1839] 



and Set of the Tides at Madras. 



141 



Avould be above water) so as to admit a slight rod to pass freely; this 

 rod being attached to a light hollow copper box — which would float on 

 the surface of the water within the cylinder, — the variation in height of 

 its upper end, would indicate to an observer on shore the variation of the 

 level of the sea, &c. This 'apparatus was got ready and one attempt 

 made to drive it, but the want of proper anchors, &c. produced a failure, 

 and up to the present time I have not been able to procure the needful 

 to make a second attempt. Under these circumstances I may be permit- 

 ted to offer observations, which, although not nearly approaching to that 

 degree of accuracy which might be desired, still will supply usefully 

 approximate results. The observations to which I allude consist in de- 

 ducing from the observed depressions of the sea and buoys, the height 

 of the telescope above the level of the sea ; thus, on the 3d of November 

 at 6 A. M., I observed the line of floatation of the buoy No. 1 to be de- 

 pressed 2° 5' below the horizon of the sea, hence 



Depression below the sea 2 5 0 



Dip 5 30 



Depression below the horizon 2 10 30 nat. sin. = ,03793 



distance of object — X 828 feet 



height of telescope above the sea— 31.43 feet 



