In an affidavit made in March, 1845, he states that in 1833 his attention was particularly called to the subject of oblique propulsion, and that under his direction propellers of various patterns and embodying these principles were fitted on a canal-boat named the "Francis," and later in 1834 to another called the "Annatorius."

From 1833 to 1839, or during the second half of this term of residence in London, he became in increasing measure absorbed in his work connected with the screw-propeller as a means of marine propulsion.

The question of who invented the screw-propeller in the absolute sense is entirely futile and without answer.

Likewise in 1823 Captain Delisle, of the French Engineers, presented a memorial to his Government in which he urged the use of the submerged propeller for the propulsion of steam vessels.

To quote from a letter to his friend, Mr. John O. Sargent, he says: "I visited this country at Mr. Ogden's most earnest solicitations to introduce my propeller on the canals and inland waters of the United States.

He noticed in the paper a propeller with a diameter of 15 ft. 6 in.

Then this memorial was remembered, and its author brought forward to receive his share of credit in connection with the adaptation of the propeller to marine propulsion.

To mitigate the shock of the air pump valves in cases in which a high speed has been desirable, as in the case of marine engines employed to drive the screw propeller without intermediate gearing, India rubber discs, resting on a perforated metal plate, are now generally adopted; but the India rubber should be very thick, and the guards employed to keep the discs down should be of the same diameter as the discs themselves.

These propellers, in fact, had a form far more nearly approaching the modern screw-propeller than did those which came somewhat later, and which marked the real entry of the screw-propeller into actual and practical service.

When it is required to disengage the propeller from the engine, the pins passing through the opposite eyes shown fig.

Q.Do you consider that the screw propeller is best adapted for vessels of full power, or for vessels with auxiliary power? A.It is, in my opinion, best adapted for vessels with auxiliary power, and it is a worse propeller than paddle wheels for vessels which have habitually to encounter strong head winds.

V. to VIII., 6 cwt.; and of this fuel a small fraction (about one-sixth) is consumed by the occasional working of the screw propellers at sharp bends.