Why did James Clark Ross go to Antarctica?

In 1839-43, British naval officer and Arctic explorer James Clark Ross led an expedition to the seas adjacent to Antarctica. Ross's three ship expedition sailed on HMS Erebus and Terror. His goals, according to one historian, were:

1. To complete the discovery of land known to exist south of South Americca;

2. If no mainland or large island presented itself at that point to extend his voyage by penetrating to a high southern parallel with a view to examine the phenomena of terrestial magnetism;

3. In any case to resolve "once the uncertainty which hangs over the discovery of lands reported east of Cape Horn;

4. And lastly if not inconsistent with any higher duty to take advantage of opportunities of advancing the interests of scientific knowledge generally."