at right angles to those supposed to exist by the Professor. These currents were N.W. and S.E. with a lateral motion towards the N.E. He also carefully discussed the barometric phænomena with relation to both these sets of currents, and arrived at the following conclusions. The details will be found in the author's third report, presented to the British Association for the Advancement of Science (Reports, 1846, pp. 132 to 162). During the period under examination the author found the barometer generally to rise with N.E. and N.W. winds, and fall with S.W. and S.E. winds, and that the phænomena might be thus illustrated:—Let the strata a a a' a', b' b' b b, fig. 3, represent two parallel aërial currents or winds, a a a' a' from S.W. or S.E., and b' b' b b from N.E. or N.W. and conceive them both to advance from the N.W. in the first instance and from the S.W. in the second, in the direction of the large arrow. Now conceive the barometer to commence rising just as the edge b b passes any line of country, and to continue rising until the edge b' b' arrives at that line, when the maximum is attained. It will be remarked that this rise is coincident with a N.E. or N.W. wind. The wind now changes and the barometer begins to fall, and continues falling until the edge a a coincides with the line of country on which b b first impinged. During this process we have all the phænomena exhibited by an atmospheric wave: when the edge b b passes a line of country the barometer is at a minimum, and this minimum has been termed the anterior trough. During the period the stratum b' b' b b transits, the barometer rises, and this rise has been called the anterior slope. When the conterminous edges of the strata a' a' b' b' pass, a barometric maximum extends along the line of country formerly occupied by the anterior trough, and this maximum has been designated the crest. During the transit of the stratum a' a' a a the barometer falls, and this fall has been characterised as the posterior slope; and when the edge a a occupies the place of b b, the descent of the mercurial column is completed, another minimum extends in the direction of the former, and this minimum has been termed the posterior trough.

It will be readily seen that the lateral passage of the N.W. and S.E. currents towards the N.E. presents precisely the same barometric and anemonal phænomena as the rotatory storms when moving in the same direction. If the observer, when the barometer is at a maximum with a N.W. wind, place himself in the same position with regard to the laterally advancing current as he did with regard to the advancing storm, i. e. with his face towards the quarter from which it is advancing—S.W., he will find that with a falling barometer and S.E. wind the current passes him from the left to the right hand; but if at a barometric minimum he place himself in the same position with his face directed to the quarter from which the N.W. current is advancing laterally, also S.W., he will find that with a rising barometer and N.W. wind the current passes him from right to left. Now the two classes of phænomena are identical, and it would not be difficult to show that, had we an instance of a rotatory storm in the northern hemisphere moving from N.W. to S.E., it would present precisely the same phænomena as to the direction of currents passing from left to right and from right to left with falling and rising barometers, increase and decrease in the force of the wind, &c., as the oppositely directed aërial currents do which pass over western central Europe.

In the absence of direct evidence of the production of a revolving storm from the crossing of two large waves, as suggested by Sir John Herschel, although it is not difficult to obtain such evidence, especially from the surface of the ocean, the identity of the two classes of phænomena exhibited by the storms and waves as above explained amounts to a strong presumption that there is a close connexion between them, and that a more minute investigation of the phænomena of atmospheric waves is greatly calculated to throw considerable light on the laws that govern the storm paths in both hemispheres. The localities in which these atmospheric movements, the waves, have been hitherto studied, have been confined to the northern and central parts of Europe—the west of Ireland, Alten in the north of Europe, Lougan near the Sea of Azov, and Geneva, being the angular points of the included area. It will be remarked that the greatest portion of this area is inland, but there is one important feature which the study of the barometer has brought to light, and which is by no means devoid of significance, viz. that the oscillations are much greater in the neighbourhood of water, and this appears to indicate that the junction lines of land and water form by far the most important portions of the globe in which to study both the phænomena of storms and waves. It is also very desirable that our knowledge of these phænomena should, with immediate reference to the surface of the ocean, be increased, and in this respect captains and masters of vessels may render essential service by observing and recording the state of the barometer, and direction and force of the wind, several times in the course of the day and night;[3] and when it is considered that the immediate object in view is one in which the mariner is personally interested, and one in which, it may be, his own safety is concerned, it is hoped that the keeping of a meteorological register having especial reference to the indications of the barometer, and force and direction of the wind, will not be felt as irksome, but rather will be found an interesting occupation, the instruments standing in the place of faithful monitors, directing when and where to avoid danger, and the record furnishing important data whereby the knowledge of general laws may be arrived at, having an essential bearing on the interests of the service at large.

CHAPTER III.

OBSERVATIONS.

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 phænomena 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