



Taking first the Loiidon Thetis^ as the vessel which was farthest 

 to the northward, we find her on the 21st September with the wind 

 at NW. with ugly weather, and the Simpiesometer warning her by 

 its oscillations, of had weather for the whole previous 24 hours ; being 

 moreover 0.50 to 0.80 below the Barometer!* The Calcutta Thetis had 

 thick cloudy weather, with a smart breeze at NNW. ; her Barometer 

 sinking to 29. 70 



At noon on the 22nd, the London Thetis, with the sea rising from 

 the NE. and Northward, the wind increasing from NNW. the weather 

 threatening, and the glasses still warning, very properly hove to under 

 trysails. We may take the storm to have fairly begun with her now, 

 and I have thus laid down its centre as bearing from her about 1 30 

 miles to the ENE., which, assuming it to be a circular storm, would 

 give it a diameter of 260 miles. 



The Calcutta Thetis at the same time has the wind a strong breeze 

 at W. by S. to which point her NNW. breeze had gradually veered ; her 

 Barometer had fallen to 29.56, with threatening weather and a head 

 sea, the ship always running to the NE. from 6 to 5 knots an 

 hour. If we look at the circle of the London Thetis storm, we see 

 that this could not be the same ; for if we extended it to here, 

 it would give us the wind at about NW. by W. instead of W. by S. while 

 it is to be particularly noted, that the changes of wind which the Calcutta 

 Thetis has from 7 p. m. of 21st to 4 a. m. and noon of the 22nd, are 

 exactly such as should occur from a ship, and a circular storm running 

 on the tracks which I have laid down : the ship in fact chasing the 

 storm ! Thus it will be seen that at 4 a. m. when it was N W. the 

 first circle on the track of this storm makes it so, and this track must 

 be the right one, because the wind being W by S. at noon, clearly shews, 

 that the ship had passed to the Eastward of the meridian of the centre 

 at that time, i. e. the centre was bearing N by W. from her if it was a cir- 

 cle. I do not fail to observe, that by this track she is placed within a 

 much shorter distance of the centre at this time than afterwards 

 on the 22nd at midnight, and during the 23rd, when the greatest fjill 



* A very beautiful instance of liie importance of this invaluable instrument. 



