DISCOVERY BY MEANS OF NEW MODES OF OBSERVATION. 575 



often the case, that effects, when first obtained, are so 

 extremely feeble that they can hardly be perceived at all. 

 The movements of the magnetic needle, for instance, 

 which revealed the existence of magnetic storms over 

 large portions of the earth, were many of them so small 

 as to be microscopically minute, and required the most 

 acute observation in order to detect them. 



d. By the combined action of many observers. A 

 large amount of discovery in astronomical, magnetical, 

 and meteorological science, and the subject of cosmical 

 spectrum analysis, has resulted from the combined intel- 

 lectual action of many observers in different parts of the 

 world. In consequence of the advice of M. Humboldt, 

 the Imperial Academy of Russia, about the year 1830, 

 established a chain of magnetic stations right across 

 the entire Russian Empire ; at Petersburg, Moscow, Hel- 

 singfors in Finland, Catherinburg, Kasan, Barnaoul, and 

 Nertschinsk in Siberia, Sitka in Russian America, and 

 even in Pekin. In the year 1835, similar stations were 

 erected all over Germany ; also at Stockholm, Copenhagen, 

 Upsala, Milan, Munich, Dublin, and Greenwich ; and at 

 these places simultaneous observations of the three mag- 

 netic elements of intensity, declination and inclination, 

 were taken six times in each year, at intervals of five 

 minutes each, during twenty-four hours. Subsequently, 

 also, stations were formed at Toronto, St. Helena, the Cape 

 of Good Hope, Van Diemen's Land, Bombay, Simla, Singa- 

 pore, and at Kelso in Scotland ; and afterwards at Brussels, 

 Prague, Algiers, Cadiz, Cairo, Lucknow, Travancore, and 

 at Philadelphia and Cambridge, U.S. America ; and the 

 reduction and comparison of the observations made at all 

 these places have resulted in the discovery of a large amount 

 of valuable knowledge respecting terrestrial magnetism. 



