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intensity of this Some days the

not necessarily storms. The size and cyclone varied every day of its life. intensity was so great that the wind rose to the force of a gale in places; other days the gradients were never developed of sufficient steepness to give rise to more than a breeze. No general rule can be laid down that will apply to the life-history of a cyclone; we must watch from day to day for symptoms of increasing or decreasing intensity.

From all this we can also estimate the value of the idea that a swift Atlantic mail-steamer could arrive before a storm, and so give notice of approaching danger.

The cyclone which we have just traced travelled rather slower than usual; we often find depressions cross the Atlantic in four days. However, in this case, the cyclone came across at just about the speed of the fastest steamers. The first two days the cyclone would have been passing the vessel; on all the other six days, the steamer would have been catching up the cyclone. The ocean route from the mouth of the St. Lawrence to Cork is almost exactly along the track of this cyclone. A steamer would, therefore, have experienced little wind, but a uniformly low barometer during her voyage. Any report which she alone could give would be useless to a forecaster in London or Paris; but if several boats were arriving, and they all telegraphed up their observations at 8 a.m. on the three or four preceding days, then the combination of their results would certainly enable the forecaster to deduce some useful indications.

In all British forecasting a certain amount of uncertainty must always remain as to the future path of a

cyclone, even when we see a well-defined depression lying off the coasts of Ireland; how much greater must the uncertainty be when we attempt to forecast the path of a cyclone four days ahead, and from a distance of three thousand miles? If the forecaster cannot hit England straight when he aims from Ireland, will he be likely to hit her at all if he shoots from New York? The number of cyclones which actually cross the Atlantic from shore to shore appears to vary from about eight to twenty in any year. In many cases it is difficult to say whether it is the same cyclone which we trace, from the peculiar manner in which two depressions may fuse into a single new one. On the whole, then, we see that the crude notion of forecasting European storms from the United States contains some elements of truth, but that still, from the nature of cyclone-motion, the idea can never be used in practical forecasting.

PATH AS INDICATED BY THE STRONGEST WIND AND HIGHEST ADJACENT PRESSURE.

A good deal of work has been done, both in England and Germany, on the question of how far the path of a cyclone can be determined by the general direction or force of the surrounding wind, and the investigators have found that generally the propagation of the cyclone is in the same direction as the strongest surface-wind in the neighbourhood. There are, of course, a good many exceptions; and it is impossible in our present state of knowledge to say whether the strongest wind indicates the general direction of the generating current in which

the cyclone is only an eddy, or whether the strongest wind is the product of the combination of surface rotation and propagation, being nearly in the same direction at one particular point.

All our charts have shown that a cyclone usually tries to keep an area of high pressure on its right-hand side; and this, too, has a good deal to do with the strongest wind being found at right angles to the centre, and therefore nearly in the same direction as the motion of the whole depression.

INFLUENCE OF SURROUNDING TEMPERATURE.

We now come to the far more difficult but important question as to the influence of surrounding temperature on the propagation of cyclones, and as to whether the development of heat on the right-hand side of a cyclone is the cause or product of cyclone-motion.

Putting all theoretical considerations aside, the facts of the case, as far as Europe is concerned, are as follows:-A cyclone nearly always has the highest temperature on the right-hand side of the path; and for the same distribution of pressure, there is a considerable difference in the path of depressions at different seasons of the year, when the general slope of heat from the equator to the pole is not the same.

Dr. J. V. Bebber has discovered the following relations special for Germany and Central Europe:-"If the distribution of air-pressure and temperature in the neighbourhood of a depression are directed to the same sense, then the propagation of the depression is nearly perpendicular

to the pressure and temperature-gradient. If the airpressure and temperature in the neighbourhood of a depression are distributed in an opposite sense, and if the differences are nearly equal, so is the motion of the depression checked, or even arrested (stationary depression), whereby the depression takes a long, more or less distorted form, of which the longer axis lies perpendicular to both the air-pressure and temperature-gradient. If, with the same distribution as before, either the airpressure or temperature-gradient overweighs on one side of the depression, so will the direction of the path be determined by the predominating element. If air-pressure and temperature are not, indeed, opposite, but also not distributed in the same sense round the depression, so will the depression strike out a resultant direction." He also thinks that pressure is the more important determination of cyclone-motion in winter, and temperature the predominant influence in summer.

The conception of temperature and pressure gradients being distributed in the same or opposite senses, appears to be as follows:-If the highest pressure and highest temperature are either both to the north, or both to the south of a cyclone, they are said to be in the same sense, and the depression will move at right angles to both. But suppose pressure was highest to north, and temperature to south; then these two elements would be distributed in the opposite sense, and the cyclone would probably be arrested in its usual eastward course.

These observations are more suitable to Germany than to Great Britain, as some of the expressions are hardly applicable in the latter country, and in England

local variation is so great, and the area of observation so small, that the distribution of surrounding temperature can scarcely be used in practical forecasting. But in all continental Europe we have one practical rule—that if pressure is high to the north or north-north-east of a cyclone, and temperature also higher on that side than to the south, then the propagation of the depression will probably be towards some point of west, instead of towards the east as usual. For instance, suppose we found some morning a cyclone over Central Europe, with an anticyclone over the North Sea, the natural presumption would be that the depression would move-always very slowly in this type-towards Russia; but if, as in Figs. 95 and 96, we found the highest temperatures in the Baltic, and not in Austria, and especially if the temperature seems to rise to the north or north-west of the centre, then we might forecast that the depression would move, as in this instance, westwards towards Great Britain.

The question how far the cyclone affects temperature, and how far the latter directs the former, will be best explained as follows:-Let us call the general slope of temperature from land to sea, which varies according to the time of year, the "seasonal gradient of heat," and the patch of heat on the right of a cyclone "cyclone heat;" then we may say that, while the seasonal gradient has a directive influence on the path of the depression, the cyclone heat is the product of the moving whirl itself. The conclusive proof that the heat-patch on the right front of a depression belongs to the cyclone directly, and not indirectly, through the disturbance of radiation,

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