Observations on a dangerous Rock at Colombo. 12] 
say, that M. Bessel does not use, or does not know how to use, 
his own tables. 
To be brief: The error of your correspondent has arisen from 
his supposing the increase or decrease of the differences to be re- 
gular, and calculating accordingly. If instead of taking a mean 
proportional part of the difference, he will find the érue diffe- 
rence, by interpolation ; for Dec. 14. 56 he will get 0,026, which 
subtracted from +0.273, gives +0247, the very sane M. Bes- 
sel has given in hisexample. If in the same way he will recal- 
culate the ‘‘ some hundreds of observations,”’ which he tells us he 
has reduced, I have no doubt it will lead to a conclusion very: 
different from that he has so rashly adopted. I will also hope 
that, calculating in this way, he will find that the tables do give 
the same corrections I have made use of. 
I am, sir, your obedient servant, 
JaMEs GRoosy. 
XXXII. Observations on the dangerous Rock usually called 
* The Drunken Sailor, lying off the Flag-Staff Point, Columbo, 
Island of Ceylon. By Licut. Col. Gzorncr Wricur*, 
Tue above rock, usually called by the English The Drunken 
Sailor, and by the Dutch De Dronke Matroos, lies in a direc- 
tion by compass about west-south-west from the Flag-staff of 
Colombo, and distant from a bold projecting rock usually named 
the Portuguese Rock, on the sea shore directly in front of the 
Flag-staff about three quarters of a mile. Its situation is in a 
most dangerous position, being exactly in the track that a ship 
would make in trying to reach the anchorage in the roads of 
Colombo during the north-east monsoon, and at which time it 
may be considered as most dangerous, from the circumstance of 
the sea not making any break upon it, -which is the case during 
the south-west monsoon, when breakers are distinctly seen at 
intervals, and which in general sufficiently mark its position: but 
even then it is not always visible, as at times only a small white 
surge scarcely discernible can be perceived to rise over it once 
in seven or eight minutes. 
Upon the summit of the rock the greatest depth of water 
which has as yet been ascertained, is about sia feet; and the 
smallest about three feet and a half, that being the usual dif- 
ference of the tides on this coast, or rather the difference of 
level in the sea caused more by strong southerly winds than by 
the tides, which at Colombo do not reach two feet. The sum- 
mit of the rock is very small, and appears to be of an oval shape, 
of about ¢wenty or thirty feet in circumference, and the sides 
* From the Transactions of the Ceylon Literary Society. 
Vol. 59. No. 286, Leb. 1822, Q of 
