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page 111 ---meteorology----scientific instruments and measurements---

Great and glorious are the impressions which the stranger here receives of the power and peace of the elements; but unused to the torrid zone, he feels a disagreeable sensation from the moisture and coolness of the morning and evening, and the oppressive heat of the noon. The whole crew, therefore, began to complain, in this latitude, of headache and cholic; and only artificial means, such as tartar and rhubarb, could prevent disease, in a climate where the rays of the sun fall perpendicular. At length we came, though slowly, out of this region of sultry and wearisome calm, because the wind which blew after the thunderstorms at noon, always carried the ship a little forward; by degrees, too, a faint south wind arose, varying from S.E. to S.W., and diminished the temperature, in the morning, at 7 o'clock, in the air, to 20.75° R., in the water to 22°; at noon, in the air, to 21.50° R., in the water to 22°; in the evening , at half-past seven, in the air, to 21.25°. When we had reached longitude 21° 21' west of Paris, and 5° 28' N. latitude, the wind began to blow more steadily from the S., and fixing in S.E. and S.S.E., formed the constant wind, which blowing regularly, accompanied us through these latitudes.

page 112 ----astronomical puzzle----trade winds----

We still saw for a moment the polar star, a few degrees above the horizon, which is here generally clouded; on the other hand the Southern Cross, and the other constellations of the southern hemisphere, were likewise low.

From this, as well as from the nautical observations, we knew that the equator was still some degrees to the south of us; but the uniformity and harmony in the phenomena of nature, which we had observed between the 10th and 5th parallels of latitude, seemed again to decrease, and thus to prove that the line of culmination of those phenomena is not in the equator, but several degrees to the north of it. We must leave it to the natural philosopher and the astronomer to decide whether this, perhaps, may arise partly from the heavier mass of continents, from the nutation, or from the revolution of the earth round the sun, &c. It is remarkable in this respect, that the N.E. and S.E. trade winds do not cease at an equal distance from the equator.

The trade winds, which are supposed to arise from the rotation of the earth round its axis, and from the current of colder air towards the warmer region between the tropics, regularly vary in their extent, according to the position of the sun. When it is in the southern torrid zone, the N.E. wind always blows towards the equator; when it is in the northern torrid zone, the S.E. wind blows nearer to, nay, even beyond it. Between the two trade winds, there are sometimes faint winds, especially from S. and S.S.W. which are more limited by the first, sometimes on the north and sometimes on the south.