How did douglas makes sure that he conquered the old terror?

Explanation: To make sure that he had conquered fear, Douglas went to Lake Wentworth in New Hampshire dived in and swam two miles across the lake to Stamp Act Island. Only once when he was in the middle of the lake, did the terror return. But he confronted it and swam on. He them swam across Warm Lake to the other shore and back. He was sure of having conquered his fear of water.