should be nearly double its length; whereas, usually, the length is made almost 5 times the width! The following peculiar construction of the sails of a windmill, used in the vicinity of Lisbon, merits notice from its being, according to the opinion of Lord Somerville, superior to those used in Great Britain.-Their advantages are thus detailed by his Lordship: 1. The broad part of the sail is at the end of the lever, and thus an equal resistance may be overcome with less length of arms. 2. The sails, constructed upon this plan, may be set to draw in a manner similar to the staysails of a ship; and, as they are swelled more than those of common mills, they render it unnecessary to bring the mill so frequently to the wind: a practice attended with considerable trouble. The following sketch will, perhaps, convey a better idea of its utility, and, at the same time, of its applicability to nautical purposes. For the following calculation respecting elliptical sails, I am indebted to a friend. "If the sails of a windmill form a complete ellipsis, whose transverse diameter is 80 feet, and conjugate 64, and are so disposed that the conjugate, or rather semi-conjugate, forms the length of the arms, and by this disposition receives the whole force of the wind, and loses none, it is then to be observed that these sails embrace a surface, or rather present to the wind a surface of 4,021,248 square feet; then, admitting the wind to be brisk, or what nautical men term a snug breeze,' the wind, at that rate, acts with a force of about a pound on each square foot, or 4021 lbs. on the 6 sails combined; or supposing, for argument, the dimensions or surface of the sails equal, 670, 208 lbs. on each sail. Now, as the sails are a lever of the first order, of course the power of each sail is in proportion to the length of the lever, (or the circumference described by it,) compared with the semi-axis, (or its circumference); therefore allowing the circumference of the axis to be of the circumference of the circle described by the revolution of a sail, in that case each sail will have the power of 670, 208 x 3221,446, 656 lbs. and the whole ellipsis 6 times that, viz. 128, 679, 936 lbs. or capable of removing 574% tons, exclusive of friction." : Windmill sails may also be made to act horizontally. A scientific mill was, some time since, constructed at Battersea, on the principle, I conjecture, of the wind-towers of the Asiatics, only that a number of horizontal sails revolved around the same shaft.' Query; Might not those sails, or even those of the Portuguese windmill, be advantageously employed as auxiliary means (should such be found requisite to propel ships of the greatest dimensions) as the stud or stay-sails, &c. of ships are in light breezes ? and instead of being confined to three rectangular, or elliptical sails, might not the number be increased to embrace a surface nearly equal to the present sails of a ship when set? Independently of those means, or the improvement of the common rectangular sail, a considerable accession of force, I am convinced, mightbe obtained by an attention to the construction and more scientific application of the paddles themselves. The present form was adopted in the infancy of the invention of steam-boats; and, although numerous experiments have been tried, without, unfortunately, any practical good having resulted from them; it is yet evident that much remains to be done. From the circumstance of half the wheel only being submerged, at any one time during its action, it follows that the wind must oppose a very considerable resistance to its rotatory motion; the effect of which may be more easily conceived when it is known that it performs, upon an average, 40 revolutions per minute. Hence an incalculable advantage would be obtained could the paddles be brought to present a smaller surface to the retarding force of the air, similar to the oars of a boat, which are said to be feathered when their edges alone are opposed to the wind during the interval of the strokes. As my present proposition is to apply another power to the machinery in use, I will trust to experience more matured, to suggest a remedy for this defect in the mechanical propulsion of vessels by steam or otherwise. A few of the advantages which this plan, if adopted, would possess over steam, have been already detailed; that it would possess as great a superiority over the present mode of navigation, must be equally evident; for, whilst it would share with steam the singular advantage of sailing against wind or tide, whereby navigation may be rendered comparatively safe, the simplicity of the method proposed would render it infinitely preferable to both. Masts, sails, ropes, spars, &c. form no inconsiderable share of the sum total of a vessel's cost, and, to a maritime nation, they become of national importance, when derived from foreign sources. What the author now submits to the public is, at best, but à hasty sketch. He has merely embodied those ideas which rapidly 1 See Dr. Gregory's Dictionary of Arts and Sciences. Art. Windmill. occurred to him on a first view of the subject; and, as his only object is to court an investigation of a plan which, if successful, must tend, in so great a degree, towards the advancement of the interests and happiness of mankind, he sincerely trusts that it will not be deemed altogether undeserving of experiment. The author would feel indebted for any communication on the subject of the foregoing "suggestion," addressed to him through the publisher. |