Bilge keels were first employed in warships for the purpose of obtaining a steadier gun platform, where the displacement was constant and the centre of gravity more or less a fixed and known point, generally not far from the waterline. The middle line at the waterline was assumed to be the axis of rotation. For the want of a better rule, due to the valving conditions of loading and centre gravity, with no definite data to go "upon, the same rule has been followed for merchant ships, the plane of the bilge diagonal being generally adopted as the most practical, even if not theoretically, the best position.
Froude proposed a formula for the rate of extinction of the angle of roll A O'B O, where "A" and "B" are constants depending on certain characteristic of the hull, but as these will alter for the same ship according to her loading, it is of little practical use for ordinary cargo carriers.
The sharpe bilge has a considerable effect on checking rolling due to the motion set up in the water by the more or'less rectangular form, and the consequent change in the form of the displacement. greater the round of bilge the greater the necessity for larger and more effective bilge keels.
From Hankow. July 20. Mr. and Mrs. E. J. Bannan, Miss N. R. De Jong, Mr. D. G, Gunnell.
Text read from the printed page and cleaned; old type leaves the occasional error.