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Doc. 200.) 571
REPLY TO CELSIUS.
putation of the declination of the magnet with an accurate
observation which he made at Upsal on July 28, 1740, I ex
press to him my sincere thanks for the real service which he
has rendered to me : for in order that a computation based
upon theory may be established, it must be proved by observ
ation. I desire, however, first of all to have the honour of
stating that in my Opera Philosophica et Mineralia, which was
printed in Leipzig in 1734, no declinations had been submitted
to computation except a few for the meridian of London, and
a few more for that of Paris, including also a few for Rome,
Uranieburg, the Cape of Good Hope, &c.; among these ex
amples, however, there has not been a single one for the
latitude and longitude of Upsal. Professor Celsius, therefore,
requested Magister Hiorter to institute a computation at the
above-named place and time, according to the principles laid
down by me, which has resulted in 17 degrees, and 2; minutes,
while the observation exhibits only 8 degrees, 49 minutes, so
that my computation was found to be erroneous by 8 degrees,
13. minutes. In order, however, to show to whom this fault
ought to be attributed, I feel induced to submit my own com
putation ; where I have been compelled to make use of the same
Latin phraseology which I employed throughout the whole work,
so that it may plainly appear, that I have not deviated a hair’s
breadth from my former series of computations, and the rules
I then laid down.
The latitude of Upsal is 590 108° 20’—90°=18° 20’ ; now
50’. follows the operation by the
The eastern longitude from logarithms:
London is 15º. Sine 22° 30’ = 958284
1. Between 1720 and 1740 Sine 18 ° 20’ = 949756
intervene 20 years, which are Sine 6° 55’ =908051.
to be multiplied by 56. Thus 4. Multiplication must be
20° 56’=18° 40 ’. made for the south angle :
2. Subtract 18° 40’ from 20° x 20’=6° 40’.
112°, and from 15°, or: 5. These 6° 40’ are to be
112° + 15 ° - 18° 40 ’ = 108 ° 20’. subtracted from the south
3. For (p a), see figures in angle of London, and 15° are
the work itself. to be added, viz :
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