4. Some very interesting facts might result from the 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 also 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 be carefully compared
throughout a large extent of the scales, and tabulated for the purpose of
applying the requisite corrections when necessary, and one or more of
them should be compared with the standard instruments at the Royal
Society or Royal Observatory on your return home.

6. All observations which involve the comparison of minute differences
should be the mean result of at least three readings, and should be as
much as possible the province of the same individual observer.

7. In some of those singularly heavy showers which occur in crossing the
Equator, and also at the changes of the Monsoon, attempts should be made
to measure the quantity of rain that falls in a given time. A very rude
instrument, if properly placed, will answer this purpose, merely a wide
superficial basin to receive the rain, and to deliver it into a pipe,
whose diameter, compared with that of the mouth of the basin, will show
the number of inches, etc. that have fallen on an exaggerated scale.