August 2, 1883] 



NA TURE 



333 



velocity. Similarly the bright dry weather of an anticyclone is 

 certainly due to the descending current found round its centre, 

 and so on for every shape of isobars. Any reference to these 

 movements was, however, intentionally omitted by the authors, 

 as these movements are still to a certain extent only partially 

 understood, and it was their desire to rest the explanations which 

 they gave exclusively on observation without reference to any 

 theoretical considerations. 



In a cyclone the broad features of the weather are a patch of 

 rain near the centre, surrounded by a ring of cloud. But if we 

 write down on a diagram, as in Fig. I, the details of weather and 

 kind of cloud in the different portions of the cyclone, we find that 

 many of the best-known prognostics owe their value to the fact 

 that they are characteristic of the front of a cyclone, and that 

 after they have been observed, the rainy portion must pass over 

 the observer before the sky becomes clear again. Sometimes a 

 cyclone, after crossing a [ortion of the British Isles, dies out, 

 and then the prognostics will fail in some districts. 



The prognostics of settled fine weather are shown to be cha- 

 racteristic of anticyclones, which are nearly stationary for several 

 days, and even weeks, together. 



Though the bulk of British weather is made up of cyclones 

 and anticyclones, there are two other distributions of pressure, 

 marked out by wedge-shaped isobars and straight isobars respec- 



100 - BO 



tively, which are associated with many well-known sayings. The 

 chief interest in these prognostics consists in the contrast which 

 they present to cyclone prognostics, as in many cases they aTe 

 associated with fine and dry weather as opposed to the damp of 

 an approaching cyclone. 



In the front of wedge-shaped isobars (which are frequently 

 found between a retreating and advancing cyclone) the weather 

 is beautifully fine, of the sort of which we should say that it was 

 " too fine to last " ; or, if it lasted a whole day, we should call 

 it a *' pet day." 



During the day the sun is hot, at night white frost forms. Great 

 visibility, with a blue sky, and unusual refraction, are often 

 observed. 



On the west side of the wedge-shaped area, as the new cyclone 

 comes on, the blue sky gradually assumes a dirty appearance, 

 accompanied by a halo, and gathers into cloud, and later on rain 

 begins to fall ; while in the southern portion the rain is often 

 preceded by cirrus stripes, either lying with the wind, or some- 

 times at right angles to it. 



" Cirrus at right angles to the wind is a sign of rain." 



These are all shown in the diagram (Fig. 2). 



Some very interesting rain prognostics are also associated with 

 straight isobars. While those in a cyclone are preceded by an 

 almost ominous calm, and a dirty, murky sky, these are associated 



with a hard sky and blustery wind, of which it would be ordi- 

 narily remarked that " the wind keeps down the rain," or that, 

 "when the wind falls, it mil rain." While also the prognostics 

 which precede cyclone rain hold good for the reason that they 

 are seen in front of the rainy portion, those associated with 

 straight isobars hold good because, though there is little rain 

 actually with them, the area which they cover to-day will 

 probably be covered by a cyclone to-morrow — the conditions 

 being favourable for the passage or formation of cyclones. 



Altogether, about 100 prognostics are associated with these 

 four shapes of isobars. 



The use and position of prognostics relative to forecasting 

 from synoptic charts was stated thus : — 



Theoretically, when the isobars are well-defined, we ought to 

 be able to write down the prognostics which might be visible, 

 but practically we cannot do so. Besides, there are sometimes 

 cases of isobars which have no well-defined shape, but with 

 which thunderstorms or heavy showers often occur. These, as 

 is well known, hardly affect the barometer, but are abundantly 

 forewarned by the commonest prognostics, and as the rainfall is 

 usually heavy in them, the failure of the forecast which omits to 

 notice them is very conspicuous. 



The scope of the paper precluded entering into the compli- 



cated question of the non-cyclonic rainfalls in this country. It 

 was only stated that the prognostics which precede them are 

 Bather those associated with broken weather, such as bright 

 sunrise or heavy clouds banking up without the barometer 

 falling, than the muggy, dirty weather of a cyclone front. The 

 warning they give is also much shorter, rarely more than three 

 or four hours, if so long. 



The other paper is an attempt to classify certain types of 

 British weather. 



It is familiar to many observers that the weather in this 

 country frequently occurs in spells of several weeks' duration, 

 during which there is a remarkable persistence of the general 

 type of weather overriding both a considerable fluctuation from 

 day to day, and a considerable local variation from place to 

 place. 



For instance, the wind will often back to some point of 

 south with a high temperature, a dull sky and rain, and then 

 veer to some point of west with a cooler air and brighter sky ; 

 and after a day or so of fine weather it will back again to the 

 south with bad weather, perhaps this time rising to the intensity 

 of a gale, and subsequently veer towards the west with finer 

 weather, and so on for weeks together. 



The changes only vary in intensity and detail, not in general 



