do) at the average rate of 6 or 7 miles per hour, against wind and tide. If, therefore, one set impart a momentum equal to the propulsion of a vessel of moderate burden, three sets, placed longitudinally, as the masts of a ship, and acting independently of each other, with corresponding water-wheels, must impart momenta equal to a steam engine of 60 horse power, or the propulsion of a ship of very considerable dimensions. This is but a common inference deduced from known and acknowledged data, and which will, I conceive, render the proposition self-evident. But, supposing the means proposed to be inadequate to the end, an excess of power may be obtained, as I will presently show, by the scientific application of those means, which would greatly exceed any sum of force which might be required. The extremely rude construction of the windmill sails in common use, has often attracted the attention of men of science; and the only way to account for that species of mechanical power remaining unimproved for centuries, is, that a quantum of force was probably thereby acquired sufficient for the purposes for which it was employed.'' That this power might be increased, I will cite the following, out of numerous authorities, to prove; at the same time, I beg it to be understood, that it is far from my intention (although the subject may almost demand it) to swell this paper into an essay on windmill sails. Ferguson very ingeniously suggests, that, as the end of the sail nearest the axis cannot move with the same velocity which the tips, or farther ends, have, although the wind acts equally strong,-a better position, perhaps, than that of stretching them along the arms directly from the centre of motion, might be, to have them set perpendicularly across the farther ends of the arms, and there adjusted, lengthwise, to the proper angle; for, in that case, both ends of the sails would move with the same velocity, and, being farther from the centre of motion, they would have so much the more power. M. Parent, however, considers that the figure of the sails of a windmill should be elliptical, to receive the greatest impulse from the wind; and a windmill with 6 elliptical sails, he shows, would have more power than one with 4 only, as the force of the 6 would be greater than that of the 4 in the ratio of 245 to 231. 2 The same author also considers which form among the rectangular sails will be most advantageous, i. e., that which shall have the product of the surface by the lever of the wind, the greatest. The result of this inquiry is, that the width of the rectangular sail According to Ferguson this is the case; for he shows that, if the stones of mill revolve more than 70 times per minute, they pulverise the bran with the flower. Lect. on Mech. p. 52. 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 a hasty sketch. He has merely embodied those ideas which rapidly ? 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. |