behind the stem-post, and so support the vessel. He increased the stern wave, by making the vessel of such a form, that the dividing-lines should close with less taper, supposing that this wave would help the vessel onwards. But, as his mathematics are not always quite correct, it is hard to appreciate the result. And moreover, this object could be obtained by any curve at first parallel to the keel, and gradually leaving that direction; so that I do not quite comprehend why he should fix upon the curve of sines for the water-lines. But it seems that an inflected line must offer more resistance than a simple curve. He says, that the wave at the bow is of the form of a curve of sines; that is, the section by a vertical plane presents that curve. Assuming that this be true, why does he apply this curve to the horizontal plane of the water-line? There is no regular publication on the subject from his own pen (except in a periodical, in the year 1838); so that, very likely, he is not rightly understood, and an injustice has been done to him, in making him stand godfather to a principle which is not his own. Would it not, however, be better perhaps to apply a cycloidal arc to the dividing-lines of the bows (if such a principle as the above must be adopted), and have the dividing-lines aft much more tapered, and as nearly straight as possible; so that the particles at the stern may not fly off at a tangent, or, in other words, that there be caused as little suction as possible to the stern, and that the statical pressure at the stern should not be decreased. (The reason for mentioning the cycloidal arc as a substitute for the curve of sines in the bow, we shall presently investigate.) Mr. Griffiths adopts the wave theory, and attempts to explain it, while he laughs at the prin ciple upon which it is founded. He sneers at Mr. Russell's "ignorance" for not knowing that steamers have been built in America, which are so sharp as to have no wave. The wave may be so lengthened as not to be remarkable; but there must be some wave. However, he saves any one the trouble of contradicting him, for with a noble generosity, he takes the unpleasant duty upon his own shoulders: he finds it a curious thing that these vessels should run aground when passing swiftly over shallows, on which there is quite sufficient water to float them when at rest. Is not this the result of the wave at the bow and stern, and the hollow in the water amidships? Let any one watch the 'Clasper' eight oars, at Cambridge or Oxford. They are longer and narrower in proportion than any steamer; yet the two waves are quite discernible. To find the resultant of the increment of pressure, p, when the vessel is set in motion. We have seen that the vessel, when at rest, is pressed on all sides by the water; the pressure on a unit of surface varying as the depth, and acting in a direction normal to the surface. The resultant of these pressures is equal to the whole weight of the ship=D, and acts in a vertical direction through the centre of gravity of the ship. But when the vessel is set in motion, the particles of water would meet the vessel with a velocity v, suppose, and exert on a unit of surface (supposing it perpendicular to the direction of the vessel) some v force p: (where Р is not a moving force, as there t is no momentum to be considered). But, as we have said above, the water at the bows has a velocity with the vessel. Hence, at the bows p |