16 SEVENTH REPORT—-1837. 
a survey of the coast of South America from Rio de Janeiro to 
Valparaiso, carried on under the orders of the British Govern- 
ment by Capt. Philip Parker King of the Royal Navy. They 
were undertaken at the request of M. Hansteen, and with an 
apparatus for horizontal vibration with which Capt. King was 
furnished by him. A copy of the observations was transmitted 
from time to time, as they were made, to M. Hansteen, who em- 
ployed the results, computed provisionally, in his map of the 
intensity, published in the Annalen der Physik, vol. xxviii. 
The observations themselves have not yet been published, 
having been given by Capt. King to his successor in the survey, 
Capt. Fitz Roy, to be published when the latter should return 
to England. On his return, which took place late in 1836, 
Capt. Fitz Roy placed Capt. King’s magnetic observations in my 
hands (together with his own, of which a separate notice will be 
given in the sequel,) to calculate and arrange for publication 
in an account which he is now preparing for the press, of the ~ 
proceedings of Capt. King and himself during the survey. 
Meantime I have Capt. Fitz Roy’s permission to introduce Capt. 
King’s results into this memoir. 
The needle with which M. Hansteen supplied Capt. King sus- 
tained a very considerable loss of magnetism during the four 
years it was employed by that officer. Its time of vibration in- 
creased between March 22, 1826, and January 24, 1831, (on 
which days it was tried in the garden of the Royal Observatory 
at Greenwich,) from 734°5 seconds in 1826, to 775°8 seconds in 
1831. A change of such magnitude in the magnetic intensity 
of the instrument employed to measure the variations of the 
terrestrial intensity, and which ought itself, therefore, to be in- 
variable, would, in ordinary circumstances, have prevented any 
satisfactory conclusion whatsoever being drawn from the obser- 
vations. Fortunately, from the nature of the duties in which 
Capt. King was engaged, he had occasion to return frequently 
to the same anchorages; and as he was extremely careful to 
re-examine the needle on every such return, we have the means 
of knowing by direct observation the amount of the loss it 
sustained in certain portions of the time of its employment. 
There are eleven stations at which the force was observed 
on the east and west coasts of South America, and two in ports 
of the Atlantic on the outward voyage. By the practice re- 
ferred to, of repeating observations at the same station at di- 
stant intervals, the South American stations are so linked toge- 
ther and connected, that by adopting a method similar to that 
used in determining chronometrical differences of longitude, we 
may compute and assign the intensity at each, in reference to 
