vii., p. 320); but, notwithstanding the most careful search, they are not
now to be found. From a copy of a very important letter of Lamanon, now in
the possession of Captain Duperrey, which was addressed to the then
perpetual secretary of the Academy of Sciences, but was omitted in the
narrative of the 'Voyage de La Perouse', it is stated "that the attractive
force of the magnet is less in the tropics than when we approach the poles,
and that the magnetic intensity deduced from the number of oscillations of
the needle of the inclination-compass varies and increases with the
latitude." If the Academicians, while they continued to expect the return
of the unfortunate La Perouse, had felt themselves justified, in the course
of 1787, in publishing a truth which had been independently discovered by no
less than three different travelers, the theory of terrestrial magnetism
would have been extended by the knowledge of a new class of observations,
dating eighteen years earlier than they now do. This simple statement of
facts may probably justify the observations contained in the third volume of
my 'Relation Historique' p. 615): "The observations on the variation of
terrestrial magnetism, to which I have devoted myself for thirty-two years,
by means of instruments which admit of comparison with one another, in
America, Europe, and Asia, embrace an area extending over 188 degrees of
longitude, from the frontier of Chinese Dzoungarie to the west of the South
Sea bathing the coasts of Mexico and Peru, and reaching from 60 degrees
north lat.
Pages:
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392