CURVE OF OBSERVATIONS, DUBLIN, FROM JANUARY 30 TO FEBRUARY 11, 1861.

30°F.

The accompanying diagram (p. 253) shows all the circumstances of the week preceding the storm. We see that the equatorial wind (SW.) continued from February 2 to the evening of February 7, when it gave way to a W. wind, and finally settled, at 10 P.M. of the 8th, into a NNE. polar current, at which point it held throughout the storm, which reached its maximum twelve hours after the NNE. wind began to blow. On the night of February 9, it blew from the NE., and so continued for forty hours afterwards. The temperature during the prevalence of the SW. wind and falling barometer was mild, and the air damp, producing a feeling of closeness, from the vapour present in the air. For eight days previous to the minimum height of the barometer, the mean temperature was 49°-7, while, during the three days following the minimum of the barometer, the mean temperatures were

This shows a rising barometer, a falling thermometer, reaching a maximum and minimum respectively at the time of the storm. Such a phenomenon cannot by possibility be confounded with a cyclone, which has a minimum barometer before and up to the middle of the storm, and no such relation of the gale to temperature as Dove has pointed out in the class of storms to which that of February 9 unquestionably belongs. The storm of the 9th was also only the first of a series arising from the same cause

viz. the direct and non-cyclonic collision of the equatorial and polar currents of air. A second gale occurred on the night of the 18th, which was felt severely at Drogheda, Dunmore East, and Penzance, and caused the loss of several vessels. At all three places the wind blew steadily from the SE. A third storm has been reported from London, Chichester, Plymouth and other places on the evening of February 21. It was felt in

Dublin from the SSW., but not severely. At 7 P.M., in London, it was felt at its height; and it is said to have reached 36lbs. per foot, and it had sufficient force to blow down the spire of Chichester Cathedral. According to Dove's theory, these two storms are supplements to the storm of the 9th, and not distinct cyclonic movements.

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III. Storms produced by the Mutual Lateral Interference of two Currents flowing in opposite directions.

IF the two currents, on coming in contact with each other, have altered their paths through any angle, so that they flow in opposite directions in parallel channels, the following question arises: -What conditions will cause mutual lateral displacement after such a state of things as that described is once in existence? The most obvious cause is to be found in the fact that the cold air of the polar current exerts a greater lateral pressure than the warm air of the equatorial current, and, therefore, has a tendency to displace it. If the two currents flow in distinct channels close to each other, and if, moreover, the retardations produced by their contact have ceased, the mean velocity of both will increase. The velocity of the equatorial current will increase more rapidly than that of the polar, inasmuch as the former flows in a channel which is constantly contracting, the latter in one which is constantly expanding. Owing to the fact that the equatorial current continues for a shorter time in contact with the surface of the earth, it will be retarded by friction to a less extent than the polar current will be accelerated by the same cause; or, in other words, the equatorial current will be more deflected towards the W., than the polar towards the E. If, e.g., the bed of the former lies in Europe and of the latter in America, the former will have a tendency to move away from the line of contact, and

thereby will induce the polar current to diverge, as a NW. wind, from its own bed in order to fill the vacuum. If the conditions be reversed, the equatorial current will have a tendency to force its way into the bed of the polar current in a more westerly direction than that of its own proper course. This interference will take place at first in the upper strata of the atmosphere, in consequence of the greater density of the polar current. If the resistance offered by the polar current be so great that the equatorial current cannot force an entry, a cyclone in the direction S., E., N., W., will be generated in the latter. In the case of a regular mutual displacement of the currents, the vane will shift in the direction S., W., N., E., а gyration which is entirely distinct from that produced by a cyclone.

If we take an example, and suppose that in Europe the polar current gives way in high latitudes to the equatorial current, which is nearly due W., the former will veer gradually round to E., and we shall have in the north of Europe very mild weather, with westerly winds; while in the south it will be very cold, with easterly winds. If the E. wind which is thus produced, be checked in its passage towards the W. by the equatorial current, which is still SW. in the Atlantic ocean, we shall have a barometrical maximum over the whole district where the cold E. wind is felt; until at last it forces its way through the SW. wind over the Atlantic ocean, and the barometer falls. Subsequently the southern current, checked in its turn, forces its way back again through the northern current, at first in the upper, afterwards in the lower strata of the atmosphere.

Under the conditions here described, the first cold will come from the NW. after a period of very mild weather, subsequently it will come from the N., and NE. This

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