The eye detects no joint in her skin plating save the sweeping hair-crack of the bow-rudder--Magniac's rudder that assured us the dominion of the unstable air and left its inventor penniless and half-blind. It is calculated to Castelli's "gull-wing" curve. Raise a few feet of that all but invisible plate three-eighths of an inch and she will yaw five miles to port or starboard ere she is under control again. Give her full helm and she returns on her track like a whip-lash. Cant the whole forward--a touch on the wheel will suffice--and she sweeps at your good direction up or down. Open the complete circle and she presents to the air a mushroom-head that will bring her up all standing within a half mile. "Yes," says Captain Hodgson, answering my thought, "Castelli thought he'd discovered the secret of controlling aeroplanes when he'd only found out how to steer dirigible balloons. Magniac invented his rudder to help war-boats ram each other; and war went out of fashion and Magniac he went out of his mind because he said he couldn't serve his country any more. I wonder if any of us ever know what we're really doing." "If you want to see the coach locked you'd better go aboard. It's due now," says Mr. Geary. I enter through the door amidships. There is nothing here for display. The inner skin of the gas-tanks comes down to within a foot or two of my head and turns over just short of the turn of the bilges. Liners and yachts disguise their tanks with decoration, but the G. P. O. serves them raw under a lick of gray official paint. The inner skin shuts off fifty feet of the bow and as much of the stern, but the bow-bulkhead is recessed for the lift-shunting apparatus as the stern is pierced for the shaft-tunnels. The engine-room lies almost amidships. Forward of it, extending to the turn of the bow tanks, is an aperture--a bottomless hatch at present--into which our coach will be locked. One looks down over the coamings three hundred feet to the despatching-caisson whence voices boom upward. The light below is obscured to a sound of thunder, as our coach rises on its guides. It enlarges rapidly from a postage-stamp to a playing-card; to a punt and last a pontoon. The two clerks, its crew, do not even look up as it comes into place. The Quebec letters fly under their fingers and leap into the docketed racks, while both captains and Mr. Geary satisfy themselves that the coach is locked home. A clerk passes the waybill over the hatch-coaming. Captain Purnall thumb-marks and passes it to Mr. Geary. Receipt has been given and taken. "Pleasant run," says Mr. Geary, and disappears through the door which a foot-high pneumatic compressor locks after him. "A-ah!" sighs the compressor released. Our holding-down clips part with a tang. We are clear.