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angle of C 4 = 14 will make four revolutions in the same time that it performs two revolutions with the sails at an angle of 263°, or one revolution with them at an angle of 45°. And if the angle be greater than 45°, as C1 = 564°, the rotation of the wheel upon its axis will be slower than the advance in a lateral direction; that is to say, it will make but one revolution while advancing one and a half times the distance of its own circumference. It will be evident, however, that if the angle of the wheel be at C 4 equal to 14°, the

quantity of water which must pass through it to cause one revolution of the wheel will be equal to the contents of a cylinder of the wheel's diameter and the depth E D; and that if the angle of the vane bear the direction C 3, then double the quantity of water will be required to produce one revolution. Again, if the wheel were to have double the number of floats, (which it ought to have, in order that the water may act upon the whole area of the cylinder or wheel,) then it may be inferred that double the power will be

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A convenient method of ascertaining the proper angles to be given to vanes or floats, at any required distance from the centre, when the angle at any one distance has been given, is shown by the diagram, fig. 8.

"The line B C represents the centre line of the wheel; D E, the circumference; a, b, c, d, e, and f, radial lines, drawn at distances, in respect to each other, corresponding with the angles to the centre of 14° 2′, 26° 14', 45°, 56° 19′, and 63° 26', as represented by the oblique lines Cb, Cc, Cd, Ce, Cf; g, h, i, k, l, m, n, o, p, q, r, s, t, u, other oblique lines, representing the various angles to the centre marked thereon; and 1, 2, 3, 4, 5, vertical lines parallel with the centre line, intersecting at equal distances the different radial and oblique lines. Now, the angle which any vane, with a given terminal angle, should have, at any point nearer to the centre, as 5, 4, 3, 2, or 1, will be the same as that of the oblique line, which is intersected at that point by one or other of the vertical lines, 5, 4, 3, 2, or 1. For example: a vane whose extremity is at an angle of 45°, if constructed according to the diagram, fig. 8, will present, at the distances from the centre of the wheel stated below, the angles set opposite thereto :

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may be thus demonstrated: by reference to the figure, it will be seen that the oblique line C d, which represents the angle of 45°, intersects the two radius lines above it, c and b, representing the base lines of angles of 26° 34' and 14° 2′, respectively, the one at the middle of its length, and the other at one-fourth of its length, from the centre. Hence it follows, that a vane or float, having an angular extremity of 45°, if it present one-half of the diameter of one of 26° 34', or one-fourth of the diameter of one of 14° 2′, will traverse the same distance in one revolution as either of the others. And what is true of any one angle will be equally true of all others; so that the following rule may be laid down, as of universal application.

"Rule. To find the angle of a float or vane at any required distance on the radius, the angle at some other distance being given.

"From the point C, on the radius line Ca, set off the angle of the given distance, and draw a line parallel to C B, from the given distance on the radius line Ca; then draw through the angle of the given distance another oblique line, until it intersects the parallel line to C B, and from the point of intersection draw a perpendicular to the line C B, on which set off the required distance; the distance C to B intersected by the lastfound line, divided by the length of the required distance, will give the tangent of the angle required, and from that tangent the angle required may be found by reference to any table of natural sines. For example: take the intersection of the horizontal line 9 and the vertical line 3; then, 9 ÷ 3 = 3, which is (nearly) the tangent of the angle 71° 34'."

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submerged in it, and moved forward in the direction of its axis; the wheel will then revolve freely, but without causing any material agitation either in the water or among the particles floating in it, both of which will remain stationary, those particles of floating matter only being acted upon which come in contact with the edges of the floats during rotation; showing clearly, that the water produces the rotating action with the least possible disturbance to itself. But let the same experiment be made with a model wheel constructed according to any of the common plans, with floats having plain surfaces, and set in any other position to the line of motion than have prescribed, there will then be more or less a surging of the water in front of the wheel, and the floating particles will be more or less agitated and tossed about, showing no less clearly, that the different form and position of the floats has caused an unnecessary obstruction to the passage of the water."

Wheels with vanes or floats set at angles found or determined by the preceding rules may be also applied to registering the velocity of bodies propelled through water, or of the wind. The manner of such application Mr. Biram illustrates by a description of the means to be adopted in the case of registering the velocity of a vessel at sea; but the details of this we shall for the present pass over.

In machines which act upon water or air, instead of the water or air acting upon them, and which derive their motion from some other source, as steam or animal power, a different principle from that which has been previously explained prevails. Mr. Biram examines, first, the case of propellers of vessels applied at the stern, and rotating in a plane perpendicular to the vessel's path.

"Here the useful effect produced by one revolution of the wheel may be said to be increased, the more the angles of the vanes or floats with the plane of motion is increased, within certain limits, which may also be illustrated by reference to figs. 6 and 7, before described; for if the vanes of the wheel, W, are at an angle of 563°, a cylinder of air or water will pass through it in one revolution, equal to the depth of the column HD; whereas, at 45° only, the depth of the said column would be only equal to G D, or the height of the wheel's circumference.'

Mr. Biram gives a representation of a pair of stern propellers constructed according to these conditions, and intended to be worked entirely under water. The

floats present at their extremities an angle of about 56°, (those of the two wheels being inclined reverse-wise to each other,) and are confined to their pheries. Each propeller or wheel is oneposition by two rings upon their perifourth less in diameter than the ordinary paddle-wheel, and only of one-fourth the width. "The result of several experiments made with these stern propellers," says Mr. Biram, "shows that they are, as nearly as may be, of equal power with the common paddle-wheel of larger dimensions, besides possessing the advantage of being worked under water, and at a part of the vessel where they do not interfere, as at the sides, with her sailing capabilities." The tremulous motion so often complained of in steam-vessels is also altogether obviated, or nearly so, in consequence of the oblique manner at which the paddles enter the water, and their reduced number.

In figs. 1 and 2, (see front page,) are given side and end views of a paddlewheel to be applied to the sides of vessels, constructed according to the conditions before explained.

"A A are two metal frames, having six arms and two concentric rings, which are fastened upon the axles on each side. The arms are fixed in an oblique position with regard to each other, those on the reverse side of the wheel being represented by a a. B B are six side-plates, which inclose the wheel on each side between the concentric rings of the frame, to the extent shown by the shaded parts, and are screwed or riveted to the frames A A. The shaded parts representing the said plates, together with the projecting ends of the paddles marked C, also show the outline of the paddles when viewed sideways, as in fig. 1. The paddles or floats, C C, which are also screwed or riveted to the frames A A, are placed diagonally across the shaded part of the wheel, and their extremities present an angle of 45° with the side of the wheel, and each point of the extremity radiating to the centre of the wheel, in lines parallel with the side, so that the angle which the paddle makes with the side of the wheel is constantly increasing from the extremity inwards, and would be at the inner ring about 68°. The better to illustrate the form of the wheels, I have given in figs. 3 and 3o diagrams of the side and end views of one of these paddles. In fig. 3, (in which the obliquity of the paddle is shown the reverse way to that intended to be represented by figs. 1 and 2,) B repre-D ing with C D, fig. 3.” sents the angle at the inner ring, correspond

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The form which Mr. Biram recommends for the ventilation of mines is the same as that before described as suitable for stern propellers. The sort of power best adapted to give them the required velocity will, of course, depend on local circumstances; but the following suggestions are thrown out, as generally worth attending to.

"When applied at the bottom of a shaft, down which there may happen to be a considerable fall of water, I would recommend that the water should be collected in a pipe, and made to impinge on inclined vanes at the extremity of the wheel, (which will give it a great velocity,) but the water vanes must be curved in the opposite direction to the vanes of the ventilator, and at the top

B

side they should be so inclosed as to prevent the air being forced through them, which would have a counteracting effect. When the ventilator is to be fixed at the top of a shaft, it will be found of advantage to have a revolving cap with sails over the pit mouth, on the same principle, exactly, as the selfregulating revolving caps of windmills, and on the sides of this cap, opposite to the wind, to have a circular opening, in which the ventilator may be placed. Such an apparatus would always act well when there was wind; and when the weather was calm, the ventilator might be set in motion by connecting it with a heavy weight, allowed to descend the shaft, and raised from the bottom of it, from time to time, by means of horse, or some other power."

THE BOCCIUS LIGHT.

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If

flickering is but concealed from view, and not really absent. Neither did Messrs. Brande and Parkes notice it in their Report, even though done to order -we presume, for the same reason. our correspondent will take a metal cylinder, of a line or two less than the exact diameter of the flame of a tallow candle, and pass it down just over the top of the flame, he will find that there is quite as little flickering visible as in the case of the Charing-cross phenomenon. Now, this is literally all that Mr. Boccius has done―all, indeed, that there is new in his most ridiculously-extolled invention.-ED. M. M.]

DESCRIPTIVE NOTICE OF THE GREAT NORTHERN" STEAMER (WITH SCREW
PROPELLER) -
-AND REPORT OF EXPERIMENTS MADE TO TEST THE DIAGONAL
SYSTEM OF PLANKING ON WHICH SHE IS CONSTRUCTED. BY GEORGE BAYLEY,
ESQ., MARINE SURVEYOR, LLOYD'S.
Sir,-The steam ship, the Great Nor-
thern, was launched at Londonderry, Sa-
turday the 30th July last, from the ship-

yard of Messrs. W. Coppin and Co. She is intended to be propelled by Smith's screw propeller, which is fitted in a space

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