Narrative of the surveying voyages of His Majesty's ships Adventure and Beagle - LightNovelsOnl.com
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_1st. South dip increasing._
annually.
St. Helena 1754 to 1775 6,9'
Do. 1775 to 1836 6,5 Cape of Good Hope 1751 to 1775 7,2 Do. 1775 to 1836 6,6 Mauritius 1754 to 1824 1,3 Do. 1824 to 1836 0,8
To this division also belongs Ascension; but as the north end of the needle dips at that island, the change is _north dip diminis.h.i.+ng,_ instead of _south dip increasing._
Ascension 1754 to 1775 6,3 annually.
Do. 1775 to 1836 7,2 --
_2d. South dip decreasing._
New Zealand 1824 to 1835 1,2 annually.[211]
_3d. South dip increasing._
Otaheite 1775 to 1836 0,5 annually.
_4th. South dip decreasing._
annually.
Lima and Callao 1710 to 1799 0,4'
Do 1799 to 1835 4,9 Valparaiso 1794 to 1835 10,0 Concepcion 1710 to 1786 3,7 Do. 1786 to 1835 8,3 Tierra del Fuego 1774 to 1828 8,0 Falkland Islands 1820 to 1834 8,2 St^a Catharina 1822 to 1827 8,4 Rio de Janeiro 1751 to 1817 4,8 Do. 1817 to 1832 4,3
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, Concepcion, Tierra del Fuego, 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 {528} stations in the second of these localities only, between Africa and New Zealand. At Hobart Town, Sydney, and King George Sound, there appears to have been little or no change in the dip since the commencement of the present century.
The arrangement of the changes of dip in the southern hemisphere in four divisions, characterised by an alternate increase and decrease of dip, is in correspondence with the _double flexure_ of the lines of dip; and is a consequence of the western motion of the two southern magnetic poles.
Careful observations made at St. Petersburgh, have shewn that the annual change of the dip in the northern hemisphere takes place altogether between the months of May and December; there being in fact a small movement in an opposite direction between December and May. This fact is of great interest in its bearing on the study of the causes of the magnetic phenomena. We have as yet no corresponding knowledge in regard to the southern hemisphere. The magnitude of the annual change which Captain Fitz-Roy's observations show is now taking place at the Cape of Good Hope, is deserving of attention in this respect. A large amount of annual change is obviously highly favourable for a determination of all the circ.u.mstances belonging to it; and its existence at the Cape, where there is already a fixed observatory, points to that station as most eligible for this investigation.
The observations at Ascension shew that the epoch is fast approaching when the needle will pa.s.s from north to south dip at that island: it is extremely desirable that the period at which this change takes place should be determined with as much precision as possible.
III. _Intensity._
I have discussed in the Seventh Report of the British a.s.sociation, the very important inferences in regard to the general distribution of magnetism in the southern hemisphere, afforded by Captains King and Fitz-Roy's most valuable series of intensity observations; but no inferences in regard to the _changes_ which this phenomenon may be supposed to undergo can be drawn, as has been done in the cases of the variation and dip, because we possess no observations of the intensity made at a sufficiently early period to afford good materials for such a comparison.
EDWARD SABINE.
{529}
CATALOGUE OF THE MORE INTERESTING SPECIMENS OF NATURAL HISTORY THAT WERE COLLECTED DURING THE VOYAGE.
MAMMALIA.
1. MUSTELA ZORILLA. Desm:[212]
The skunk. This animal was found abundantly on the coast of Patagonia, between Monte Video and Cape Gregory, at the eastern entrance of the Strait of Magalhaens. It appeared to be the same species throughout the whole extent of the coast.--Mus. Zool. Soc.
2. MUSTELA LUTRIS.--Lin.
_Lutra marina_, Steller. Erxleb. Harlan; _Enhydra marina_, Fleming.
The sea otter exists, but not very plentifully, on the coast of Tierra del Fuego; we saw very few. The Fuegian Indians hunt them with dogs which are trained for the purpose.--Museum Zool. Soc.
3. CANIS.
The dogs belonging to the Fuegian Indians are certainly of the domesticated kind, originally obtained, probably, from the Spanish settlements at Buenos Ayres; generally they resemble the Esquimaux breed, but are much more diminutive in size.
4. CANIS VULPES.
Two if not three distinct species of the fox were brought home; one, of a small size, was thought to be a novelty; the other, perhaps, was only remarkable for its large size. Mr. Vigors thought the small one was quite new; the last is perhaps _C. cinereo argenteus_.--Museum of Zool. Soc.
5. FELIS PUMA.
Several were seen: a skeleton was found on the sh.o.r.es of the Strait, supposed to be one of the above species.
{530}
6. FELIS PAJEROS.--Desm. E. M. p. 231.
Chat pampa, D'Azara, 1. 179.
A variety of this species was given to me, by the Patagonian Indians, that had been recently killed; the skin was preserved, and is now in the museum of the Zoological Society. The following is the description of my specimen:--
The prevailing colour is a yellowish grey, deeper above, and gradually blending into the colour of the belly, chin, neck, inner part of the legs, the region of the a.n.u.s, and below the root of the tail, which are white; the under part of the neck and belly also are spotted with black, disposed in transverse bands; the fore arms have three similar transverse bands, and the thighs four encircling the legs; ears white inside and tipped black; eyes dark blue, eyelids whitish, corner of the eyes black, particularly at the anterior or inner angle; claws whitish, and paws black; whiskers white, and some long white hairs over the eyes; the canine teeth are very acute, and have the longitudinal grooves or angles deeply marked.
Inches.
Length of the body from the extremity of the nose to the root of the tail 29 Length of tail 11 Ditto head 6 Breadth of head between the ears 2-7/8 Height at the shoulder 12
7. OTARIA JUBATA.--Desm. E. M. No. 380.
The sea lion of Anson and other voyagers; numerous in the eastern entrance of the Strait, and particularly at Port San Julian and the neighbourhood of Port Desire.
8. OTARIA FLAVESCENS.--Desm: E. M. 250.
A young male was found on the beach, near Port Famine, that had been recently wounded by the Indians, and had crawled on sh.o.r.e to die.
9. CTENOMYS MAGELLANICUS. n. s.--Bennet.
This little animal possesses fur as soft as the chinchilla. It abounds in the neighbourhood of Cape Gregory, at the eastern entrance of the Strait of Magalhaens, and burrows under the {531} ground, which is so much undermined by them that it gives way at almost every step. It is a timid little fellow, feeds upon gra.s.s, and is eaten by the Patagonian Indians.--See Bennet in the Proceedings of the Zool. Soc. Dec. 22, 1835. A specimen is preserved in the Museum.
