Page:Narrative of a Voyage around the World - 1843.djvu/35

 Rh There are, however, some occasional observations which cannot fail of being extensively useful in future investigations. 1. During the approach of the periodic changes of wind and weather ; in which case the hygrometer also should find a place in the journal.

2. The mean temperature of the sea at the equator, and under a vertical sun. These observations should be repeated whenever the ship is in either of those situations, as well in the Atlantic as in the Pacific; they should be made far away from the influence of the land, and at certain constant depths, suppose fifty and ten fathoms, and at the surface, and the latter ought to be again observed at the corresponding hour of the night.

3. A collection of good observations systematically continued, for the purpose of connecting the isothermal lines of the globe, and made as above at certain uniform depths.

4. Some very interesting facts might result from a comparison of the direct heat of the solar rays in high and low latitudes. The two thermometers for this purpose should be precisely similar in every respect; the ball of the one should be covered with white kerseymere, and of the other with black kerseymere, and they should be suspended far out of the reach of any reflected heat from the ship, and always at the same elevation above the surface of the water; the observations should be made out of sight of land, in a variety of latitudes, and at different hours of the day, and every pains taken to render them all strictly similar and comparative.

5. All your meteorologic instruments should early in the voyage be carefully compared throughout a large extent of the scales, and tabulated, for the purpose of