Finely balanced as they were, they still communicated some slight vibration to the ship.

The Master snicked the switch of the magnetic-anchor release; and now the last bond that held _Nissr_ to her cradle was broken.

As soon as the air-skid currents should be set going, she would be ready for her flight.
This moment was not long in coming.

Another turn of a switch, and all at once, far below, a faint, continuous hissing made itself audible.
Compressed air, forced through thousands of holes at the bottom of the floats, was interposing a gaseous cushion between those floats and the track, just as it could do between them and the earth wherever _Nissr_ should alight.
Suspended thus on a thin layer of air, perhaps no more than a sixteenth of an inch thick but infinitely less friction-producing than the finest ball-bearing wheels and quite incapable of being broken, the ship now waited only the application of the power in her vast propellers.
"Let in numbers two and four," commanded the Master, suddenly, into the engine-room telephone.

"In five seconds after we start, hook up one and three; and five later, the other two." "Aye, aye, sir," came back the voice of Auchincloss, chief engineer.
"Ready, sir!" Almost at once, the vibration of the engines altered, grew more marked, seemed to be taking hold of something with strong but easy effort.