ons at this
interval, on board vessels navigating the Gulf of Mexico and the
Caribbean Sea, will be particularly valuable in determining the extent
of oscillation as influenced by the masses of land and water in this
portion of the torrid zone, as compared with the oscillation noticed off
the western coast of Africa, hereafter to be referred to.

_Southern Atlantic. Outward and homeward bound_.--Without doubt the most
interesting phaenomenon, and one that lies at the root of the great
atmospheric movements, especially those proceeding northwards in the
northern hemisphere and southwards in the southern, is the equatorial
depression first noticed by Von Humboldt and confirmed by many observers
since. We shall find the general expression of this most important
meteorological fact in the Report of the Committee of Physics and
Meteorology, appointed by the Royal Society in 1840, as follows: "The
barometer, at the level of the sea, does not indicate a mean atmospheric
pressure of equal amount in all parts of the earth; but, on the
contrary, the equatorial pressure is uniformly less in its mean amount
than at and beyond the tropics." Vessels that are outward bound should,
upon passing 40 deg. north latitude, commence the series of three-hourly
observations, with an especial reference to the equatorial depression.
These three-hourly observations should be continued until the latitude
of 40 deg. south has been passed: the whole series will then include the
minimum of the depression and the two maxima or apices forming its
boundaries. (See Daniell's 'Meteorological Essays,' 3rd edition.) In
passages across the equator, should the ships be delayed by calms,
opportunities should be embraced for observing this depression with
greater precision by means of _hourly_ readings; and these readings will
not only be valuable as respects the depression here spoken of, but will
go far to indicate the character of any disturbance that may arise, and
point out, as nearly as such observations will allow, the precise time
when such disturbance produced its effects in the neighbourhood of the
ships. In point of fact they will clearly illustrate the diversion of
the tendency to rise, spoken of in the Report before alluded to, as
resulting in ascending columns and sheets, between which wind flaws,
capricious in their direction and intensity, and often amounting to
sharp squalls, mark out the course of their feeders and the indraft of
cooler air