In sketching out a system of observation having especial reference to atmospheric waves and rotatory storms, regard has been had--_first_, to the instruments that should be used, the observations to be made with them, the corrections to be applied to such observations, and the form of registry most suitable for recording the results: _second_, to the times of observation: _third_, to the more important localities that should be submitted to additional observation: _fourth_, to peculiar phaenomena requiring extraordinary observations for their elucidation: and _fifth_, to particular seasons, when the instruments should be watched with more than ordinary care. The more important objects of observation having especial reference to atmospheric waves are those points which have been termed _crests_ and _troughs_. These are simply the _highest_ and _lowest_ readings of the barometer, usually designated _maxima_ and _minima_, and should for the object in view receive particular attention. Whenever there is reason to believe that the barometer is approaching either a _maximum_ or _minimum_, additional observations should be resorted to, so as to secure as nearly as possible _the precise time_ as reckoned at the ship, with her position, of its occurrence, as well as the altitude of the mercurial column at that time and place. By means of such observations as these on board several ships scattered over the surfaces of our great oceans, much valuable information may be accumulated of a character capable of throwing considerable light on the _direction_ in which the lines of barometric maxima and minima stretch, and also a tolerably accurate notion may be formed of their progress, both as regards direction and rate. In immediate connexion with such observations particular attention should be paid to the direction of the wind according to the season. SECTION I.--INSTRUMENTS. _Description and Position of Instruments._--The principal instrument requisite in these observations is the barometer, which should be of the marine construction, and as nearly alike as possible to those furnished to the Antarctic expedition which sailed under the command of Sir James Clark Ross. These instruments were similar to the ordinary portable barometers, and differed from them only in the mode of their suspension and the necessary contraction of the tubes to prevent oscillation from the motion of the ship. The barometer on shipboard should be suspended on a gimbal frame, which ought not to swing too freely, but rather so as to deaden oscillations by some degree of friction. To the upper portion of the tube in this construction of instrument light is alike accessible either in front or behind, and the vernier is furnished with a back and front edge, both being in precisely the same plane, nearly embracing the tube, and sliding up and down it by the motion of rack-work; by the graduation of the scale and vernier the altitude of the mercury can be read off to .002 inch.