Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.1): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

GENERAL REMARKS. 527 alternate increase and decrease of dip. Commencing with the meridian of Greenwich, and proceeding eastwardly round the hemisphere, we may distinguish the divisions as follows, in the order of their geographical succession. 1*^ South dip increasing. annually, St.Helena.. .. 1 754 to 1775- • 6,9' Do 1775 to 1836.. 6,5 Cape of Good Hope 1751 to 1775.-7,2 To this division also belongs Ascension ; but as the north end of the needle dips at that island, the change is north dip diminishing, instead of south dip increasing. annually. Cape of GoodHope i775 to 1836. . 6,6- Mauritius .. .. 1754 to 1824. . 1,3 Do 182410 1836.. 0,8 Ascension Do. 1754 to 1775 1775 to 1836 6,3 annually. 7,2 Otaheite Lima and Callao Do. .. Valparaiso .. Concep9ion . Do. .. Tierra del Fuego Falkland Islands St^ Catharina .. Rio de Janeiro . Do annually. 177410 1828.. 8,0 1820 to 1834.. 8,2 1822 to 1827.. 8,4 1751 to 1817.. 4,8 1817 to 1832.. 4,3 2d. South dip decreasing. New Zealand .. .. 1824101835 .. 1,2 annually.^ 3f?. South dip increasing. 1775 to 1B36 .. 0,5 annually. Ml. South dip decreasing. annually. 171010 1799.. 0,4' 1799 to 1835.. 4,9 1794 to 1835 10,0 1710 to 1786.. 3,7 1786 to 1835.-8,3 In the 2d and 3d divisions the annual change is small ; in the 1st and 4th considerably greater. It is greatest at the southern station in South America ; the observations at Valparaiso,|fCon- cep9ion, Tierra del Fuegoj and the Falkland Islands, concur in shewing it to exceed 8'. The observations at Ascension, St. Helena, and the Cape of Good Hope, concur in shewing an annual change in that quarter of the 1st division exceeding 6'. As the south dip decreases in South America, and increases in Africa, it is obvious that somewhere intermediately the dip must be stationary. Between Africa and New Zealand, for the same reason, there must be a second locality so characterised- Between New Zealand and Otaheite, a third ; and between Otaheite and the west coast of South America, a fourth. Captain Fitz-Roy has * This is derived fronn the observations of Captains Duperrey and Fitz-Roy at the Bay of Islands, in Lat. 35°. 16'. The interval is short ; but the indication receives confirmation from the observations of Captains Cook and Vancouver at Dusky Bay, New Zealand, in Lat. 45°. 47'. Cook -. .. 1773 .. 70°. 06' > i<. 4 annual decrease. Vancouver.. 1791 .- 69. 43 >