STEREOSCOPIC MAP OF THE “WINDS ALOFT”
[(Larger)]

There are a few conspicuous points of difference between the weather maps issued in foreign countries and those issued in this country. Thus a majority of the foreign weather services publish two or more charts on the same sheet; either for the sake of showing different meteorological elements separately or, in most cases, to represent the conditions prevailing not only at the hour of the current morning observation, but also at certain hours of the previous day. One of the three editions of the British map includes four charts, corresponding to observations at four different hours. By means of such series of charts one can observe the recent changes of weather as well as the current conditions. Weather maps published in the United States show primarily the conditions at 8 a. m., Eastern Standard Time, of the morning of issue; though certain features of past weather are also indicated, including changes of temperatures, movements of storm centers, etc. Evening maps are drawn at Washington and at many other places, but are not published.

In this country the publication of weather maps has been carried out on a much more liberal scale than elsewhere. Instead of issuing maps at only one or a few places, as is the custom in other parts of the world, it has been the policy of the American service to publish them at populous centers all over the country. In some cases they are printed or manifolded at the local Weather Bureau station, and distributed by mail and messenger; in other cases they are published in the newspapers. The daily circulation of the maps has thus, at times, run up into the millions. This comprehensive duplication of the chart is made possible by special arrangements with the telegraph companies. The reports of observations are, to a large extent, sent over circuits, along which the telegraph offices, besides forwarding the local report, copy the reports from other stations as they pass over the wires. Certain stations, forming connecting links between the circuits, effect the transfer of collected reports from one circuit to another; so that, in a very short time, upward of 150 stations receive the reports from a large number of other stations. The maps issued at stations or published in newspapers are generally rather crude, though they answer their purpose; but the large lithographed map issued every day at the Central Office, in Washington, is much the most artistic production of its kind published anywhere in the world.

ENLARGED SECTION OF THE STEREOSCOPIC WIND MAP

Large weather maps, drawn with colored chalk on a ground-glass base, may be seen at certain produce exchanges and railway stations, on the “boardwalk” at Atlantic City, and in the Capitol at Washington. Motion-picture weather maps, made from series of maps showing conditions at successive intervals of time, have been prepared experimentally in this country and abroad.

The reports used in the construction of weather maps are telegraphed from the stations in cipher, in order to save expense. In Europe groups of figures are used for this purpose, but the United States Weather Bureau makes use of a word code, which offers the advantage over a figure code that, as a rule, mistakes in the telegrams can easily be detected by anybody familiar with the code. The American weather code is something of a literary curiosity. In each of the many thousand words it contains there are certain significant letters, and these must fall in certain sequences in order to convey the information required. The English language has been ransacked—and somewhat stretched—to secure the necessary words. Observers consult the code book in enciphering their reports, but translating is easily done without the book by those who have mastered the relatively simple principles on which the code is constructed.

SIMPLIFIED WEATHER MAP FOR JAN. 25, 1905, 8 A. M., EASTERN STANDARD TIME

The language of lines, shadings and symbols used in weather maps can be learned in a few minutes, and it is, as a rule, fully explained on the face of the map. This is true of foreign maps as well as American. A full-fledged weather map is hardly susceptible of reproduction in a book of ordinary dimensions. The simplified map that we show here, taken from a Weather Bureau bulletin, will, however, serve to illustrate some of the features of such publications. The reader should first fix in his mind the explanations printed at the lower left-hand corner of the map and then study the map in the light of what has been said in Chapter VIII about the circulation and movements of highs and lows. On this map we have an exceptionally well-developed high over the middle of the country and a pronounced low on the Atlantic coast. The former, with clear skies and very cold weather, constitutes a cold wave. The latter is attended by a widespread snow storm and, as may be inferred from the crowded isobars, by stormy winds.