There are, however, portions of the surface of our planet, and probably also phaenomena that occur in its atmosphere, which require still closer attention than the eight daily readings. One such portion would appear to exist off the western coast of Africa, and we recommend the adoption of _hourly_ readings while sailing to the westward of this junction of aqueous and terrestrial surface; more attention will be directed to this point as we proceed. There are also phaenomena the localities of which may be undetermined, and the times of their occurrence unknown, but so important a relation do they bear to the subject of our inquiries, that they demand the closest attention. They will be more particularly described under the head of accumulations of pressure preceding and succeeding storms, and minute directions given for the hourly observations of the necessary instruments. In the mean time we may here remark that hourly observations under the circumstances above alluded to are the more important when we consider that the barometer, the instrument employed in observing these moving atmospheric masses, is itself in motion. The ship may meet the accumulation of pressure and sail through it transversely; or she may sail along it, the course of the vessel being parallel to the line marking the highest pressure, the ridge or crest of the wave; or the ship may make any angle with this line: but whatever the circumstances may be under which she passes through or along with such an accumulation of pressure, it should ever be borne in mind that her position on the earth's surface is scarcely ever the same at any one observation as it was at the preceding, the barometer in the interval has changed _its_ position as well as the line of maximum pressure, the rate of progress of which it is desirable to observe. It will, therefore, be at once apparent that in order to obtain the most accurate data on this head hourly observations are indispensable. To these readings should of course be appended the places of the ship from hour to hour, especially if she alter her course much. There is another point to which we wish to call attention in immediate connexion with hourly readings--it is the observation of the instruments on the days fixed for that purpose: they were originally suggested by Sir John Herschel, whose directions should be strictly attended to: they are as follows:--