428 Capt. Sabine’s Summary of the Currents experienced 
able phenomenon of parallel streams, in contact with each 
other, flowing with great velocity, in opposite directions, and 
having a difference of temperature amounting to 10 and 12 
degrees. ‘Their courses continue thus parallel to each other 
and to the Jand for above a thousand miles; and according as 
a vessel, wishing to proceed along the coast in either direc- 
tion, is placed in one or the other current, will her progress 
be aided from forty to fifty miles a-day, or retarded to the same 
amount: the practical advantage, therefore, derivable from 
the difference of temperature, in enabling vessels to discrimi- 
nate at all times in which current they are situated, is as great 
as it is obvious*. 
The 
* The occasional advance of the cold water of the Equatorial current to 
the island of St. Thomas, may assist in explaining an apparent peculiarity in 
the climate of that island, when compared with the climate of the coast of 
Western Africa generally. At all the British possessions, from the Gambia in 
13° north latitude to the forts on the Gold Coast, June, July and August, are 
accounted the unhealthy months; whilst at St. Thomas, on the contrary, 
they are the most healthy in the year to Europeans, although they are not 
so to the Negroes, who suffer much from colds and rheumatism during their 
continuance. It has been seen, that the water of the Equatorial current is from 
10 to 12 degrees colder than that of the Gulf of Guinea,and that its northern 
border, which at other seasons passes the meridian of St. Thomas at a di- 
stance from 120 to 180 miles south of its southern extremity, was found in 
June in contact, or very nearly so, with the island itself; and it is not im- 
probable, from a consideration of the causes which occasion its advance 
towards the equator when the sun is in the northern signs, that in July it 
may extend so far, as even to include the whole island within its limits. 
The temperature of the air is known to be immediately dependent on 
that of the surface-water of the sea, and to be influenced nearly to the full 
extent of any alteration that may take place therein. In crossing the Gulf 
of Guinea from Cape Formosa to St.Thomas, the air over the surface of the 
Guinea current, observed in the shade and to windward, at sunrise, noon, 
and sunset, averaged 81°-5, the extremes being 79° and 83°°5; whilst in 
the passage from the river Gaboon to Ascension, over the Equatorial cur- 
rent, the air averaged only 74%, the extremes being from 73° 5 to 74°°5; a 
part of the passage being, moreover, on the very edge of the two currents, 
aud within sight of St. Thomas. The vicinity of the Equatorial current, there- 
fore, when the sun is in the northern signs, cannot fail materially to in- 
fluence the temperature of the island (particularly as the wind is always 
from the south), and thus to affect its climate. Situated on the equator, 
St. Thomas has naturally two cold seasons, or winters, in the year, the sun 
being equally distant in June and in December; but in June, July and 
August, is superadded the influence of the surface water of the ocean se- 
veral degrees colder than in November, December, and January; rendering 
the months of June, July and August, pre-eminently the winter of St. 
Thomas ; in which the natives complain of colds and rheumatism, and the 
health of Europeans is less affected than at other seasons, because the 
climate is then less dissimilar than usual to their own. 
The comparative unhealthiness of Prince’s Island to St. Thomas, and of 
both to Annabona, as the residence of Europeans, has been frequently and 
particularly noticed by Portuguese authorities, and is universally recognized at 
Prince’s 
