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have at one and the same time both a front and back stroke given to them (though not in the same plane). There are also loose stripping bars with guards, which, besides regulating the depth to which the heckles or brushes shall penetrate, doff the tow from the brushes and heckles; and two smaller cylinders, b2 62, fitted with brushes for cleaning the working brushes and heckles, c and c'. Rotation is given to the rotating parts of this machine in the same way as to the rotating parts of the one before described. But the holder is made to traverse or move forward in the trough by a combination of a bell-crank movement with the rising and falling motion of the trough, as afterwards described. A view of the sort of holder preferred for this machine is given separately, on an enlarged scale in fig. 56 (a side elevation), fig. 6' (a cross section), and fig. 7' (a longitudinal section). It consists of two plates, No. 1 and No. 2, connected ransversely by a screw-bolt, S, and having flanges, AA, at their upper edges, by means of which they are supported in the trough (h). The plate No. 2 has two flanges, BB, one on each side, which come within the flanges, AA, of the plate No. 1, and thereby confine the streak of flax or other fibrous material at the edges. The inner face of the plate No. 2 is planed perfectly true, and covered with felt, cloth, or some other soft or yielding material; but the plate No. 1 is made on its inner face with flat beads (C), and flat grooves (D), in alternate order, so that the streak of flax or other material may be thereby the more firmly compressed and held between the plates, without being unduly crimped. At their under edges (E), the plates are chamfered off as shown, so as to admit of the holder coming close down upon or within the nip of the brushes or heckles affixed to the revolving cylinders. It will be observed that, by this mode of construction, the pins or studs ordinarily made use of, to confine and regulate the outer edges of, the streaks are wholly dispensed with, and a greater breadth of area thereby obtained whereon to spread the streaks, while at the same time the holder is narrowed, and rendered lighter and more easy to work.

The mechanism for lifting the trough is shown in fig. 26, and consists of a combination of pinions (k2 k3), wheels (m n), cam (p), straps (0), pulleys (g), and levers (ra), such as is ordinarily used in heckling machines, and well known. When the trough is raised, it pushes up a rod, z, which is connected to the long arm of a bell-crank, y, mounted on a standard affixed to the top of the framework, a, when a weight, W, which is attached to the opposite end of that long arm, falls over, and causes the short

arm of the bell-crank to pull in a rod, z1, which draws forward a finger-bar, x (of the ordinary construction), to an extent sufficient to advance the holder the breadth of one set of heckles or brushes. The tow and shive and dirt doffed from the heckles and brushes are, in this case, reccived upon an endless chain of bars, tt (instead of the inclined grating used in the machine first described), which bars extend the whole length of the machine under the heckles and brushes, and are connected together by two side bands, tt. The chain of bars revolves round two friction pulleys, vv, and takes into two pinions, u u (one on each side), by means of which pinions rotation is given to the chain from the same first mover by which the other parts of the machine are put in motion. The shive or dirt falls through between the bars on to the floor, while the tow is carried forwards on the top of the bars, and delivered into the trough, T. To separate the tow doffed from each set of heckles or brushes, from that doffed from the others, the space between the top of the endless chain of bars and the heckle and brush cylinders is divided by partitions, aa aa, fig. 1', into as many compartments as there are sets of heckles or brushes, and the receiving trough, T1, is also divided into a corresponding number of compartments.

(To be continued.)

THE LINES OF THE CANOPUS." Sir,-Many thanks to your correspondent "Z," for his remarks on Art., p. 177, relative to the Canopus. He has the advantage of me, as I never saw the Canopus in dock, but I have seen her lines, and believe her midship section not to be very different from what it is represented to be in fig. 4—at least from the water-line to 15 feet below it, which is all that affects my data. And though it were not, my argument would not be affected. Some of her sections before the middle are such as are described by "Z."

According to the assumption in the text, s s is 15 feet below the load waterline, but for the same reason that 'r', fig. 8, (Vanguard) is not taken as giving an estimate of the stability, but n'n', which is a mean point between s and B'; so a mean point between 8 and B in the Canopus should be taken as giving an estimate of her stability. It is to the breadth there that "a shade less" is meant to apply, and not to the breadth at ss, which no doubt would be much less; but it would be very much less

in Vanguard at s' s', fig. 8, and still less if the curved floor, complained of, were straight. Fig. 4 and 9 are intended to be similar.

The positions of a' b' a" b", and in fig. 5 and 6, are respectively 10 feet, 7ft. 6 in., and 4 ft. 6 in. below the load water-line under the circumstances stated. In these vessels, however, the positions would vary with the direction of the sea as regards the course of the vessel; and their positions in other vessels would depend upon their breadth, and the direc tion of the sea, together with its height and length.

But I speak of the Canopus family and Vanguard family, being more anxious to establish the truth of the principles than the absolute fact, as regards the particular ships-the latter indeed could only be obtained from a knowledge of all the sections of each. The midship sections, however, and sufficient to argue upon, as to the relative value of the respective principles of construction displayed in each.

While I do not know any forms so bad, in this respect, as those designed by Sir William Symonds, I do not mean to say that there are not others very bad. Amongst these I would class the Gibraltar, the Raleigh, the Inconstant, and some few French, of which it is needless to speak; these vessels cannot fail to roll deeply in a seaway.

I did not select the Canopus as having the best form in the part alluded to, but as being of the same class as the Vanguard. Some of the old English and American forms are better in this point, than her, but there would have been a difficulty in finding one of their class in the Vanguard family to compare them with.

The points sought to be established are-that in proportion as the stability is obtained by great breadth, and a V shape of midship section, there will be less comparative stability and ease of motion in a seaway and strong winds-those circumstances under which they are most necessary.

The greater the breadth, the greater must be the perpendicular depth of side below the load water-line to retain stability and the greatest comparative ease in a seaway.

The desirableness as regards ease, and also expense, of deriving part of the stability from ballast.

The desirableness of centralizing the weights (literally at least), and the difficulty of doing so from the weight of the sides and guns being greater than that of the moveable weights, and as this difficulty increases with the breadth (all other things being equal) the ease will decrease with the breadth in the respective classes.

Very truly yours, Sir,

E

ON THE APPORTIONMENT OF THE COST OF EARTH-WORK IN FORMING EXCAVATIONS, EMBANKMENTS, ETC. BY T. SMITH, ESQ.,

C. E.

Sir, The investigations on the removal of earth by Monge, and Dupin, although characterized by a refinement of thought apparently but ill-adapted to the usually rough details of actual practice, are, nevertheless, interspersed with many valuable hints, which, with a little modification may be turned to important uses by the practical man. In the application of the theory as developed, it is true, that an ultimate atom, or an indefinitely minute particle of the mass, may seem to be but a dim representative of the cubic foot or yard of practice; yet an analogy really exists between them, which, when used within certain limits, leads to results that may be regarded as practically correct in our every-day operations, and readily applied to some of the useful purposes of real life.

To those who may enter upon the study of this interesting subject, I think it will appear at an early stage of their progress, that by adopting the method of moments as taught in elementary works upon mechanics, the problem becomes considerably simplified and divested of much of that abstract character which not unusually shrouds the reasonings of eminent analysts. It is not my intention, however, in this paper to enter upon any discussion of the general theory; my object being merely to indicate its application to a particular case, namely, the apportionment of the cost of work in the various parts of the same section of an excavation, embankment, &c.

If P pence be the average price per cubic unit fixed for the excavation and removal of the material in a cutting, the cross section of which is represented by fig. 1, it is clear, assuming the labour of