There can be no question that the greatest amount of information, the accuracy of the data supplied, and in fact every meteorological element necessary to increase our knowledge of atmospheric waves, may be best obtained by an uninterrupted series of _hourly_ observations made on board vessels from their leaving England until their safe arrival again at the close of their respective voyages; but from a variety of circumstances--the nature of the service in which the vessels may be employed, particular states of the weather, &c.--such a course of unremitting labour cannot be expected; it is therefore necessary to fix on some stated hours at which the instruments before particularized should be regularly observed throughout the voyage, and their indications faithfully recorded. The hours of 3 A.M., 9 A.M., 3 P.M., and 9 P.M., are now so generally known as _meteorological hours_, that nothing should justify a departure from them; and it is the more essential that these hours should be adopted in the present inquiry, because the series of observations made at intervals terminated by these hours can the more readily be used in connexion with those made contemporaneously on land, and will also serve to carry on investigations previously instituted, and which have received considerable illustration by means of observations at the regular meteorological hours; we therefore recommend their general adoption in all observations conducted at sea. It is intended in the sequel to call attention to particular parts of the earth's surface where it is desirable that additional observations should be made, in order to furnish data of a more accurate character, and to mark more distinctly barometric changes than the four daily readings are capable of effecting. The best means of accomplishing this for the object in view appears to be the division of the interval of six hours into two equal portions, and to make the necessary observations eight times in the course of twenty-four hours. In the particular localities to which allusion has been made we recommend the following as the hours of observation:-- A.M. 3, 6, 9, noon. P.M. 3, 6, 9, midnight. In other localities besides those hereafter to be mentioned, when opportunities serve, readings at these hours would greatly enhance the value of the four daily readings.