5 degrees. (See my 'Relat. Hist.', t. iii.,
p. 622.) At Guarmey (10 degrees 4' south lat.), Huaura (11 degrees 3' south
lat.), and Chancay (11 degrees 4' south lat.), Huaura (11 degrees 3' south
lat.), and Chancay (11 degrees 32' south lat.), the inclinations are 6.80
degrees, 9 degrees, and 10.35 degrees of the centesimal division. The
determination of position by means of the magnetic inclination has this
remarkable feature connected with it, that where the ship's course cuts the
isoclinalline almost perpendicularly, it is the only one that is independent
of all determination of time, and consequently, of observations of the sun
or stars. It is only lately that I discovered, for the first time, that as
early as at the close of the sixteenth century, and consequently hardly
twenty years after Robert Norman had invented the inclinatorium, William
Gilbert, in his great work, 'De Magnete', proposed to determine the latitude
by the inclination of the magnetic needle. Gilbert ('Physiologia Nova de
Magnete', lib. v., cap. 8, p. 200) commends the method as applicable "a?‘re
caliginoso." Edward Wright, in the introduction which he added to his
master's great work, describes this proposal as "worth much gold." As he
fell into the same error with Gilbert, of presuming that the isoclinal lines
coincided with the geographical parallel circles, and that the magnetic and
geographical equators were identical, he did not perceive that the proposed
method had only a local and very limited application.
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