348 THE NEW AGRICULTURE. 



temperature, the wind velocity, the amount of rainfall, the 

 appearance of the sky, the movement of the upper and lower 

 clouds, etc. Within 25 minutes the reports have all been 

 received, tabulated and corrected, and the results mapped out 

 upon the chart. The areas of low barometric pressure indi- 

 cate the storm center; the high, that of the cold wave. The 

 region of rainfall during the preceding twelve hours is in- 

 dicated, together with the temperature, and the appearance 

 of the sky. It is thus that the forecast official gets a view as 

 broad as the national domain of the weather conditions as 

 they existed but an hour before, and all the changes which took 

 place during the preceding twelve hours. 



From the various conditions existing and from his knowl- 

 edge of the phenomena concerned, the forecaster is able to 

 deduce many things the movement of the atmosphere for 

 example, together with the temperature which it will bring to 

 any given locality. He knows that the atmosphere under the 

 influence of gravity presses downward and outward in all 

 directions and flows, therefore, from the area of greatest 

 pressure marked "high" on the map towards that of least 

 pressure marked "low," and that the velocity of the wind de- 

 pends largely upon this difference, which is indicated by the 

 barometer. If, for illustration, the instrument reads 29.5 at 

 Chicago and 30.5 at Bismarck, N. Dakota, the difference of an 

 inch in the barometric column, indicating that degree of addi- 

 tional pressure at Bismarck, would cause the air to move 

 towards Chicago at the rate of 50 miles an hour, making all 

 allowance for the retardation caused by the friction and ob- 

 struction of the ground over which it passed. It is thus seen 

 that the forecasting of conditions as done by the officials of 

 the Weather Bureau is strictly scientific in its nature. Self- 



