MDDM18: Something Underground, Moving Westward ...

[Dave Monroe]

"'These Data arriv'd but this Instant, by the German
Packet,-- the latest Declination Figures.  Our
easterly movement, in Pennsylvania, as it's been doing
in latter Years, decelerates, yet,-- here, 'tis four
point five minutes east,' as Dixon attentivel gazes
over her shoulder, 'when in the year 'sixty, 'twas
four point six.  If you head South, 'twill be three
point nine at Baltimore.'
   "'Were these measur'd Heights,' her murmurs, 'a
very Precipice.'
   "'What Could be causing it, do you imagine?'
   "'Something underground, moving Westward...?'"
   "'Hush.'  Her Eyes rapidly sweep the Vicinity.  'No
one ever speaks of that aloud here,-- what sort of
incautious Lad are you, exactly?'" (M&D, Ch. 30, p.
299)

Main Entry: dec·li·na·tion 
Pronunciation: "de-kl&-'nA-sh&n
Function: noun
Etymology: Middle English declinacioun, from Middle
French declination, from Latin declination-,
declinatio angle of the heavens, turning aside
Date: 14th century

[...]

6 : the angle formed between a magnetic needle and the
geographical meridian

http://m-w.com/cgi-bin/dictionary

Colonialism, Imperialism, Eurocentrism, later,
Manifest Destiny, what have you here, yes yes yes, at
any rate, foreboding, sinister, even, but ...

>From Patricia Fara, Sympathetic Attractions: Magnetic
Practices, Beliefs, and Symbolsim in
Eighteenth-Century England (Princeton, NJ: Princeton
UP, 1996), Ch. 3, "The Direction of Invention: Setting
a New Course for Compasses," pp. 66-90 ...

"England's naval strength was vital for protection
against rival European powers for increasing her
trade, and for defending and acquiring overseas
territory.  But seafaring still seemed extremely
dangerous.  Johnson quipped that 'being in a ship is
being in a jail, with the chance of being drowned' ...
   "Entrepreneurial natural philosophers recognized
that inventions improving naval safety promised a
double reward of money and prestige.... John
Harrison's chronometer ... John Hadley's quadrant ...
   "... the Board of Longitude ..." (p. 66)

   "Several projectors submitted magnetic schemes for
approval ....  They mostly relied on long-established
observations indicating that the earth's magnetic
power varies both spatially and temporally.  Natural
philosophers trying to establish a regular pattern for
these fluctuations used two measures of terrestrial
magnetism, the variation and the dip.  The variation
at any particular place and time was the angle between
geographic North and the direction a compass needle
was pointing.  The dip, discovered later and
experimentally far harder to ascertain relaibly, was
the angle between the horizontal and a magnetic needle
free to rotate in a vertical meridional plane. 
Mariners had acknowledged the problems presented by
variation at least since the time of Christopher
Columbus.  They realized that the value of compasses
and charts was limited, since they did not know
exactly where a compass needle was pointing: its
precise orientation depended on the ship's location on
the surface of the terraqueous globe...." (p. 67)

And here skipping ahead to Ch. 4, "An Attractive
Empire: Mapping Terrestrial Magnetism," pp. 91-117 ...

"During the eighteenth century, numerous polemicists
called for more systematic global projects to compile
magnetic information....  However, no administrative
framework existed for superintending and financing
such investigations.  Colective ventures sounded
appealing, but conflicting political and commercial
interests impeded colaboration.  Mounting a research
expedition depended largely on personal initiative,
although the Royal Society played a key role in
facilitating financial support.  It was not until the
nineteenth century that European governments and
scientific societies found international copperation
mutually advantageous.
   "European  communities of natural philosophers
developed an increasingly formalized network of
communication.  They launched several major projects,
most famously the two expeditions to measure the
transit of venus.  Viewing themselves as enlightened
members of an international Republic of Letters, some
experimenters freely exchanged magnetic information
...." (p. 101)

"Natural philosophers compiled an accumulating fund of
magnetic observations and developed new ways of
representing terrestrial magnetism.  At the end of the
seventeenth century, international measurements were
mainly collected by maritime voyagers.  But as
metropolitan investigators miniaturized the world into
their notebooks, they transformed the chaos of life at
sea into an orderly rendition of magnetic nature. 
They demonstrated their intellectual possession of
terrestrial magnetism by translating the overseas
readings of itinerant observers into a convenient
format for stationary experimenters.  By converting
the global vagaries of magnetic variation into a
two-dimensional inscription, they stabilized the
constantly fluctuating magnetic patterns into a fixed
representation.  The demystified the world's magnetic
behavior by capturing it in black and white on a piece
of paper." (pp. 105-6)

"... gradually they came to present their observations
in tables ....  Like maps, tables can embody
investigators' classificatory systems for structuring
their world.... as natural philosophers constructed a
new magnetic science, they converted traditional" (p.
106)

"By focusing exclusively on the data, the observer's
shipboard life has been erased, and the earth's
characteristics seem objectively displayed.  However,
the recorded values of the variation increase
suspiciously regularly, suggesting that the reading
were rounded off to comply with an assumed regularity.
 Such tables enabled natural philosophers to
demonstrate how they disciplined maritime confusion
into an orderly world goverend by natural laws." (pp.
106-7)

   "In England during the eighteenth century, two
important English global magnetic charts were
produced, bith in several versions: Halley's and
Mountaine and Dodson's.  Although their makers claimed
that they had been derived empirically, they were
affecetd by theoretical considerations.  Mapping the
emasurements of terrestrial magnetism entailed solving
probability problems similar to those involved in
analyzing population data: how to derive a
representative average with a great number of
observations; and how to cope with gaps in the records
or with readings disobeying a general pattern.  Halley
and Dodson were both involved in commercial and
political projects using mortality figures to
calculate appropriate insurance premiums.  Enmeshed in
the London culture of projectors, maritime insurers,
and government financiers, they developed techniques
for coping with large disorderly sets of figures. 
When they compiled their magnetic charts, they used
similar tactics to persuade their data to demonstrate
their ideas.
   "Halley was world-famous for his innovative maps
..." (p. 108)

"Swift later articulated contemporary skepticism about
traditional maps:

   So Geographers in Afric-maps,
   With Savage-Pictures fill their Gaps;
   And o'er uninhabitable Downs
   Place Elephants for want of Towns.

"But Halley had already given his chart a modern
authority by dropping the old-fashioned rhumb lines
and eliminating the pictorial cartouches...." (p. 110)

And see here ...

http://usm.maine.edu/maps/exhibit8/17.jpeg

http://usm.maine.edu/maps/exhibit8/nrcomp.html

By the way, appropo of nothing immediately at hand ...

   "People living in the eighteenth century did not
draw the modern distinction between animate and
nonanimate matters.  They adhered to older Neoplatonic
and Aristotelian interpretations of the natural world
as a fixed continuous hierarchy linking human beings
downwards through simple animals and plants to stones
...." (Ch. 5, "Measuring Power: Patterns in
Experimental Natural Philosophy," p. 138)

But see as well, on magnetic variation ...

http://www.nmm.ac.uk/education/fact_files/fact_compass.html

http://www.geo-orbit.org/sizepgs/magmapsp.html

http://www.geolab.nrcan.gc.ca/geomag/e_magdec.html

http://www.ngdc.noaa.gov/cgi-bin/seg/gmag/fldsnth1.pl

http://www.comanco.com/Magvar/magvar.html

Okay, some loose ends later today/early tomorrow. 
Thanks to all for yr continued patience ...

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