-1859] WRITINGS OF JOSEPH HENRY. 23 



through nine years. The number of separate observations 

 amounted to nearly six millions, which required at least as 

 much labor for their reduction as that expended in the ob- 

 servations themselves. The comparisons of these observa- 

 tions are still in progress, and will occupy the attention of 

 the student of magnetism and meteorology for many 3'cars 

 to come. The system was established more particularly to 

 study the changes of the magnetic needle, and on this sub 

 ject alone it has afforded information of sufficient impor- 

 tance to repay all the labor and time expended on it. It 

 has shown that the magnetic force is scarcely constant from 

 one moment to another, that the needle is almost incessantly 

 in motion, that it is affected by the position of the sun and 

 moon, and by perturbations, connected with meteorological 

 phenomena, of a most extraordinary character. 



In regard to meteorology, this system furnished reliable 

 data for the great movements of the atmosphere, and the 

 changes in its thermal and hygrometric condition. But to 

 obtain a more minute knowledge of the special climatology 

 of different countries, it is necessary that a series of observa- 

 tions, at a great many places, should be continued through 

 a number of years, and at stated periods of the day — not as 

 frequent as those of the observations we have mentioned, 

 but embracing as many elements, and even adding to these, 

 as new facts may be developed or new views entertained. 

 In many countries accordingly, provision has been made by 

 their respective governments, for continued though local sys- 

 tems -of this kind. The Government of Prussia appears to 

 have taken the lead in this important labor, and its example 

 has been followed by those of Great Britain, Russia, Austria, 

 Bavaria, Belgium, Holland, and France. In these coun- 

 tries, regular and continuous observations are made with 

 reliable instruments, on well-digested plans. 



Though the Government of the United States took no part 

 with the other nations of the earth in the great system be- 

 fore described, yet it has established and supported for a 

 number of years a partial system of observation at the dif- 

 ferent military posts of the army. Among other duties 



