68 STORMS AND WEATHER FORECASTS 



over all lines, are speeding to their destinations, each station 

 contributing its own observations and receiving in return, 1)}' an 

 ingenious system of telegraph circuits, such observations from 

 other stations as it ma}^ require. Tlie observations from all 

 stations are received at such centers as Washington, Chicago^ 

 New York, and other large cities, and nearly all cities having a 

 Weather Bureau station receive a sufficient number of reports 

 from other cities to justify the issuing of a daily weather map- 

 Before examining the accompanying ciiarts, it may be well to 

 glance at the Central Office in Washington, while the observa- 

 tions are coming in, so as to get an idea of how the charts are 

 made for the study of the forecast official. From these he gets 

 a panoramic view, not only of the exact conditions of the air 

 over the whole country at the moment of taking the observa- 

 tions one hour before, but of the changes which have occurred 

 in those conditions during the preceding 24 hours. As fast as 

 the reports come from the wires they are passed to the Forecast 

 Division, where a reader stands in the middle of the room and 

 translates the cipher into figures and words of intelligible 

 sequence. A force of clerks is engaged in making graphic rep- 

 resentations of the geographical distribution of the different 

 meteorological elements. On blank charts of the United States 

 each clei'k copies from the translator that part of each station's 

 report needed in the construction of his particular chart. One 

 clerk constructs a chart showing the change in temperature 

 during the preceding 24 hours. Broad, red lines separate the 

 colder from the warmer regions, and narrow red lines inclose 

 areas showing changes in temperature of more than 10 degrees. 

 The narrow lines generally run in oval or circular form, indi- 

 cating (as will be shown subsequently) that atmospheric dis- 

 turbances move and operate in the form of great progressive 

 eddies ; that there are central points of intensit}^ from which 

 the force of the disturbance diminishes in all directions. 



A second clerk constructs a chart showing the change that 

 has occurred in the barometer during the past 24 hours. As in 

 the construction of the temperature chart, broad, heavy lines of 

 red separate the regions of rising barometer from those of falling 

 barometer. Narrow lines inclose the areas over which the 

 change in barometer has been greater than one-tenth, and so on. 

 Here, for instance, throughout a great expanse of territory, 

 all the barometers are rising— that is to say, the air cools, con- 

 tracts, becomes denser, and j^resses with greater force upon the 



