siderably displaced. Instead of lying to the west of Scotland, the centre of cyclone activity appeared to lie between England and Norway. This, of course, made England wetter, and the north-west of Scotland drier than usual; but it will take many years before we are justified in saying that this displacement was due to the influence of solar spots.

It is, no doubt, a very tempting ideal to look at the sun as the prime mover of the atmosphere, and to endeavour to follow variations in the heat or energy of his action into their final products as wind or rain. But when we consider what the real nature of weather is, as revealed to us by means of synoptic charts, we see at once that, though undoubtedly an alteration in the sun's power would sooner or later be reflected in his results, any attempt to deduce one from the other directly must lead to disastrous failure.

RELATION TO FORECASTING.

Though opinions will doubtless differ as to whether we are justified in asserting that there is any connection between sun-spots and weather, there is no uncertainty as to what the value of that knowledge would be to a forecaster.

The author believes himself that there are signs of some real relation between the extent of spots on the sun's surface and the rainfall curve at Rothesay, but how should we fare if we tried to forecast the rainfall for any particular year? The most cursory glance at the two curves of sun-spots and rainfall will show that,

if we were to attempt to forecast rainfall on the assumption that the amount would follow the sun-spot curve, we should get just the same unsatisfactory results as if we attempted to forecast the temperature at different hours by reference to the mean diurnal curve of heat. Every meteorological element depends for its value on the balance of several nearly equal forces, so that an attempt to forecast the resulting value by means of the variations of one of these forces can only lead to failure.

So far for the use of the knowledge even of a certain cyclic period in forecasting the character of a year as a whole; and it is still more impossible to use any abstract periodicity in forecasting the weather for any particular day. We shall see in a future chapter that all weather prevision depends on the estimate which an experienced forecaster can make as to the probable path of any cyclone, or as to the formation of a new one. How much would the abstract knowledge that it was a maximum or minimum sun-spot year help him to form such a judgment? Obviously nothing.

On the whole, then, we may say that though there are certainly very strong grounds for the belief that there is some real connection between the state of the sun's surface and terrestrial weather, still, from the nature of atmospheric circulation, we are unable to utilize this fact in forecasting weather, either for any season or for any day.

CHAPTER XIII.

TYPES AND SPELLS OF WEATHER.

INTRODUCTORY.

IN the foregoing chapters we have devoted our attention more to the nature of the causes which produce weather at any moment than to the sequence of weather for several consecutive days. We have, in fact, rather described the nature of the individual disturbances which form, as it were, the units of weather, than the manner in which these components move or follow one another. The word “weather" is used by meteorologists in a twofold sense. When they talk of the weather at a moment, they use the word in a restricted signification, referring to the appearance of the sky, or to the occurrence of rain, snow, etc. When they talk of weather for a longer period, as, for instance, a wet week, or a cold month, they use the word in a more extended sense, and include the sequence of every meteorological element for the time in question.

We have already mentioned that in the temperate zone the units of weather, such as cyclones or anticyclones, are perpetually moving or altering their shape, and thereby producing changes of weather; or to put it

more formally, weather in the temperate zone is the product of the passage of cyclones, anticyclones, or of the minor forms of isobars.

We have also pointed out that all forecasting depends on the limited power which we possess of knowing beforehand what the path of any disturbance is likely to be, or what new changes in the distribution of pressure will probably take place. For instance, if we see a cyclone approaching our own country at eight o'clock in the morning, how can we tell in what direction it will move, or if it is likely to grow more or less intense? If we see an anticyclone, are there any signs by which we can know whether it is going to remain stationary, or to break up and disappear?

When we have examined a very large number of synoptic charts we soon see that, though no two are alike, there is much in common so far as their sequence is concerned. Though a cyclone may move in any direction, and almost with any velocity, nothing is a matter of accident, but certain types of motion are associated with certain types of general pressure distribution.

Our purpose in this chapter is to explain the nature of these changes, by giving in some detail the four great types of weather which occur in Western Europe, with shorter notices of those in the United States and in the tropics. In doing so we will bear in mind the twofold object of all scientific meteorology—the explanation of past weather by reference to the motion of cyclones, etc., and the classification of typical changes with reference to future forecasts.

Long verbal descriptions of complicated weather

maps are not only tedious, but unintelligible to all except those who have made synoptic charts their special study. As our object is to convey an idea of the nature of weather-changes to those who have no previous knowledge of the subject, we shall, therefore, rather trust to copious illustrations of carefully selected specimens, and the reader must look at them and supply his own descriptions. By this means he will learn the character of atmospheric changes and the ways of cyclones by eye, rather than by reference to any written formula. He will see the rapidity with which these changes take place, and acquire that knowledge of the nature of weather which will enable him to form a just conception of the great problems of forecasting.

We shall assume that he has so far mastered the preceding chapters that, when we talk of a cyclone, he knows that it is equivalent to bad weather-warmth in front, cold in rear, wind according to intensity; and that when we say an anticyclone covers any country, that means generally fine weather-always light wind, but blue sky, mist, heat, or cold, according to the circumstances of latitude or season. Also that the direction of wind is given at once by naming an isobaric shape or any portion of it.

Our illustrative charts, mostly on a uniform scale and projection, embrace an area that extends from the Rocky Mountains to Moscow, and from the equator to Greenland. In all, pressures of 29.9 ins. (760 mm.), and all above, are marked by full isobars, while those below are dotted, so that the reader sees at a glance the broad elative distribution of high and low pressure.