The air contained within the Upper : part of a diving-bell not only debars the ingress of water, but, like the ratified air in the balloon, gives the machine such a buoyancy, that, unless made very substan tial, and duly, laden at the bottom, or broadest part, it would sink with difficul ty, and be apt to turn on its side, so that the air would escape. Under the head of . Dtvitro-bell, the reader will find an ample . detail of the inventions hitherto extant in that branch of adventure. • With regard to the depth to which float ing bodies become immersed in fluids, we may consider the following general principles, or propositions, to be suffi cient for the purpose of our readers.— Bodies, whose bases, or bottoms, are an gular, like the keels of ships, will be immersed deeper than those whose bases are flat, such as barges : hence sharp built vessels necessarily (to use the tech nical term) "-draw more water" than those of a more obtpe form.: the reason of which is easily demonstrated, viz. As every body floating on a fluid wilthe im mersed in proportion to its weight, and will displace a quantity of water equal thereto, it follows, that as a triangle is equal to only half& parallelogram equal base and altitude, a parallelogram (or flat bottomed vessel) will, under equal pres sure, sink only half the depth of a triangu lar shaped bottom, of equal base and alti tude. For the same reason, vessels • that have sharp stems make an easier passage though the water than such as are more "bluff," or obtese, " at the bowst" the more acute the triangle in that part, the less the resistance ; for the triangle dis places only half the quantity of waterthat would be removed by a parallelogram of equal base and altitude ; ergo, it would proceed twice as far, within a given time, as the latter, were not the friction, in some degree, increased.
It must be obvious, that whether the vessel alone, or the circumstance of her being laden, cause her to weigh more than the quan ity of water displated by her whole bulk, up to the very gunwale, is not material; for in such case she cannot float, but must be depressed by the sum of spe cific gravity thus produced. This will appear in a very natural and simple man ner, if we load a cup with small shot, &c. for, though partly empty, the cup will sink whenever the whole weight may exceed that of the water displaced- Both the cup and the shot are, however, specifically heavier than their bulk of water, and the former would sink if let in sideways ; but then it would only displace a quantity of water corresponding with its own bulk, which would be trivial, when compared with that removed by its pressure as a floating body. On the other hand, we
find that a ship may be laden with cotton, which is far lighter than water, so as to sink, at least to a level with the water, though not to precipitate to the bottom, unless forced by the adjunction, in what ever form or manner, of such other sub stances as are heavier th m water,by which the levity of the cotton may not only be counterpoised, but exceeded. In India, where the principles of hydrostatics are absolutely unknown, the peasants make rafts of the straw, which they perceive to be lighter than water, and on them load the corn threshed from that straw, per ceiving it to be heavier than water. Thus they act upon the best principles, merely ' from observation ! Perhaps, among the most curious cir cumstances that come within the verge of our subject, nothing can more fully exem plify what has been advanced, than the fact, well known, of some vessels sailing better upon than before the wind. We have no doubt that, if the forms of their bottoms were correctly ascertained, they would be found to present such a surface in the former position, when " keeled a little," as created a more favourable po sitionof the gravity of the vessel, though it must be at least equal, or, indeed, great er, if much pressed by the wind, than in the latter position.
Before we quit this subject, it is neces sary to inform the reader, that, except in cases relating purely to statics, few in stances occur, in which the various mat ters appertaining to hydrostatics can be treated in a manner perfectly abstracted from pneumatics, or from hydrodynamics. Under the head of FLUIDS, and of HT. PRAUL1CS, we have treated of the princi ples of fluids in motion, in such a way as may give a popular idea of those very in tricate subjects ; recommending to the student to read the whole contained under those articles with attention, and combin ing their several actions as derived from one great principle.