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plained the system of combined observation carried on 

 under the auspices of that distinguished geometer, at so 

 many places in Europe, and now, through the instrumen- 

 tality of the Russian government, extended over the whole 

 of northern Asia, and reaching even unto China. The 

 results of this system hitherto obtained are, 1st, that the 

 direction of the terrestrial magnetic force (estimated in the 

 horizontal plane) is subject not only to a regular diurnal 

 change, whose maxima and minima return at fixed hours ; 

 but also to irregular perturbations, which succeed one 

 another with great rapidity, and which are not periodic. 

 2ndly. That these irregular movements of the horizontal 

 needle occur at the same instants of absolute time, and are 

 similar to one another, at the most distant places at which 

 observations have been hitherto made. This synchronism 

 in the movements of the needle, Mr. Lloyd observed, was 

 so exact, that with the instrumental means now placed at the 

 disposal of observers by M. Gauss, he had no doubt but that 

 a very close approximation might be made to the determina- 

 tion of geographical longitudes. 



Professor Lloyd then proceeded to lay before the 

 Academy the results of the observations made in Dublin 

 according to the methods described. The first series of such 

 observations was made every five minutes during the twenty- 

 four hours, commencing at noon (Gottingen time) on the 

 31st of August last. The observations were undertaken in 

 compliance with the general invitation of Baron Humboldt, 

 and on the occasion of the scientific expedition of M. Parrot 

 to the North Cape. The results are laid down in curves, 

 according to the usual method of graphical representation, 

 and exhibit a remarkable disturbance occurring between 8 

 and 1 1 p. m. (Gottingen time). The observations made at 

 the same time elsewhere are not yet published; but Mr. 

 Lloyd has, through the kindness of Baron Humboldt, 

 received a copy of the observations made at Berlin at the 



