1 But let that man with better sense advise

advise > consider

2 That of the world least part to us is read:

least > [the least] read > discerned; known

3 And daily how through hardy enterprise 4 Many great regions are discovered, 5 Which to late age were never mentioned.

to late age > [to those living in recent times]

6 Who ever heard of the Indian Peru?

Indian > (America was thought to be India)

7 Or who in venturous vessel measured

venturous > bold, daring; adventurous measured > measured; traversed