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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, Ist, 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 
3lst 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 11 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 
