of Terrestrial Magnetism. 47 



obtain observations in the interior of Mexico, where the soil 

 is elevated six thousand feet above the level of the sea. Lastly, 

 during my last residence in Paris, I had the honour of pro- 

 posing to Admiral Duperre, Minister for marine affairs, the 

 establishment of a magnetic station in Iceland. The pro- 

 posal was received with the utmost eagerness, and the instru- 

 ment, which is already ordered, will be deposited during the 

 present summer at the port of Reikiawig, when the expedi- 

 tion which has been sent to the north in search of M. de Blosse- 

 ville and his companions in misfortune returns to Iceland to 

 continue its scientific labours. There cannot be any doubt 

 that the Danish Government, which protects with generous 

 ardour astronomy and the advancement of nautical science, 

 will favour the establishment of a magnetic station in one of 

 its provinces bordering on the polar circle. At Chili also 

 M. Gay has made a great number of corresponding horary 

 observations, according to the instructions of M. Arago. 



I have entered upon this long and minute historical detail, 

 to show how far I have hitherto succeeded, in conjunction with 

 my friends, in extending the number of simultaneous observa- 

 tions. After my return from Siberia, Mr. Dove and I pub- 

 lished, in 1830, a graphic delineation of the curves of horary 

 declination of Berlin, Freiberg, Petersburgh, and Nicolajeff 

 in the Crimea, to show the parallelism of these lines, notwith- 

 standing the distance of the stations and the influence of ex- 

 traordinary perturbations. In the comparison of the observa- 

 tions of Si. Petersburgh and Nicolajeff, use has been made 

 of observations taken at the very small intervals of twenty mi- 

 nutes. It must not, however, be imagined that this parallelism 

 of inflections always exists in the horary curves. We have 

 found that even in places very near to each other, — for instance, 

 at Berlin and in the mines of Freiberg, — the magnetic reac- 

 tions from the interior to the surface of the earth are not al- 

 ways simultaneous ; that one of the needles presents consider- 

 able perturbations, while the other preserves that regularity, 

 which under each meridian is the function of the true time of 

 the place. In the memoir published in 1S30, I proposed the fol- 

 lowing periods for simultaneous observations at all the stations. 



March 20th and 21st. 1 

 May 4th and 5th. 

 June 21st and 22nd 

 Aug. 6th and 7th 



From four o'clock in the morning of 

 the first day, to midnight of the se- 

 cond day. The observations to be 

 )> continued at each magnetic station 

 Sept. 23rd and 24tli. I during the day and night, at inter- 

 Nov. 5th and 6th. | vals not exceeding one hour. 



Dec. 21st and 22nd. J 



As several observers situated upon the line of the stations 



