WEATHER BUREAU. 5 1 



of stations of other countries, deductions may be drawn bearing 

 on the relative fitness of different localities for the support of 

 animal and vegetable life, physical geography and sanitary 

 science. 



Secondly, meteorology may be treated as the science of 

 weather ; that is, the changes which are from time to time taking 

 place in the physical condition of the atmosphere, and the effects 

 produced by such changes. 



These effects find expression in the temperature of the air, 

 its direction and motion, the amount of moisture it contains and 

 the balancing of the antagonistic forces of evaporation and con- 

 densation. 



Thirdly, we have the highest object of meteorology if we con- 

 sider it as a department of cosmical physics ; the investigation 

 of the physical conditions of the atmosphere and their relation 

 to the forces of light, heat, electricity and magnetism. All con- 

 ditions and phenomena of the atmosphere are illustrations of 

 the principles of physics. The properties of gases and vapors, 

 and the laws of heat and motion are here exemplified on a scale 

 vastly larger than that usually considered in laboratory experi- 

 ments, but the difference of the scale does not in any way affect 

 the application of physical law. 



The atmosphere is a gaseous envelope which surrounds the 

 earth ; it profoundly influences animal and vegetable life ; modi- 

 fies and retains the heat derived from the sun ; facilitates the 

 transmission of sound ; causes twilight, or the gradual shading 

 of night into day, and is intimately connected in the production 

 of weather phenomena and geological changes of all kinds. It 

 is endowed with the qualities of elasticity, and great sensitiveness 

 to the effects of heat. The height of the atmosphere is variously 

 computed to be from forty-five to sixty miles, but investigations 

 upon the duration of twilight show that its refractory power 

 extends possibly two hundred miles ; yet it is quite probable that 

 the weather conditions of rain and storms and cloudiness all 

 occur within eight miles of the surface of the earth. Indeed, 

 some of our more recent investigators hold that all these dis- 

 turbances in the atmosphere do not reach an elevation exceeding 

 two miles. 



The United States was the fourth government to establish a 

 permanent weather service, although its scientists were pioneers 



