The southern boundary of the Tropical Zone is—
the rhumb line from the Port of Santos, Brazil, to the point
where the meridian of longitude 40°W intersects the Tropic of
Capricorn; thence the Tropic of Capricorn to the west coast of Africa;
from the east coast of Africa the parallel of latitude 20°S to
the west coast of Madagascar, thence the west and north coasts of
Madagascar to longitude 50°E, thence the meridian of longitude
50°E to latitude 10°S, thence the parallel of latitude 10°S
to longitude 98°E, thence the rhumb line to Port Darwin, Australia,
thence the coasts of Australia and Wessel Island eastwards to Cape
Wessel, thence the parallel of latitude 11°S to the west side
of Cape York; from the east side of Cape York the parallel of latitude
11°S to longitude 150°W, thence the rhumb line to the point
latitude 26°S, longitude 75°W, thence the rhumb line to the
point latitude 32°47’S, longitude 72°W, and thence to
the parallel of latitude 32°47’S to the west coast of South
America.
Valparaiso and Santos are to be considered as
being on the boundary line of the Tropical and Summer Zones.