LINES OF MAGNETIC DECLINATION IN THE ATLANTIC. 
175 
collected in Table VIIL, and are also exhibited in the Map in larger and more con- 
spicuous figures than those which represent the determinations from which they are 
severally derived. The map thus contains, first, the original determinations reduced 
to the mean epoch ; secondly, the elements, or mean values for the points of inter- 
section, derived from the determinations ; and thirdly, the lines themselves derived 
from the elements, so that the degree of accordance of the elements and of the lines 
with the sources from whence they are derived may be everywhere judged of by 
inspection. 
The determinations employed in this Memoir have been obtained from the following 
sources : — 
(A.) Sea observations uncorrected for the effects of the Ship's Iron. 
1. Observations made in the corvette Krotkoi by Dr. Adolph Erman in her home- 
ward voyage from Cape Horn to Portsmouth in 1830; extracted from Erman’s Reise 
urn die Erde. 
2. Observations made on board the Beagle, Captain Robert FitzRoy, on her out- 
ward passage from England to South America in 1831 and 1832, and whilst on the 
South American station, east of Cape Horn, in 1833 and 1834 ; and on her homeward 
passage in 1836 from the Cape of Good Hope to the British Channel; extracted from 
the published account of the voyage. 
3. Observations made on board the corvette La Bonite, Captain Vaillant, on her 
outward passage from Toulon round Cape Horn in 1836, and on her homeward 
passage in 1837 from the Cape of Good Hope to Brest ; extracted from the published 
account of the voyage. 
4. Observations made on board the frigate La Venus, Captain (since Admiral) Du 
Petit-Thouars, in her outward passage from France round Cape Horn in 1837, and 
in her homeward passage in 1839 from the Cape of Good Hope to Brest ; extracted 
from the published account of the voyage. 
5. Observations made by Captain (since Admiral) Berard, on board the brig Le 
Voltigeur in a voyage in 1838 from Toulon to Vera Cruz, and from thence by New 
York to Brest ; and on board the corvette Le Rhin, on her outward passage from 
Toulon to the Cape of Good Hope in 1842, and in her homeward passage from Cape 
Horn by St. Helena to Toulon in 1846 ; from a MS, obligingly communicated to me 
by Captain Duperrey, Membre de ITnstitut. 
6. Observations made on board La Prevoyante by Captain Jehenne, on a passage 
from the Cape of Good Hope by St. Helena to Cayenne in 1842 ; extracted from the 
Annales Maritimes et Coloniales for 1843. 
7. Observations made in H.M.S. Curagoa, Captain Sir Thomas Sabine Pasley, Bart,, 
whilst on the South American station in 1843 and 1844; MSS. 
2 A 2 
