268 



DISCOVERY 



more fanatical Arabs destroyed in time the tolerant 

 character of the early Osmanli government, but Dr. 

 Gibbons' book is a curious commentary on a manifesto 

 issued some months ago by a number of his most dis- 

 tinguished compatriots in America, in which it was said 

 that " five hundred years ago the Turk entered Europe 

 with a sword, with massacre, with outrage, with pitiless 

 persecution." Our policy towards the Turks should 

 be based on principle and not upon history, but if his- 

 torical arguments are introduced, they should be real 

 history. 



Modern Methods 

 of Weather Forecasting 



By Donald W. Horner, F.R.A.S., 

 F.R.Met.Soc. 



The empirical methods that were good enough for our 

 forefathers have, during the past half-century, given 

 place to a scientific system of weather forecasting, 

 based upon synoptic weather charts constructed 

 from information received by telegraph from various 

 stations situated throughout Western Europe, and also 

 from w^ircless messages from ships in the Atlantic Ocean. 



It must be admitted that, notwithstanding all this 

 mass of information and every precaution that may be 

 taken to ensure the correctness of forecasts, there are 

 times when the forecast fails altogether, or arrives too 

 late (in the case of storm warnings) to be of use. Cases 

 of this sort, however, become more rare year by year, 

 ninety-five per cent, of the forecasts now made by the 

 British Meteorological Office being correct in most 

 details, the remaining five per cent, only being com- 

 plete failures. This work, undertaken on a sea-girt 

 island like ours, with only wireless information from 

 moving ships upon which to depend towards the west- 

 ward, the direction from which most storm-bearing 

 depressions come, compares very favourably with that 

 of the United States Weather Bureau, whose percentage 

 of successful forecasts, with a vast continent covered by 

 a network of local forecast officials, amounts to ninety. 



That these few failures may in due time be eliminated 

 is shown by the continuous advances made in recent 

 years. 



The Forecast Division of the British Meteorological 

 Office now has its headquarters quite separately at 

 Kingsway, London, W.C.2, the original buildings at 

 South Kensington being used only for climatological 

 purposes. A third branch of the Meteorological Office 

 is the recently-taken-over offices of the British Rainfall 

 Organisation at 62 Camden Square, London, N.W.i, 

 under the able superintendentship of Mr. Carle Salter, 



F.R.Met.Soc' This is what may be termed a branch 

 of the Climatological Section, as the observations o! 

 rainfall, gathered together annually by over 5,000 

 voluntary observers, are very valuable, and are pub- 

 hshcd annually in volume form in British Rainfall. 



But in following chmatology, we have left our original 

 subject of forecasting. 



The name forecast was invented by Admiral Fitzroy 

 more than sixty years ago, and it is to the original idea 

 propounded by him at that time that we owe the 

 elaborate system of forecasting by means of synoptic 

 weather charts practised in the present day. 



The first forecasts were issued in 1861, and at an 

 even earlier date storm warnings to sailors and fisher- 

 men were exhibited on our coasts. 



At first these took the form of drums, but these have 

 been superseded by cones : the south cone, having its 

 point downwards, being hoisted on the harbour flag- 

 staff when gales are expected from the south-east, 

 south, south-west, or west, veering north-west ; and 

 the north cone when the storm is anticipated from the 

 north, north-east, east, or north-west, veering to the 

 northward, but not when backing westward. 



The weather maps published daily in certain news- 

 papers are thus prepared : 



The state of the weather, sky, and direction of the 

 wind are taken at a large number of stations in the 

 British Isles, the continent of Western Europe, and 

 at the Azores, at 7 a.m. G.M.T. These observations, 

 together w-ith readings of the mercurial barometer in 

 millibars and of the thermometer in degrees absolute, 

 on being received at the Central Office of the Forecast 

 Division, are plotted by skilled cartographers on charts, 

 forming what is known as a sjmoptic chart, a term 

 which will be explained later. 



These charts are lithographed for the Daily \\'eather 

 Report, which is sent out to subscribers by post, and 

 at 6 p.m. electros of similar charts are supphed to 

 newspapers wiUing to give sufficient space to the sub- 

 ject. The papers at present reproducing them are The 

 Times, Daily Telegraph, and Morning Post. 



These maps consist of the contour lines of North- 

 western Europe, having the lines of equal barometric 

 pressure (isobars) drawn thereon. These isobaric 

 lines are drawn through all places having an equal 

 pressure at the same instant of time ; e.g. on June 17, 

 1919, the evening weather map showed that the baro- 

 metric reading of 1020 mb. (30.12 in.) started from the 

 coast of France, passed over the Essex side of the 

 Thames estuary, and across London to the Irish 

 Channel, and over to the West of Ireland. The next 

 isobar (1018 mb.) ran across the centre of England and 



Voluntary observers are always welcomed for this section, 

 and a post-card to the Superintendent will bring a reply as to 

 where fresh rainfall records are most required. — D. \V. H. 



