I have watched for hours together in early life, in my walks across the bridge from Boston to Charlestown, the motions of the sea-gulls....

Often have I attempted to unravel the mystery of their motion so as to bring the principle of it to bear upon this very subject, but I never experimented upon it.

Many ingenious men, however, have experimented on air navigation, and have so far succeeded as to travel in the air many miles, but always with the current of wind in their favor.

By _navigating_ the atmosphere is meant something more than dropping down with the tide in a boat, without sails, or oars or other means of propulsion....

Birds not only rise in the air, but they can also propel themselves against the ordinary currents.