374 
LIEUT. -GENERAL SABINE ON TERRESTRIAL MAGNETISM. 
propose to Her Majesty’s Government, in 1844, the employment of a third ship, supplied 
with instruments of a similar construction, in a portion of the high southern latitudes 
comprised between the meridians of 0° and 125° E., which was not comprehended in the 
voyages of the 4 Erebus ’ and ‘ Terror.’ The Admiralty having acceded to this proposi- 
tion, the ‘ Pagoda,’ a barque of 300 tons, was hired for the purpose by the Admiral Com- 
manding at the Cape of Good Hope, and, having been duly strengthened for ice-naviga- 
tion, was fitted for a voyage of some months’ duration. Two officers were employed 
conjointly in the direction of this portion of the Survey, Lieut, (since Hear- Admiral) 
J. E. L. Moore and Lieut, (since Colonel) Henry Clerk of the Royal Artillery. Lieut. 
Moore had been one of the officers of the 4 Terror ’ in Sir James Ross’s expedition, and 
was consequently accustomed to the navigation of the high latitudes, as well as practised 
in magnetic observations, having taken a very prominent share in those of the ‘ Terror.’ 
Lieut. Clerk had been attached by Lord Vivian, Master-General of the Ordnance, to 
the Magnetic Observatory at the Cape of Good Hope, with the express view of being- 
employed in a Magnetic Survey, either of the Colony itself, or of such part of the globe 
as might be conveniently accessible from it,- and, in the passage from England to the 
Cape, had had an opportunity of practising with the instruments employed in a mag- 
netic survey conducted on the ocean. The ‘ Pagoda ’ completed her survey between the 
60th and 70th parallels, and between the 4th and 96th meridians of East longitude, 
returning to the Cape by South Australia and Mauritius. The results were communi- 
cated to the Royal Society in the same provisional form with those of the 4 Erebus ’ and 
4 Terror ’ in the VIll.th Number of these Contributions, in which Number were also 
included the determinations of the Inclination and Intensity made at sea by Lieut. 
Alexander Smith, R.N., and by Lieut. Joseph Dayman, R.N. (officers employed at the 
Magnetic Observatory at ILobarton), on passages from Hobarton to the Cape of Good 
Hope, in which they were provided with instruments similar to those employed by Sir 
James Ross. 
One of the chief difficulties anticipated in these undertakings arose from the circum- 
stance that magnetic determinations made at sea are necessarily subject to the disturbing 
influence of the iron which cannot be wholly dispensed with in the equipment of a ship 
fitted for general navigation, and which, even when reduced to its smallest practicable 
amount, and kept as far as may be possible at a distance from the magnetic instruments, 
still exercises a disturbing influence which in the high latitudes becomes excessive, and 
requires to be met by appropriate corrections. The disturbing influence of the ship’s 
iron on the pointing of the compasses had attracted the notice of some of the most 
careful marine surveyors towards the close of the last century, and had been met by 
empirical rules of inconsiderable extent and partial application — when in 1818 the 
4 Isabella ’ and 4 Alexander,’ ships of a class corresponding in many respects to the 
4 Erebus ’ and 4 Terror,’ were employed in the first expedition to the Arctic Polar Regions, 
and were led by the objects of the expedition into localities where the navigation had 
to be conducted in magnetic Inclinations exceeding 85°, when the superior influence of 
