IX NOTES. 



regarde la loi du decroissement des forces magnetiques, du pole a 1'equateur, 

 comme le resultat le plus important de mon voyage americam." It is not 

 certain, but it is very probable, that Condorcet read Lamanon's letter of July, 

 1787, at a meeting of the Academy of Sciences at Paris ; and I regard such 

 reading as a sufficient act of publication (Anauaire du Bureau des Longitudes, 

 1842, p. 463). The first recognition of the law belongs, therefore, indis- 

 putably, to the companion of La Perouse ; but, long unheeded or forgotten, it 

 appears to me that the knowledge of the law of the variation of the magnetic 

 force with the latitude only obtained a real scientific existence by the publication 

 of my observations of 1798 1804. The object and the length of this note 

 will not be surprising to those who are familiar with the recent history of 

 magnetism, and the doubts excited by it, and who know, from their own 

 experience, that one attaches some value to that which has formed a subject 

 of constant occupation during five years of laborious research in tropical 

 climates, and in dangerous mountain journeys. 



( 16 ) p. 175. The greatest intensity of the magnetic force hitherto observed 

 on the surface of the Earth is 2,071, and the least, 0,706. Both are in the 

 southern hemisphere : the geographical position of the first is, lat. 60 19' S M 

 long. 131 20' E. from Greenwich, observed by Sir James Ross, where the in- 

 clination was 83 31', (Sabine, Contributions to Terrestrial Magnetism, No. V. 

 Phil. Trans. 1843, p. 231). The minimum was observed by Erman in 

 20 00' S., and 324 57' E. from Greenwich, (Ermaii, Phys. Beob. 1841, 

 S. 570), at which point the inclination was 7 56'. These values of the force 

 are in the ratio to each other of 1 to 2'933. It was long supposed that the 

 ratio of the greatest to the least intensity of the force on the surface of the 

 Earth was as 2 to 1 (Sabine, Report on Magnetic Intensity, p. 82). 



[This note is slightly altered from the original, with M. de Humboldt's 

 concurrence, in order to bring it into more exact accordance with the facts. 

 EDITOR] . 



( 161 ) p. 176. Speaking of amber (sucdmim, glessum,) Pliny says, xxxvii. 

 8, " Genera ejus plura. Attritu digitorum accepta caloris anima trahunt in 

 se paleas ac folia arida quse levia sunt, ac ut magues lapis ferri ramenta 

 quoque." Plato, in Timseo, p. 80 ; Martin, Etudes sur le Time'e, T. ii. pp. 

 343346 ; Strabo, xv. p. 703, Casaub, ; Clemens Alex. Strom, ii. p. 370, 

 .where a singular distinction is made between rb crovxtov and TO eAeirrpoi/). 

 If Thales, in Aristot. de anima, 1, 2, and Hippias, in Diog. Laertio, 1, 24, 

 ascribe to the magnet aud to amber a spirit, it is obvious that the word i 

 meant simply to express a force or a cause of motion. 



