ecise
boundary where the three-hourly series should commence; the 90th
meridian is recommended for the boundary as regards South America, and
from this a judgment may be formed as to where the three-hourly
observations should commence in reference to North America.

In the previous sketch of the localities for the more important
observations, it will be seen that within the tropics there are three
which demand the greatest regard.

I. The Archipelago between the two Americas, more particularly comprised
within the 40th and 120th meridians west longitude, and the equator and
the 40th degree of north latitude. As a general principle we should say
that vessels within this area should observe the barometer every three
hours. Its eastern portion includes the lower branches of the storm
paths, and on this account is peculiarly interesting, especially in a
barometric point of view.

II. _The Northern portion of the African Continent, including the Sahara
or Great Desert._--This vast radiating surface must exert considerable
influence on the waters on each side northern Africa. Vessels sailing
within the area comprised between 40 deg. west and 70 deg. east, and the equator
and the 40th parallel, should also make observations at intervals of
three hours.

III. _The great Eastern Archipelago._--This presents a somewhat similar
character to the western; like that, it is the region of terrific
hurricanes, and it becomes a most interesting object to determine its
barometric phaenomena; the three-hourly system of observation may
therefore be resorted to within an area comprised between the 70th and
140th meridians, and the equator and the 40th degree of north latitude.

The southern hemisphere also presents three important localities, the
prolongations of the three tropical areas. It is unnecessary to enlarge
upon these, as ample instructions have been already given. We may,
however, remark, with regard to Australia, that three-hourly
observations should be made within the area comprised between the 100th
and 190th meridians east, and the equator and the 50th parallel south,
and hourly ones in the immediate neighbourhood of all its coasts.

IV.--STORMS, HURRICANES, AND TYPHOONS.

The solution of the question--How far and in what manner are storms
connected with atmospheric waves?--must be extremely interesting to
every one engaged in either the naval or merchant service. As we have in
the former chapters directed attentio