156 Proceedings of the British Association. 



other in all their inflexions, and differing only in the magnitude 

 of the change. This similarity had been found to extend to the 

 utmost limits of Europe, and to hold at stations as remote as Dub- 

 lin, Petersburghj and Milan. It became, therefore, a question of 

 great interest in the extension of this system to still more distant 

 stations, to determine whether there were any and what limits 

 to this accordance. The question was determined by the very 

 first results of the observations recently established by the British 

 government, and the observations first mentioned, were selected 

 as elucidating it in a very marked manner. The magnetical dis- 

 turbances which occurred on these days were among the most 

 considerable which had been as yet observed. On the former 

 day, (May 29, 1840,) the declination at Toronto underwent a 

 sudden change, amounting to L° 52' in about twenty minutes of 

 time, while the disturbance of the horizontal force was so great 

 as to carry the magnet beyond the limits of its scale. On the 

 latter day, (Aug. 29, 1840,) the greatest change'of the declination 

 amounted to 1° 26' at Toronto, and to 1° 18' at Dublin. The 

 greatest change of the horizontal intensity at the former station 

 amounted to .028, or about one thirty sixth part of the whole in- 

 tensity : while at Dublin the change was even greater, and ex- 

 tended beyond the scale of the instrument. It is probable that 

 an attentive comparison of the curves may lead to many impor- 

 tant results; but there are some which appear upon a cursory 

 inspection, which Mr. Lloyd said he should now notice. The 

 first was, that the greater magnetic disturbances appeared to be 

 synchronous at the most distant stations. This important fact 

 is exhibited much more evidently in the changes of horizontal 

 intensity than in those of declination, and if verified by further 

 comparisons, leads to the conclusion, that the principal forces 

 which disturb the magnetic equilibrium of the earth, are not of 

 local agency. The next circumstance which merited attention 

 was, that the order of the changes was no longer regulated by 

 the same law at very remote stations ; the representative curves 

 exhibiting none of that similarity already referred to, which was 

 shown within the limits of Europe, and the epochs of the suc- 

 cessive maxima and minima presenting no agreement whatever. 

 This important fact was first brought to light in the course of a 

 series of simultaneous observations, made by Prof Bache at Phil- 

 adelphia, and by himself at Dublin, in November, 1839, in the 



