Whom does Ulysses address in the second half of Lord Tennyson's poem? In the concluding lines of the poem, what qualities does he emphasize?

Towards the
middle of the poem,speaks of his son, Telemachus, in a manner that suggests he is pondering the
end of his rule and the shift of those responsibilities to Telemachus. He remarks on how
Telemachus has a good character and implies that he will be a good king, but seems to visualize
a rift or distance between them; "he works his works, I mine." It's almost as though
Ulysses is already half-departed.

His attention then turns to "[his]
mariners" - if we are to interpret this literally, he means the men who have sailed with
him before, probably the same ones that accompanied him on his earlier journeys as chronicled in
the Odyssey. Metaphorically, he might also be speaking to those who share
his sentiments, and long for exploration, and to "seek a newer world." In this sense,
if he is addressing any who share his feelings, including the reader, then he is speaking not to
specific characters but to an unseen third party in the sense of arather than a direct
conversation. 

The final lines of the poem, 

One equal temper of heroic hearts, 

Made weak by time and
fate, but strong in will 

To strive, to seek, to find, and not to
yield.

imply that he values strength of character
rather than of body; he knows that he and those like him are old, and not as strong as they once
were, but they retain a number of other virtues, such as their will. He exalts the ability of
the willful person to impose that will upon both nature and their own bodies, and resist the
slow and quiet decay that preys upon the old and inactive.