Of course there was a valve in the upper hemisphere which would permit of a rapid descent if found necessary.
All these contrivances are well known, but they were here fitted in perfection.
The "Go-Ahead" then rose vertically.

Her enormous dimensions gradually grew smaller to the eye, and the necks of the crowd were almost cricked as they gazed into the air.

Gradually the whale became a porpoise, and the porpoise became a gudgeon.

The ascensional movement did not cease until the "Go-Ahead" had reached a height of fourteen thousand feet.

But the air was so free from mist that she remained clearly visible.
However, she remained over the clearing as if she were a fixture.