Geoscience Reference
In-Depth Information
Fig. 18
If the Earth was drilled through with a tube in the shape of an elbow, filled with water
and with its corner at the center, the pressure of water along each arm of the tube would have
to be equal so that the pressure at the center was the same in both arms. Because the Earth is
rotating around the North Pole, the weight of water in the equatorial arm is reduced by cen-
trifugal force, so there has to be a greater length of tube to make the same pressure. Therefore
the Earth is flattened at the poles
People
James Pound (1669-1724)
Educated in the field of medicine, Pound took holy orders and was sent by the East India
Company to be chaplain in Madras and then Chushan Dao, an island near Shanghai.
He made astronomical observations while he traveled and sent them to John Flamsteed, the
astronomer royal. Flamsteed gave him a quadrant with which to measure the positions of
the southern stars, but unfortuneately it took four years to reach him and corroded on the
way. In 1702 Pound moved to Pulo Condore, an island in the Mekong delta, and when in
1705 native troops attacked the settlement and set fire to the buildings, Pound and ten other
Europeans escaped with just their lives.
Pound returned to England via Batavia and took up a quieter life as a vicar in Wanstead.
He used a 15-foot telescope in 1716 and 1717 to make various planetary observations and
in 1717 installed a 123-foot focal length lens that Huygens had made as the collecting lens
of an aerial telescope (one with no tube), supported on a maypole removed from a London
street by Isaac Newton. Newton used Pound's measurements of Jupiter, Saturn and their
satellites in the third edition of his
Principia
.
Pound went on to support the interest of his nephew James Bradley (1692-1762) in astron-
omy and to work with him in discovering the phenomenon of the aberration of light.
For Newton the shape of the Earth was important since it not only in itself pro-
vided a test of his theory of gravity but also affected his calculations of the motion
of the Moon and other applications of the theory. Newton therefore examined
