1 84 Instructions for the Scientific Expedition 



To pursue this plienomenon successfully, and to promote in other 

 directions the theory of terrestrial magnetism, it was necessary to 

 extend and vary the stations of observation, and to adopt at all a 

 common plan. Such a system of simultaneous observations was or- 

 ganized by Von Humboldt in the year 1827. Magnetic stations were 

 established at Berlin and Freyberg : and the Imperial Academy of 

 Russia entering with zeal into the project, the chain of stations was 

 carried over the whole of that colossal emi)ire. Magnetic houses 

 were erected at Petersburg and at Cazau ; and magnetic instru- 

 ments were placed, and regular observations commenced, at Moscow, 

 at Sitka, at Nicolajelf in the Crimea, at Barnaoul and Nertschinsk 

 in Siberia, and even at Pekin. The plan of observation was definitely 

 organized in 1 830 ; and simultaneous observations were made seven 

 times in the year, at intervals of an hour for the space of forty-four 

 hours. 



In 1834 the illustrious Gauss turned his attention to the subject 

 of terrestrial magnetism ; and having contrived instruments which 

 were capable of yielding results of an accuracy before unthought of 

 in magnetic researches, he proceeded to inquire into the simulta- 

 neous movements of the horizontal needle at distant places. At the 

 very outset of his inquiry he discovered the fact, that the synchronism 

 of the perturbations was not confined (as had been hitherto imagined) 

 to the larger and extraordinary changes ; but that even the minutest 

 deviation at one place of observation had its counterpart at the other. 

 Gauss was thus led to organize a plan of simultaneous observations, 

 not at intervals of an hour, but at the short intervals of five mi- 

 nutes. These were carried on through twentjT^-four hours six* times 

 in the year ; and magnetic stations taking part in the system were 

 established at Altona, Augsburg, Berlin, Bonn, Brunswick, Breda, 

 Breslau, Cassel, Copenhagen, Dublin, Freyberg, Gottingen, Green- 

 wich, Halle, Kazan, Cracow, Leipsic, Milan, Marburg, Munich, 

 Naples, St. Petersburg, and Upsala. 



Extensive as this plan appears, there is much yet remaining to be 

 accomplished. The stations, numerous as they are, embrace but a 

 small portion of the earth's surface ; and what is of yet more im- 

 portance, none of them are situated in the neighbourhood of those 

 singular points or curves on the earth's surface, where the magni- 

 tude of the changes may be expected to be excessive, and perhaps 

 even their direction inverted. In short, a wider system of observa- 

 tion is required to determine whether the amount of the changes 

 (which is found to be very diflferent in different places) is dependent 

 simply on the geographical or on the magnetic co-ordinates of the 

 place ; whether, in fact, the variation iu that amount be due to 

 the greater or less distance of a disturbing centre, or to tlie modifying 

 effect of the mean magnetic force of the place, or to both causes 

 acting conjointly. In another respect also, the plan of the simul- 

 taneous observations admits of a greater extension. Until lately the 

 movements obsei"ved have been only those of the magnetic declination, 

 although there can be no doubt that the inclination and the intensity 



* Recently reduced iofour. 



