near the northern entrance of the Straits Malacca. 9 ' 
^ This phenomenon may be accounted for in two ways ; either 
by supposing that there actually was a change in the force and 
direction of the wind incident to the ripples alone, or else that 
there was a local current which belonged to them, and not to 
the contiguous sea. It seems less difficult to conceive the last 
supposition ; which we are farther led to adopt, from having dis- 
covered, by means of chronometers, and good meridian alti- 
tudes of the sun and stars, that the ship, during the day, had 
actually been set to the north-west by west, (N. 56 W.) at 
the rate of nearly one mile an hour, strictly 0.79 of a mile 
A reference to the figure, Plate I. Fig. 1., will shew how a current 
in that direction would account for the facts. Let the shaded 
space FG be the ripple, AB the ship’s course (west south-west,) 
before entering it, and H the direction of the wind. On enter- 
ing the ripple at B, suppose the influence of the current to 
commence, then the ship’s true course, or the path she actually 
takes, will be the diagonal of the parallelogram of which the 
ship’s apparent course and rate of sailing furnish one side, say 
W. S. W. 1.88 (BC), and the temporary current N. W. b. W. 
6.84} (CD) another ; then the true course, while in the ripple, 
will be W. N. W. 8, (BD) DE, the course after quitting 
it, as before, W. S. W. Now, it is clear, that if a ship sail- 
ing in the direction AB with the wind H, is suddenly car- 
ried out of her course in the direction BD, an apparent al- 
teration in the wind must take place. The degree of this 
change will depend upon the relative velocities of the wind 
and the current. If the velocity of the wind in both cases 
could be exactly determined, together with the change in the 
angle of its direction, a means of ascertaining the force and di- 
rection of the current would be aflbrded. The experiment, in- 
deed, would require much care and nicety ; but as the result 
might lead to the most important conclusions in the very ob- 
scure subject of currents, it is greatly to be desired that naviga- 
tors would permit no opportunity to pass, without endeavouring 
to furnish more accurate observations. 
* The accurate Captain Horsbprgh, in describing these ripples, says, that they 
are not always accompanied by currents. 
•|* These numbers, 1.88, &c. serve merely to express the supposed of the vc* 
iocities of the two forces acting on the ship, and that of the resultant or true course. 
