It was so strong, and he felt himself so irresistibly overpowered and impelled towards a merely idle reverie, that, in order to think more clearly and shut out some strange and unreasoning enthrallment of his senses, he rose and sharply closed the window.

Then he sat down and reflected.
What was he doing here?
and what was the meaning of all this?
He had come simply to fulfill a duty to his past, and please a helpless and misunderstood old acquaintance.

He had performed that duty.

But he had incidentally learned a certain fact that might be important to this friend, and clearly his duty was simply to go back and report it.

He would gain nothing more in the way of corroboration of it by staying now, if further corroboration were required.