and 80 degrees 40' west long. from Paris) only
211;while at Lima (12 degrees 2' south lat.) the number rose to 219. I
found, in the years intervening between 1799 and 1803, that the whole force,
if we assume it at 1.0000 on the magnetic equator in the Peruvian Andes,
between Micuipampa and Caxamarca, may be expressed at Paris by 1.3482, in
Mexico by 1.3155, in San Carlos del Rio Negro by 1.0480, and in Lima by
1.0773. When I developed this law of the variable intensity of terrestrial
magnetic force, and supported it by the numerical value of observations
instituted in 104 different places, in a Memoir read before the Paris
Institute on the 26th Frimaire, An. XIII. (of which the mathematical portion
was contributed by M. Biot), the facts were regarded as altogether new. It
was only after the reading of the paper, as Biot expressly states
(Lametherie, 'Journal de Physique', t. lix., p. 446, note 2) and as I have
repeated in 'the Relation Historique', t. i., p. 262, note 1, that M. de
Rossel communicated to Biot his oscillation experiments made six years
earlier (between 1791 and 1794) in Van Diemen's Land, in Java, and in
Amboyna. These experiments gave evidence of the same law of decreasing
force in the Indian Archipelago. It must, I think be supposed, that this
excellent man, when he wrote his work, was not aware of the regularity of
the augmentation and diminution of the intensity as before the reading of my
paper he never mentioned this (certainly not unimportant) physical law to
any of our mutual friends, La Place, Delambre, Prony, or Biot.
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