TRANSACTIONS OF THE SECTIONS. 27 



the utmost limits of Europe, and to hold at stations as remote as Dublin, Petersburg, 

 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. This question was determined by the very first results of 

 the observations recently established by the British Government ; and the observa- 

 tions now laid before the Section were selected as elucidating it in a very marked 

 manner. These observations were those of the declination and horizontal magnetic 

 intensity observed at Brussels, Milan, Prague, Toronto, and St. Helena, on the 29th 

 of May 1840 ; and at Dubhn, Toronto, St. Helena, and Van Diemen's Land, on the 

 29th of August of the same year. The magnetical disturbances which occurred on 

 these days were among the most considerable which had been as yet observed. On 

 the former days the declination at Toronto underwent a sudden change, amounting 

 to 1° 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, 

 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 -sVth part of the whole intensity ; while at Dublin the change was 

 even greater, and extended beyond the scale of the instrument. It is probable that 

 an attentive comparison of the curves may lead to many important results ; but 

 there are some which appear upon a cursory inspection, which Mr. Lloyd said that 

 he should now notice. The first of these was, that the greater magnetic disturbances 

 appeared to be synchronous at the most distant stations. This important fact is ex- 

 hibited 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 re- 

 presentative curves exhibiting none of that similarity already referred to, which was 

 shown within the limits of Europe, and the epochs of the successive 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 Professor Bache 

 at Philadelphia, and by himself at Dublin, in November 1839, in the hope of deter- 

 mining differences of longitude by means of the corresponding movements of the 

 magnet at the two stations. The changes observed in the observations at present 

 under consideration were, however, far greater in magnitude, and placed the pheeno- 

 menon in a much stronger light. The last circumstance to which Mr. Lloyd invited 

 the attention of the Section was, that the curves of horizontal intensity presented a 

 much nearer agreement at remote stations than those of declination ; from which it 

 may be inferred, that a true knowledge of the nature and laws of the disturbing 

 causes will be better attained by the examination of intensity changes (including, of 

 course, those of the vertical intensity) than of those which are dependent solely on 

 the direction of the acting forces. There were many other points of minor interest 

 suggested by the examination of these curves ; such as the appearance of a correspond- 

 ence in some of the minuter changes at all the stations, although the resemblance in 

 the greater changes was obliterated. If this should prove to be anything more than 

 a mere fortuitous coincidence, the result might be expected to lead to some important 

 conclusions with regard to the acting forces. 



Professor Lloyd then laid upon the table the curves representing the changes of 

 magnetic declination, observed at Cambridge University (Massachusetts) by Mr. W. C. 

 Bond, on the term-days of May and October 1840. The corresponding observations 

 made at the magnetical observatory at Toronto, by Lieut. Riddell, were laid down 

 in a curve, in connexion with the latter. The results exhibited the same close agree- 

 ment in the forms of the curves, and in the epochs of the successive maxima and 

 minima, as had been already noticed in Europe, although (as before remarked) all 

 resemblance between these and the European system of changes is nearly obliterated. 

 New Cambridge is distant about 500 miles from Toronto ; the mean declination there 



is 9° 20' west. 



On Sea Coonpasses. By the Rev. T. Dury. 



In this communication Mr. Dury stated some of the results to which the Rev. 

 Dr. Scoresby, in the continuation of his magnetical researches, has arrived, and 



