179 



On the Tides at Madras. 



[April 



and consequently of the inestimable value of this instrument to 

 every commander of a ship, and more especially to those whose 

 destination is India. 



I am, Sir, your obedient Servant. 



MERCURIUS. 



V. — Memorandi'm on the Tides at Madras, November 1821* 

 Bij Lieut. Col. DcHavilland of the Madras Engineers. 



The results of the observations made on the tides at Madras by 

 the menns of a Tide Gauge near the north east angle of the 

 glacis of the Fort from the 31st May to the 10th October 1821 

 inclusive, were as follows. That high water on the full and change 

 of the Moon, was at 8h 58 or 9h. That on those days the difference 

 of elevation of the surface of the sea at high and low water, was 2 

 feet 7| inches ; that on the 4th days of the Moon s age, and the 

 coriesponding days after the full, this difference was 3 feet 5\ 

 inches the maximum and that the 2d days after the 1st and 3d 

 quarters, it was reduced to 1 foot 7J inches the minimum. It was 

 also observed, that the daily decrease was greatesty on and imme- 

 diately before the 1st and 3d quarters, and the increase leasts im- 

 mediately after. It was likewise remarked, that the average level 

 of the sea at mid-tide, or between high and low water, varied with 

 the Phases of the Moon. That it appeared highest on the 3d days 

 of the Moon's age, and the corresponding days after the full, and 

 lowest on the 2d days after the 1st and 3d quarters — and the dif- 

 ference was observed to be about 1 foot 4 inches ; but it is proba- 

 ble that this being so great, was owing to some anomaly, in the 

 observations made on the 3d days of the Moon's age, and those 

 corresponding after the full, and that in point of fact, it was not 

 more than 1 foot. The following table contains the particular ot 

 these results. The retardation of the tides from day to day was 

 considerably less for the first four or five days after full, and change 

 than at any other time ; it was then about 30 per diem. 



