pieces are thus adjusted. The width of each tion of the straight arm be uniform throughjet pipe being, as before mentioned, one out its length, and this area be six times fourth of the length of the chord subtending larger than that of the jet-pipe. A straight the circular arcs which determine the width

arm having its cross sectional area six times of the arm, if one-eighth of this chord be set larger than its jet-pipe will, in one revolu. off on each side of the circle 1, 4, 9, and a tion, expend about as much water as will fill portion of a circle having w for its centre, the arm, the motion of the water through be drawn from the outer end of the arm the arm being six times slower than its speed through each point so set off, and towards through the jet-pipe, and the radius of a 12, it will coincide with the outer and inner circle being to its circumference nearly as sides of the jet pipe. In practice, the corners one to six, the length of the arm being to 13 and 14 (fig. 3) should be rounded off in the circumference described by its jet-pipe the manner shown in fig. 2.

in the same proportion. But the capacity " In cases where the machine moves so of the curved arm being the same as that of fast as not to allow time for the water leaving the straight arm, as much water as will fill it to fall a distance equal to the depth of the the former will be the quantity required arm, before the next arm comes up, the during one revolution of the machine. From water which leaves the one arm will be this it is clear, that the water which is lear. struck by the other, and thus the machine

ing the centre, w, at any instant when the will be in some measure retarded. When arm is in the position shown in fig. 3, will, the machine moves at a speed slower than after the arm has made one revolution, be that of the water, this defect may, in most out at 1, the beginning of the jet-pipe. The cases, be remedied by simply turning the cross sectional areas of the arm are so adaptouter extremity of the jet pipes a little out ed to the curvature of the line 1 dl rio, wards, in order that the water which leaves that whenever any point, as p, in the arm, the one arm may be thrown outside the arrives at the point o, in the radius w 1, the other. The width of the jet pipes in relation water which left the centre when the arm to that of the arms will be regulated by the was in the position shown in the figure, will velocity of the machine in relation to that also have arrived at or near the point o, and of the water which works it. Thus, if the thus the water will flow from the centre of machine mc: '3 at the same speed as the the machine out to the jet-piece in a straight water, the width of the outer end of each jet line, or nearly so, when the machine is in piece should be about one-third of the motion." length of the chord subtending the arcs,

When a jet-pipe moves at a speed which determine the breadth of the arm.

slower than that of the water issuing The machine which we have just described should move at a speed about one-third

from it, the arm may have a greater caslower than that of the water, and if the

pacity than it would have if the motion machine moves at about three-fourths of the

of the jet-pipe were as great as that of the speed of the water, the chord which sub water without carrying the water round tends the arcs which determine the breadth with it; for when the speed of the arm of the arm should be two and a half times is reduced, the speed of the water flowing longer than the width of the jet pipe." through it may also be diminished. The

kind of arm shown in figs. 1, 2, and 3 The advantage of the present machine over that first invented by Mr. Whitelaw

has an uniform depth throughout its consists in its preventing more effectually

length, and its cross section at any point

is of a rectangular form; but it will be the water from being carried round with the arms. Of this the patentees give the

evident that each cross section of an arm following very clear and satisfactory ex

and jet-pipe may be of a square, circular, planation:

or any other suitable form, provided the

square, circular, or other form of arm “ Suppose, for the sake of illustration, has its cross sectional areas at the correthat the centre of the jet-pipes move at a sponding distances from the centre u, speed as great as that of the water issuing

the same as the cross sectional areas of from them. In this case, the width of each

the kind of arm shown in figs. 1, 2, jet-pipe will be about one-sixth of the width

and 3. of the arm, its width being marked off on circular arcs, in the manner before men

For working in tail water, the patentees tioned. An arm of the kind represented in

recommend such a modification of the fig. 3, if its dimensions be as last given,

machine, figs. 1 and 2, as is represented will contain about as much water as will fill in figs. 4 and 5. Here two circular plates a straight arm running from the centre out are set apart from each other, at a disto the jet-pipe, if the area of the cross sec tance equal to the depth of the arms,

water.

ON THE MOTION OF A FALLING ARROW
OR DART.

with curved division pieces to form the upper inclined surfaces of the blades dd,
sides of the arms, and jet-pieces fixed and assist in keeping up the motion of
betwixt the plates; the main shaft is the machine. Thus, one part of the
fastened to the centre of the uppermost force which keeps the machine in motion
plate, and the opening for the water is in is derived from the momentum given
the centre of the plate which is under to the water by the pressure of the
most. If the arms or water spaces are column of water which is above the under
beyond a certain width, the inner ends of end of the main pipe, and another part
the divisions placed betwixt the plates, of this force is obtained by the weight
will terminate in a sharp end before they of the water after it gets into the part
reach the central opening. Betwixt the b b, c c.
inner ends of the division pieces and the The hydraulic engine we have last de-
central opening, the top and bottom plates scribed is an improvement on the well-
should be formed, in such a manner as to known machine called the “Danaide;"
allow the water to flow from this opening the principal difference in the two ma-
out to the inner ends of the arms, at every chines is, that, in the “Danaide,” the
point of its passage, with the same, or plates or blades which the water acts
nearly the same degree of speed. This against are straight, and have a vertical
is managed by diminishing, from the position, while, in the new machine, the
central opening out to the inner end of blades run from near its top end to the
the arms, the depth of the space which opening below, in an angular or spiral
is betwixt the top and bottom plates. a a direction.
is part of the main shaft; the arms or
passages for the water are marked bb;
and c is the central opening for the
Another machine, differing more ma-

BY CAPTAIN J. NORTON. terially from the first, is represented in

Sir,- It has frequently occurred to figs. 6 and 7.

me, when a school-boy, practising with In this machine the main pipe, a a,

an arrow or dart of a peculiar form, that conducts the water from the reservoir the arrow, in descending, after being bb; cc is the rotary part of the ma

thrown or shot perpendicularly into the chine; this part is open at the top end, air, instead of coming down with its bb, where the water is admitted, and it point foremost, has turned on its side, has an opening at c c, its bottom end, to and come to the ground spinning horiallow the water to escape after it has zontally, so as to resemble the wheel of acted on the machine. To the inside of a jack. The arrow, which in its ordinary 6 b, c c, the plates or blades marked d d fall would reach the ground in the space are fixed. These plates run from near

of a second, by this rotary motion in a the top of b b, c c, to the opening below, horizontal line occupies full a minute in in a spiral direction, as shown in the its descent. I mention this fact in the figures. The main shaft or spindle, e e, hope that some of your numerous readers is fixed to the blades, and to the part

may be so good as to explain the cause, b b, cc, in the manner shown in fig. 7,

as, in the event of the art of flying ever in order that the motion which will be coming into fashion, a knowledge of the given to the part b b, c c, by the action cause of the arrow performing the hori. of the water on the blades, may be com

zontal motions of a wheel may be of municated to the shaft e e. The bottom practical use. The arrow I allude to was end, or foot, f, of the shaft turns in

in the form of a flat spoon, having a brasses, in the ordinary way, and its top

notch about its centre, where it was end has a bearing at g. It will now be found to balance, inclining towards its clear, that if the water be allowed to rush point, and was cast by means of a pliable from the main pipe a a into the part bb,

stick, having a string at the end of it; cc, it will, by its force against the blades,

a knot in the string fitted into the notch, set them, and the parts in connexion

and by bending the stick the arrow was with them, in motion ; but the weight of

discharged. the water will, during its descent along

Yours, &c., the spaces marked h h, also act upon the

J. Norton.

MR. ZANDER'S TABLES OF THE SIX STEAMERS PLYING ABOVE BRIDGE. Sir,--The interesting notice of Mr. sions given of the Era's paddles-length Zander's

's steam expansion and condensing of the boards 5 feet, breadth 1 foot; num. systems in the two last Numbers of your ber in each wheel 12 ; number of pad. valuable journal is accompanied by two dle boards immersed in the water in both useful comparative tables of the dimen wheels 5. Area of paddle-boards in both sions and performances of sundry steam wheels, or total effective paddle surface boats; but in those tables there appears 25 square feet. Now, it is to this stateto me to be an error with regard to the ment, that the effective paddle surface area of the total effective paddle-board is equal to the area of all the floats insurface of each vessel, which, should my mersed, that I wish to invite attention. view be incorrect, I hope will call forth With paddle-wheels of the foregoing a reply from some of your able corres dimensions, in order that 2} floats in pondents.

each wheel may be immersed, the dotted I will take, for instance, the dimen line of the accompanying figure must be

the water line, cutting the floats cc at But I very much question whether the one-fourth their breadth, in which case mean useful effect extends beyond the the greatest depth of immersion, a b, area of one paddle board in each wheel would not exceed I foot 8 or 9 inches, (or in this instance, of 5 square feet), for which, multiplied by the breadth of the supposing the common paddle-wheel can wheel (5 feet) gives an area of effective be beneficially immersed to the depth paddle-board surface for each wheel of a b of the diagram, its efficiency would 84 square feet, or 17} feet for both wheels, be greater, by the direct action of boards instead of 25 feet ; for I cannot conceive of the same depth at a b, than by the that the boards immersed and moving oblique action of those in the position behind each other so rapidly exactly in If I am correct, several of the calthe same plane, increase the area of re culations in the tables referred to, would sisting surface which each presents, but require reconsideration. merely maintain a constant action upon I am, Sir, your obedient servant, that area, as each board rises out of the

“ B. B." water in succession.

October 27, 1842.

MR. MARTYN ROBERTS'S IRON BATTERY FOR BLASTING ROCKS BY GALVANISM.

Sir, It gives me great pleasure to find a little power, in order to obtain the adthat my process of blasting by galvanism vantages I have before mentioned. has been so successfully employed by On reference to my pamphlet on the your able correspondent “ W. C.;" and, subject of blasting, it will be seen in on reference to the account of the opera what manner the power to overcome obtions at Dunbar Harbour, quoted in your stacles, or convey the electricity to a dis1000th Number, he will see that the si tance, and that to act upon bodies, can multaneous explosions on my plan were severally be obtained, without increasing there most effective.

the complexity of the apparatus. (See The iron blasting battery “ W. C." pp. 25 and 26.) The batteries I recomwishes me to describe, I contrived in or mend for the use of workmen consist of der that the cost of the apparatus should twenty plates of iron, (copper may be be reduced as much as possible, that its substituted if preferred,) and twenty arrangement should be of the most simple plates of zink, each 7 inches square. The kind, and that but little trouble should thickness of the plates is immaterial: the be needed in setting it at work or keep iron need not exceed 15 or 20 ounces to ing it in order. Iron, as a material for the square foot. A wooden frame is the negative plate, is not only much made to receive these plates ; the sides cheaper than copper, but is also more ef of the frame are bars, and the ends solid; fective. It is true that, under certain these ends rise about two or three inches circumstances, (such as when loaded with above the square of the top of the plates, rust,) it is less efficient; but when mode for the purpose of supporting the apparately clean, and excited by dilute sul ratus for making contact. The bottom phuric acid, I have found it far more of the frame consists of two bars each, powerful than copper as a negative plate placed about a third of the width of the in the galvanic series, (vide my experi frame from the sides. These bottom ments on this subject, as published in the bars not only support the metal plates, Phil. Mag. for January, 1810;) and the but also the strips of wood that maintain cause of this superiority in iron I have the plates separate from each other. pointed out in a subsequent Number of the same periodical, for June, 1841.

Fig. 1. Before the iron plates are used, they should be cleaned of the dark blue oxide which has adhered to, or indeed been rolled into their surfaces by the process of manufacture they have undergone : this is best done by keeping them for half an hour in dilute sulphuric acid, or in a solution of sal ammoniac, and then giving them a dip in dilute sulphuric acid. There are no cells or partitions between the plates in this battery, and one great inconvenience is thus obviated. It is true that this arrangement prevents our obtaining the full intensity of the instrument, i. e., the power of

Fig. 1 shows the arrangement of the carrying its electric force through a great

frame. The iron and zink plates are put length of wire; but, so arranged, we into the frame alternately, that is, an iron gain portability, simplicity of construc plate is put close to one of the solid ends, tion, and perfect security against de then a zink plate next to the iron, then rangement by any clumsiness of the another iron plate, and so on, until the workman using it. I could describe a frame is filled, care being taken to finish battery of much greater power than this, the series by an iron plate. The plates but its complicated form would require are prevented from touching each other an electrician to work it with constant by strips of wood, Paths of an inch success; and I think it better to sacrifice square, and as long as the plates are

deep: two of these strips are placed be- fig. 2) passes through the solid end of the tween each plate, and their lower ends frame, and terminates in a binding screw. rest upon the bottom bars. The plates The spring of the sliding disk is of brass should be jammed sufficiently tight to wire, and the extremity not soldered to gether to prevent any motion in the strips the disk passes through the same solid of wood. The mode of connecting one end of the frame and terminates on the plate with the other requires some little outside in a binding screw; these two attention, as a mistake in this will greatly binding screws are to hold the ends of the diminish the power of the battery. I conducting wire, (sec. 46.) have endeavoured so to contrive the connexion as to obtain the action of both

Fig. 3. surfaces of every plate, and yet to avoid any cross and counteracting currents of

d electricity. Let fig. 2 represent a section of 5 pairs : let the letters indicate the iron plates, and the numbers the zink plates.

Fig. 2.
2 3 4 5

с

e

с

b

d e f Let a and 6 be joined together and stand free as a double terminal plate, or

A pole, having of course a wire proceeding from it as a conductor; then join 1 to c, 2 to d, 3 to e, 4 to f, and 5 in this series of 5 pair will be a zink plate un plate. It is needless for me here to deconnected with any iron plate, but having scribe the apparatus for making contact, a wire soldered to it going off as a con as an account of it has already appeared ductor in the usual way from the other in your pages. terminal pole of the galvanic series. In The box for containing the exciting the same manner is a series of 20 pair solution (1 part sul. acid to 16 of water) put together, and connected in the frame is generally made of $th inch plank, the as in fig. 2, by means of thick wires joints dovetailed, and set together with or strips of metal carefully soldered white lead ; this will make it water-tight. to them. The several plates are sepa The box should be about an inch longer rated each from its nearest neighbour, and wider, and two inches deeper inside by the strips of wood already described. measure than the frame of plates ; and I The plates being thus arranged, the wire have found it convenient, that the box be soldered to the double iron plate (see fig. 3) fitted with two uprights, or standards, at is fastened to the fixed disk of the appa- the sides, with a sliding pin across from ratus for making contact, described in one to the other, for the purpose of supthe pamphlet, and the wire joined to the porting the frame of plates raised from the zink plate terminating the series (as 5 in acid, and thus allowing the liquid adhering