332 Capt. Sabine’s Remarks on the Method of investigating 
acid, containing a little naphthaline, and some free sulphuric 
acid; whilst the lighter substance is a solution of the dry acid 
in naphthaline; the water present in the oil of vitriol originally 
used being sufficient to cause a separation of a part, but not 
of the whole. 
(To be continued.] 
LIT. Hydrographical Notices :—Remarks on the Method of in- 
vestigating the Direction and Force of theCurrents of theOcean; 
Presence of the Water of the Gulf-Stream on the Coasts of Europe 
in January 1822; Summary of the Currents experienced by 
His Majesty's Ship Pheasant, in a Voyage from Sierra Leone 
to Bahia, and thence to New York; Stream of the River 
Amazons crossed, three hundred Miles from the Mouth of the 
River. By Capt. Enwarp Sasint, &. A. FR. § LS. §c.* 
PREVIOUSLY to my leaving England in 1821, I had had 
the great advantage of much conversation with Major 
Rennell, on the subject of the currents in the northern and 
southern Atlantic Oceans, and of having my attention direct- 
ed by him to those points in particular, concerning their ve- 
locity, limits, and temperature, on which further inquiries 
might conduce to the advancement of hydrographical know- 
ledge. 
The method of ascertaining the existence, direction and ye- 
locity of a current, where land is not in sight, and a ship can- 
not be rendered stationary by anchorage, is to compare her 
position at intervals of sufficient length (generally of 24 hours) 
by observation and by reckoning. By the former is learnt 
her real change of geographical position in the interval; by the 
latter, the course and distance that she has gone through the 
water; should the position by the reckoning not agree with 
the position by the observation, the difference (presuming both 
to be correct) is the indication and measure of current. 
To determine a ship’s position from day to day by observa- 
tion, or rather, her relative position on one day to the pre- 
ceding, has become, since the introduction of chronometers, a 
matter of very simple accomplishment, and capable of much 
precision. It is far otherwise with the reckoning, however, 
when more is sought by it than such a rough approximation 
as may serve the ordinary purposes of navigation: it must, in 
fact, require the most assiduous and unremitting attention, as 
well as considerable nautical experience and judgement, to 
* From Captain Sabine’s newly-published Account of his Experiments to 
determine the Figure of the Earth. 
estimate 
