334 



NATURE 



[August 2, 18S3 



character, while the feel of the weather and the look of the sky 

 remain through all of them what are customarily associated with 

 westerly winds. 



Similarly the wind will often blow persistently from some 

 point of east, fluctuating between south-east for fouler weather 

 and north-east for finer weather, and back again with many 

 variations for several weeks, during which the predominant 

 features of the weather are always characteristic of east winds. 

 The frequent recurrence of particular types of weather at par- 

 ticular seasons of the year is also a matter of common obser- 

 vation ; the north-east winds of March, the cold north winds of 

 the middle of June, and the wet west winds of September are 

 well-known instances. 



If we examine a large number of synoptic charts we find that 

 relatively to Europe the general position of the great areas of 

 high pressure frequently remained constant for a lengthened 

 period. Further examination shows that the constancy of these 

 positions coincides with persistent types of weather similar 

 to those above mentioned, the fluctuation of type being due to 

 the passage of cyclones, while the local variation depends on the 

 position of the cyclone centres and on the innumerable local 

 conditions which modify any general type. 



Over the North Atlantic and Europe the distribution of atmo- 

 spheric pressure presents certain constant features, namely — 



1. An equatorial belt of nearly uniform low pressure. 



2. A tropical belt of high pressure rising at intervals into 

 great irregular elevations or anticyclones. 



3. A temperate and Arctic region of generally low pressure, 

 but in which occasionally areas of high pressure appear for a 

 considerable period. 



The equatorial belt constantly covers the Sahara and the 

 Amazon valley, and always narrows over the Atlantic at about 

 30 west longitude, where it often does not reach higher than 10° 

 north latitude. The shape and depth of this area are tolerably 

 constant. 



The tropical belt comprises a region of high pressure rising 

 at variable intervals into great anticyclones. Their position is 

 generally variable, with the exception of one, which is always 

 found over the central Atlantic. This anticyclone forms a very 

 important factor of the weather of western Europe, and will be 

 constantly referred to as "the Atlantic anticyclone." Its ex 

 tension south and west is tolerably constant, while towards 

 north and east it is variable, sometimes rising as far as 60° north 

 and stretching over Great Britain and continental Europe. 



The temperate and Arctic region extends from the tropical 

 high pressure belt to the pole. The pressure, though ordinarily 

 low, is perpetually fluctuating by reason of the incessant passage 

 of cyclones ; yet occasionally persistent areas of high pressure 

 appear in certain portions of it. 



With reference to western Europe there are at least four per- 

 sistent types of weather — 



1. The southerly, in which an anticyclone lies to the east or 

 south-east of Great Britain, while cyclones coming in from the 

 Atlantic either beat up against it or pa^s towards north-east. 



2. The westerly, in which a tropical belt of anticyclones is 

 found to the south of Great Britain, and the cyclones which are 

 formed in the central Atlantic pass towards east or north-east. 



3. The northerly, in which the Atlantic anticyclone stretches 

 far to the west and north-west of Great Britain, roughly cover- 

 ing the ocean. In this case cyclones spring up on the north or 

 east side, and either work round the anticyclone to the south- 

 east, or leave it and travel rapidly towards the east. 



4. The easterly, in which an apparently non-tropical anti- 

 cyclone (or one disconnected with the tropical high-pressure belt) 

 appears in the north-east of Europe, rarely extending beyond the 

 coast-line, while the Atlantic anticyclone is occasionally totally 

 absent from the Bay of Biscay. The cyclones, then, either come 

 in from the Atlantic and pass south-east between the two anti- 

 cyclones, or else, their progress being impeded, they are arrested 

 or deflected by the north-east anticyclone. Sometimes they are 

 formed to the south of the north-east anticyclone, and advance 

 slowly towards the east, or in very rare instances towards the west. 



The details of the southerly and westerly types are given in 

 the paper. Here we can only reproduce the three diagrams of 

 the westerly type, Figs. 3, 4, and 5, in which the general charac- 

 teristics of the type, just mentioned, are readily seen. 



The value of the recognition of type groups is shown in the 

 following ways : — 



1. They explain many phenomena of weather, and many 

 popular prognostics. 



For instance, besides showing *h» nature of spells of good, 



bad, dry weather, &c, they explain by reason of their per.-istence 

 such prognostics as why " grouse coming down into farmyards are 

 a sign of snow." Also why the prognostics, " When a river 

 like the Tweed rises without any rain having fallen," or "Irre- 

 gular tides are ^gns of rain," have a significance for the future ; 

 for though bith are caused by past bad weather at a distance, 

 yet the persistent type will almost certainly sooner or later bring 

 more bad weather over the place of observation. 



Then the recurrence of hot and cold periods, many of them 

 well known, are shown to be due to the recurrence of a similar 

 type of pressure distribution about the same season of the year. 

 Particulars of seventeen such are given, and the manner in which 

 the knowledge of them can be utilised in forecasting is stated 

 thus: that though the forecaster is not justified in stating that 

 any period will occur absolutely, still when about the time of its 

 usual recurrence the synoptic charts show signs of the expected 

 type, then the forecasts for a few days ahead can be issued 

 with greater confidence. For instance, suppose that about 

 November 6 — a cold period — the charts begin to show traces of 

 the northerly type, then, but not before, there would be good 

 grounds for saying that a period of cold weather, which usually 

 occurs at this season, has already set in, and may be expected to 

 last for five or six days, the forecaster being thus enabled to issue 

 a much longer forecast than can as a rule be safely attempted. 



2. Type groups are of the utmost value in forecasting, for 

 when the existence of the type is fairly recognised then the 

 general features of the weather are at once given, as well as 

 the probable motion of the cyclones which are formed during 

 the continuance of the type. Unfortunately in many cases no 

 certain indications can be given of an approaching change of type. 



3. Statistical results can be corrected by their means, for they 

 give a true test of identity of recurrent weather, which no single 

 item, such as heat, cold, rain, &c, can do. 



4. They enable geological questions to be treated, such as the 

 influence of changing distribution of land and sea on climate, 

 in a mire satisfactory manner th-n any other method. 



The general principles of prognostics and types hold all over 

 the world, but the details in these papers apply to Great Britain 

 only. Ralph Abercromby 



OUR ASTRONOMICAL COLUMN 

 The Great Comet of 1SS2.— It appears quite possible that 

 as the moon draws away from the morning sky towards the end 

 of the present month, this comet may be again observed with 

 our larger instruments. Its distance from the earth has been 

 increasing from soon after perihelion passage in September last, 

 and a maximum takes place at the beginning of September next, 

 when the distance is 5'9SS ; the earth then for a time overtakes 

 the comet, and the distance diminishes to 5709 on December I. 

 The intensity of light, however, is greatest at the end of August, 

 and the comet then rises at a sufficient interval before the sun to 

 render observation feasible. It will at least be of much interest 

 to ascertain if the comet can be reached with our most powerful 

 telescopes. The only comet which has been hitherto observed 

 under similar conditions is the celebrated one of 181 1, which, it 

 may be remembered, was observed by Wisniewsky at Neu- 

 Tscherkask, in August 18 1 2. 



The following places are deduced from the elliptical elements 

 calculated by \V. Fabritius of Kiev {Astron. Nac/i., No. 2514), 

 from a wider arc of observation than any other orbit yet 

 published : — 



At Greenwich Midnight 

 R.A. N.P.D. Log. distance from 



h. m. s. „ , Earth. Sun. 



Aug. 28 ... 72558 ... 9832-0 ... 07773 ■•- 07306 



30 ... 7 26 44 ... 98 41*6 

 Sept. 1 ... 7 27 28 ... 98 5i - 4 ••• 07773 •■• o - 7339 

 3 ... 7 28 10 ... 99 i'4 



5 ... 7 28 49 ... 99 »'5 ••• 07771 ••• 07372 

 7 ... 7 29 26 ... 99 217 

 9 ... 7 30 o ... 99 32-1 ... 0776S ... 07405 



Dr. Julius Schmidt last saw the comet at Athens on April 28 ; 

 in a letter addressed to Nature, Mr. A. S. Atkinson of Nelson, 

 N.Z., states that with a 4-inch refractor he saw it with certainty 

 on May 6. Assuming the theoretical intensity of light on the 

 latter date to be unity, the intensity on August 28 is 0-35. 



The Astronomische Gesellschaft.— The next meeting 

 of this society will be held at Vienna, in the apartments of the 

 Academy of Sciences, from September 14-17, under the presi- 



