in a Voyage from Sierra Leone to New York, 429 
The voyage from Ascension to Bahia commenced in the 
continuation of the same drift-current from the S.E. in which 
the latter part of the passage to Ascension was performed ; but 
on the 13th of July, the Pheasant appears to have re-entered 
the southern border of the Equatorial current, in the longitude 
of 221 W., and latitude of 10} S. The evidence of many 
voyages in different years, the journals of which have been 
submitted to Major Rennell’s examination, have led him to 
the conclusion, that it is the ordinary course of that stream, 
to divide into two branches about the twenty-third degree of 
west longitude: the northern portion flowing in a north-west 
direction, and diffusing its waters in the basin of the Atlantic ; 
and the southern, which is the largest portion, proceeding in 
a direction to the southward of west, until it reaches the coast 
Prince’s Island and at St. Thomas. It may be a sufficient explanation to re- 
mark, that Annabonaisalways surrounded by the Equatorial current ; Prince’s 
Island always by the Guinea current; and that the position of St. Thomas 
is intermediate, and its climate is occasionally influenced by both. In tro- 
pical climates a very few degrees of temperature constitute an essentia. 
difference in the feelings of the natives, and in the health of Europeans. 
The point of deposition varied over the differently-heated surfaces of 
water, in correspondence with the difference in the temperature of the air ; 
so that, although the quantity of moisture was diminished in the colder air 
over the Equatorial current, the proportion of the quantity to that which 
would have been required for repletion, was as nearly as possible the same 
as over the Guinea current, being on the average 84°°5 parts in 100° in 
both instances. The air, therefore, was equally moist over the Equatorial 
as over the Guinea current, although in the one case the weight of vapour 
ina cubic foot (derived from the averages) was 10 grains, and in the other 
7:93 grains only. The cold air incumbent on the Equatorial stream, being 
borne by the south wind over the surface of the Guinea current, caused 
the deposition, which generally obscured the horizon to the north of St. 
Thomas, during the pendulum observations; and which fell, as we under- 
stood, in heavy rain in the offing. The quantity of vapour in the atmosphere 
over the island being less than that over the nearly surrounding water of 
the Guinea current (an effect of the high land of which the island consists), 
no deposition took place on the island itself. The hygrometer indicated 
the temperature of its superincumbent vapour to be between the extremes 
of 71° and 74°5, observed three times a-day between the 26th of May and 
the 12th of June. The range in the Gulf of Guinea was from 76° to 80°. 
It is worthy of notice to what little distance the colder air, impelled by 
the constant south wind, attained over the Guinea current before it be- 
came itself heated by the condensation of the vapour of higher consti- 
tuent temperature. ‘The great bodies of the air and of the vapour over the 
respective currents, though so dissimilar in temperature, were as little af- 
fected by their contiguity, as the surface waters of the currents themselves. 
By their mutual and opposite action, the air in condensing and thus reducing 
the temperature of the vapour, and the heat liberated in the condensation 
of the vapour in raising that of the air, the mixture speedily destroyed the 
differences ; and the eflects of the contiguity were thus limited to a very 
few iniles within the border of either stream, 
of 
