August, 1903. 



KNOWLEDGE, 



173 



be doubted whether any of the enterprises to which it may 

 be harnessed, as it were, will prove so interesting as wlien 

 it comes to be employed in the business of forecasting the 

 weather. At present the weather prophets are doing the 

 best they can with the ordinary method of sending tele- 

 graphic messages, and considering the many obstacles in 

 the way, it must be conceded l)y any unbiased critic that 

 they do very well indeed. The mere fact, however, that 

 there are so many miles of wire, and so many post offices, 

 between the officials at the central office, where the fore- 

 casts are prepared, and their observers who send them the 

 daily reports of the weather, is a serious hindrance to 

 progress, and it will Ije a happy day for the weather 

 prophets when these intermediaries are abolished. 



The general methods by whicli a modern forecast of the 

 weather is produced have, to many people, an air of 

 mystery, and to the uninitiated few things seem so mys- 

 terious and complicated as a weather chart. Most 

 countries nowadays have established offices whei'e such 

 charts are daily compiled, and in all of them the method 

 of procedure is the same. The object aimed at is to 

 ol)tain a general notion of the state of the weather at a 

 given hour over a large tract of country. To this end a 

 large number of oliservatories or stations are established 

 in many different localities, it being the duty of the 

 observers to make reports of the weather two or three 

 times a day. The information specially asked for refers 

 more especially to the height of the barometer, to the 

 direction and force of the wind, the state of the sky as 

 regards cloudiness, the temperature of the air, and the 

 amount of rainfall. During a great number of years 

 these observations have been taken in the British Isles 

 three times a day — at 8 a.m., 2 p.m., and 6 p.m. 



Now, in order that this information may l)e of the greatest 

 amount of service, it is important that it should arrive 

 at the head office promptly. The messages accordingly 

 are forwarded by telegrajjli, so that at the earliest oppor- 

 tunity they may be plotted on to a chart or map. With 

 this weather chart in front of him the official weather 

 forecaster is accordingly informed as to the places where 

 the barometer is rising and where it is falling. On this 

 information he bases his forecasts, and issues, if need be, 

 his warnings as to approaching storms and gales. The 

 reports, moreover, that are tel('graj)hed at other times 

 during the day greatly help as regards giving information 

 concerning the dii-ection in which any storm may be 

 travelling. For instance, the chart may show that a storm 

 lias arrived on the west coast of Ireland, and the important 

 thing to know is whether it seems more likely to move 

 north-eastwards across Scotland or south-eastwards across 

 England. It is indeed at such a time as this that the 

 most difficult problems arise, and the mistakes made by 

 the weather prophets are generally due to the fact that the 

 storms suddenly move off in an unexpected direction. 

 Speedy and prompt infonnation from the observing 

 stations is therefore of the highest importance. 



Something of the difficulties of the case are understood 

 when the mechanism, so to speak, of one of these revolving 

 storms, cyclones, or depressions, as they are variously 

 called, is examined. Such aerial eddies may be likened 

 to the dimples seen in every running stream of wattn-, 

 for not only have they a rotatory movement, but, 

 lik(^ the dimples, they also travel onwards. Cyclones, it 

 should be remarked, vary v(Ty greatly in size, and 

 their diameter may be anything from a few yards up 

 to a thousand miles. The smallest of them may be 

 seen at any street corner on a windy day, -and, indeed, a 

 little time spent in watching these miniature whirlwinds 

 will give a very fair idea of tlie (uvuses which produce the 

 larger atmospheric cyclones. Intermediate between tlie 



small eddies and the full-grown storms are the whirlwinds 

 and dust storms which career across many of the deserts 

 and arid plains ; while in this same category are also to te 

 included the waterspouts that spring up over the sea and 

 some of the larger lakes. All these phenomena are nearly 

 related, and in each there is a rotatory as well as an 

 onward movement. A very fair representation of a 

 revolving cyclone may be drained by turning a stick 

 very quickly in water, and it will !« noticed that the 

 faster the water is made to revolve the deeper does the 

 dent or hollow in the wat«r become. There is a similar 

 relationship between the depth of a cyclone and tlie 

 velocity of the winds blowing around it. At the centre of 

 every storm the atmospheric pressure is greatly deficient, 

 and' the barometer falls to a low level. This pressure 

 increases outwards from the centre of the system, the 

 barometer rising higher and higher towards the outer edge 

 of the storm. Now, when the slope from the outside edge 

 to the centre is very abrupt, like the descent to certain 

 valleys, the barometric gradients are said to lie very steep, 

 and it is at such times as these that the wind attains its 

 greatest force. All these, then, are matters that are 

 clearly set forth on a weather chart, and with this 

 information before him the weather forecaster can readily 

 see whether the storm is a severe one, or, in other words, 

 he is able to see whether the atmospheric vortex is very 

 deep. 



It is, however, when the attempt is made to forecast the 

 future movements that the difficulties begin, and it is at 

 this point that wireless telegraphy woidd prove of the 

 greatest assistance to the hapless weather prophets. A 

 few years ago many of the newspapers published stomi 

 warnings sent from America, the idea being that storms 

 observed to be setting forth from the American shores 

 would eventually reach the British Isles or some other 

 part of Western" Europe. Commonly, the warnings stated 

 that between such and sucTi dates a storm might be 

 expected to show itself on the French, British, or Nor- 

 wegian coasts, the margin both as regards time and 

 place being large. But many of the storms never arrived, 

 having possibly blown themselves out during their journey 

 across the Atlantic, while others, instead of taking a day 

 or so over the voyage across, would loiter aboiit for days 

 so that the storms failed to put in an appearance or 

 arrived in unexpected ))laces at unex])ected tunes. The 

 experiment of sending the storm -warnings was, however, 

 an interesting one, for it recognised the fact that these 

 cyclones make long journeys without losing their identity, 

 and from this point of view these warnings therefore had 

 their uses. 



Contrasted with the weather forecasters in America, the 

 British officials are placed at a great disadvantage, for 

 instead of having a wide continental area to the westward 

 of them, they are ln)unded by the Atlantic Ocean. All 

 storms, owing to the deflecting movements of the earth as 

 it rotates on its axis, travel from west to east, so that it is 

 the desire of all weather forecastei-s to obtain early and 

 prompt information from as many places to the westward 

 of them as possibh-. In this rcsfK^ct it will l>e seen that a 

 forecaster, say at \Vashingti)n, is well situated, for to the 

 westward of him he has many observers who send him all 

 the latest information, so that it is much easier to trace the 

 daily progress of a storm as it blusters across the country. 

 But the British forecasters are in much worse case, for 

 they often do not know of the existence of an on-coming 

 storm until it has actuallv appeaivd on the west coast of 

 Ireland. The problem, therefore, that has always pre- 

 sented itself has been as to the best means to be adopted 

 for finding out what was happening away out iu the 

 Atlantic. 



