The Hurricane Guide | Page 4

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 a?rial 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 ph?nomena 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 ph?nomena 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 ph?nomena of storms and waves. It is also very desirable that our knowledge of these ph?nomena 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 ph?nomena 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