A variety of opinions have been entertained respecting the relative advantages of horizontal and vertical windmills. Mr. Smeaton gives a decided preference to the latter; but, as he asserts that horizontal windmills have only one-eighth or one-tenth of the power of vertical ones, he certainly forms too low an estimate of their power. Mr. Beutson, on the contrary, who has a patent for the construction of a new horizontal windmill, seems to be prejudiced in their favour. From an impartial investigation, it will probably appear, that the truth lies between these two opposite opinions; but before entering on this discussion, we must first consider the nature and form of horizontal windmills ; which we shall do in presenting the reader with a description of the horizontal mill erected at Margate by Captain Hooper.
Fig. 149 is an upright section, and fig. 150 a plan of the building. B II are the side walls of an octagonal building which contains the machinery. These walls are surmounted by a strong timber framing C G, of the same form as the building, and connected at top by cross-framing to support the roof, and also the upper pivot of the main vertical shaft A A, which has three sets of arms, B B, C C, D D, framed so it at that part which rises above the height of the walls. The arms are strengthened and supported by diagonal braces, and their extremities are bolted to octagonal -wood frames, round which the vanes or floats E E are fixed, as seen in outline in fig. 150, so as to form a large wheel, resembling a water-wheel, which is less than the size of the house by about 18 inches all round This space is occupied by a number of vertical boards or blinds F F, turning on pivots at top and bottom, and placed obliquely, so as to overlap each other, and completely shut out the wind, and stop the mill, by forming a close case surrounding the wheel; but they can be moved altogether upon their pivots to allow the wind to blow in the direction of a tangent upon the vanes on one side of the wheel, at the time the other side is completely shaded or defended by the boarding. The position of the blinds is clearly shown at F F, fig. 150.
At the lower end of the vertical shaft A A, a large spur-wheel a a is fixed, which gives motion to a pinion c, upon a small vertical axis d, whose upper pivot turns in a bearing bolted to an eirdei of the floor n. Above the pinion c, a spur- wheel e a placed, to give motion to two small pinions, on the upper ends of the spindles g, of the mill-stone h. Another pinion is situated at the opposite side of the great spur-wheel a a, to give motion to a third pair of Bull-stones, which are used when the wind is very strong; and then the wheel turns so quick as not to need the extra wheel e to give the requisite velocity to the stones. The weight of the main vertical shaft is borne by a strong timber b, having a brass box placed on it to receive the lower pivot of the shaft. It is supported at its ends by cross-beams mortised into the upright posts b J, as shown in the plan, fig. 150.
A floor or roof is thrown across the top of the brick-building to protect the machinery from the weather, and to prevent the rain blowing down the opening through which the shaft descends, a broad circular hoop K is fixed to the floor, and is surrounded by another hoop or cue L, which it fixed to the arms D D of the wheel. This last is of such a size, as exactly to go over the hoop K, without touching it when the wheel turns round. By this means, the rain is completely excluded from the upper room M, which serves as a granary, being fitted up with the bins m m, to contain the different sorts of grain which is raised up by the sack- tackle. A wheel i is fixed on the main shaft, having cogs projecting from both sides. Those at the under side work into a pinion on the end of the roller K, which is for the purpose of drawing up sacks. Another pinion is situated above the wheel i, which has a roller projecting out over the flap- doors seen at p, in fig. 150, to land the sacks upon. The two pinions m m, fig. 150, ure turned by the great wheel a a, and are for giving motion to the dressing and bolting machines, which are placed upon the floor N, but arc not shown in the drawing, being exactly similar to the dressing machines used in all flour-mills.
The cogs upon the great wheel a are not so broad as the rim itself, leaving a plain rim about three inches broad. This is encompassed by a broad iron hoop, which is made fast at one end to the upright post b in the other being jointed to a strong lever n, to the extreme end of which a purchase ? is attached, and the fall is made fast to iron pins on the top of a frame fixed to the ground. This apparatus answers the purpose of the brake or gripe used in common windmills to stop their motion. By pulling the fall of the purchase o, it causes the iron strap to embrace the great wheel, and produces a resistance sufficient to stop the wheel. The mill can be regulated in its motion, or stopped entirely, by opening or shutting the blinds F, which surround the fan-wheel. They are all moved at once by a circular ring of wood situated just beneath the lower end« of the blinds upon the floor 11, being connected with each blind by a short iron link. The ring is moved round by a rack and spindle which descend into the mill-room below, for the convenience of the miller.