38 REPORT OF THE SECRETARY. 



direction. The preceding sketch gives a general explanation of the 

 marked contrast between the rain-fall of the eastern and western halves 

 of the United States. 



Most of the records of meteorological phenomena which were made 

 previous to a comparatively late date had for their object the determin- 

 ation of, what may be called, the statical condition of the weather in dif- 

 ferent places, or, in other words, the determination of the average atmo- 

 spheric pressure, temperature, direction of the wind, and the fall of rain. 

 A knowledge of these elements is of great importance in ascertaining the 

 relative climates of different countries, particularly in regard to sanit.ary 

 and agricultural considerations. In later years, however, systems of 

 meteorology have been established having more especially for their ob- 

 ject the record of the simultaneous conditions of the atmosphere in differ- 

 ent portions of the earth, and the origin and progress of storms ; that is, 

 to discover, if possible, the dynamic principles which regulate the phe- 

 nomena of the weather. Systems of this kind have been established in 

 almost every part of Europe and in several parts of Asia, even in Turkey, 

 in the East Indies, and in North America. These systems are not only 

 intended to indicate the laws according to which the atmospheric dis- 

 turbances are produced, but, also, to predict, by the aid of the telegraph, 

 the weather that may be expected within a given time. 



The Smithsonian Institution was the first to make use of the tele- 

 graph for this purpose. The state of the barometer and thermometer 

 and the direction of the wind were received from the various telegraphic 

 stations at 8 o'clock each morning and recorded on a large map fastened 

 to a board, into which small iron pins were driven to support circular 

 cards of different colors, which indicated the character of the sky and 

 of the weather — whether cloudy or clear, raining or snowing. On each 

 card was drawn an arrow, the direction of which could be varied by 

 suspending the card from one of eight holes with which it was pierced. 

 A glance at this map showed at once the condition of the sky and direc- 

 tion of the wind over the whole country, and knowing from previous 

 observation the direction of the movement of storms, the weather could, 

 in most cases, be predicted, frequently more than a day in advance. 

 In Europe the prediction of the weather is founded on the probable 

 direction of the wind at a given place as deduced from, telegrams 

 giving the maximum and minimum pressures of the air as indicated 

 by the barometer. It has been found from observation that the 

 wind which may be expected will blow nearly at right angles to a line 

 joining the maximum and minimum pressure of the air, and that the 

 face being turned toward the minimum point, the wind will come from 

 the left-hand side. This rule, however, may be theoretically deduced 

 from the movement of the air in the form of a cyclone, but will scarcely 

 hold true in case of the storms observed in the eastern portions of the 

 United States. The storms that visit the west of Europe are those 

 which come directly from the ocean, where the cyclonal character of the 



