and in the rapid falls of rivers.  Of the mode of swimming of fishes of a round form.  How it is that animals which have not long hind quartres cannot swim.  How it is that all other animals which have feet with toes, know by nature how to swim, excepting man.  In what way man ought to learn to swim.  Of the way in which man may rest on the water.  How man may protect himself against whirlpools or eddies in the water, which drag him down.  How a man dragged to the bottom must seek the reflux which will throw him up from the depths.  How he ought to move his arms.  How to swim on his back.  How he can and how he cannot stay under water unless he can hold his breath [13].  How by means of a certain machine many people may stay some time under water.  How and why I do not describe my method of remaining under water, or how long I can stay without eating; and I do not publish nor divulge these by reason of the evil nature of men who would use them as means of destruction at the bottom of the sea, by sending ships to the bottom, and sinking them together with the men in them.  And although I will impart others, there is no danger in them; because the mouth of the tube, by which you breathe, is above the water supported on bags or corks [19].

[Footnote:  L. 13-19 will also be found in Vol.  I No. 1.]

On naval warfare (1115. 1116).

1115.

Supposing in a battle between ships and galleys that the ships are victorious by reason of the high of heir tops, you must haul the yard up almost to the top of the mast, and at the extremity of the yard, that is the end which is turned towards the enemy, have a small cage fastened, wrapped up below and all round in a great mattress full of cotton so that it may not be injured by the bombs; then, with the capstan, haul down the opposite end of this yard and the top on the opposite side will go up so high, that it will be far above the round-top of the ship, and you will easily drive out the men that are in it.  But it is necessary that the men who are in the galley should go to the opposite side of it so as to afford a counterpoise to the weight of the men placed inside the cage on the yard.

1116.

If you want to build an armada for the sea employ these ships to ram in the enemy’s ships.  That is, make ships 100 feet long and 8 feet wide, but arranged so that the left hand rowers may have their oars to the right side of the ship, and the right hand ones to the left side, as is shown at M, so that the leverage of the oars may be longer.  And the said ship may be one foot and a half thick, that is made with cross beams within and without, with planks in contrary directions.  And this ship must have attached to it, a foot below the water, an iron-shod spike of about the weight and size of an anvil; and this, by force of oars may, after it has given the first blow, be drawn back, and driven forward again with fury give a second blow, and then a third, and so many as to destroy the other ship.