arriving from all parts of the world as they approach the United Kingdom
should observe at shorter intervals than six hours. As a general
instruction on this head the series of three-hourly observations may be
commenced on board vessels from America and the Pacific by the way of
Cape Horn on their passing the 20th meridian, such three-hourly
observations to be continued until the arrival of the vessels in port.
Ships by the way of the Cape of Good Hope should commence the
three-hourly series either on leaving or passing the colony, in order
that the phænomena of the tropical depression hereafter to be noticed
may be well observed.


_Northern Atlantic. Outward-bound Voyages_.--Vessels sailing to the
United States, Mexico, and the West Indies, should observe at three
hours' interval upon passing the 60th meridian. Observations 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 phænomenon, 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