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 attention to their connexion, our great object here will be to endeavour to mark out such a line of observation as appears most capable of throwing light, not only on the most important desiderata as connected with storms, but also their connexion or non-connexion with atmospheric waves. We shall accordingly arrange this portion of the instructions under the following heads:--_Desiderata_; _Localities_; _Margins_; _Preceding and Succeeding Accumulations of Pressure._