of Terrestrial Magnetism. 387! 



at the same precise instants of time, on particular days, at dif- 

 ferent places. The magnetic observations at Gottingen became 

 the type of all establishments of this kind, and at all, the obser- 

 vations were made, for the sake of uniformity, in Gottingen time, 

 and with astronomical exactness. The first conclusions thus 

 obtained were very important. Amidst many irregularities very 

 general laws were perceived. The simultaneity of perturbations 

 at places considerably distant was confirmed, as well as the in- 

 fluence of auroras or northern lights, even at a distance, and the 

 influence of seasons and of different hours of the day. For 

 further particulars consult the memoir published by Gauss in 

 1836, and translated in the second volume of Taylor^s Scientific 

 Memoirs*. 



But thus far the inquiry had been comparatively restricted : 

 the vastness of the problem required a larger field, — the whole of 

 Europe, and still more the portion of it over which the magnetic 

 observatories extended, being very small as compared with the 

 entire globe. To study the problem adequately, it was- necessary 

 to determine accurately both the magnetic constants and their 

 variations at several distant parts of the earth^s surface : this 

 was beyond the power of scientific associations and required the 

 support of Governments. A first proposal of this nature had 

 been made to the Emperor of Russia by Humboldt with the sup- 

 port of the Petersburgh Academy in 1819, with such success that 

 magnetic establishments were formed in different parts of the 

 Russian Empire, and even as far as China. A still wider range 

 was however requisite ; and the same celebrated individual, aided 

 by the British Association for the Advancement of Science, and 

 by the Royal Society of London, applied to the English Govern- 

 ment as peculiarly interested in all that relates to navigation, 

 and as having within its own dominions points of the globe 

 which could furnish science with the desired information. The 

 request was met with the greatest alacrity, promptness and 

 liberality. 



Two complete magnetic observatories were immediately esta- 

 blished at Dublin and Greenwich, one under the direction of 

 Dr. Lloyd, the other under that of Mr. Airy. For the distant 

 stations four magnetical and meteorological observatories were 

 erected at points suggested by Humboldt, Herschel, Airy and 

 Sabine, as the best suited to disclose the laws of the phsenomena. 

 They were chosen so as to include great variety of magnetic in- 

 tensity, and opposite positions in respect to the magnetic poles 

 and to the magnetic and geographic equators. 



* The Scientific Memoirs referred to contain translations of several of 

 the most important memoirs on the subject of terrestrial magnetism, with 

 descriptions of the apparatuses and methods of Gauss and Weber. 



