of the square A, entering into a round hole in the centre of the square B.

Clutches or glands may be used with much advantage as a coupling for double bearings. Fig. 57 represents a coupling of this kind; it consists of two crosses, A A and B B, one fixed to each shaft: BB has its ends bended forward, and lays hold of A A, which turns that shaft round.*

In boring-mills two kinds of clutches are used. The one for the smaller kinds of work is represented in fig. 58. A B is a round plate of cast iron fixed firmly on the shaft C; DE a lever fixed to the shaft H by the bolt F, and capable of being moved in the direction of the plate AB, so that it can lay hold of the projections G GGG, which will admit the boring shaft H to be thrown in and out of geer at pleasure.

The second kind of boring-mill clutch, or the one that is used to bore the largest cylinders, is represented in fig. 59. The only difference between this clutch and the one just described, consists in having the lever DE to turn on a bolt at F in a cast iron plate I K L, instead of hanging from the shaft H. Three spare sets of ears, which are cast on the plate, to be used in case of those in action breaking, support the lever near the point of pressure, and take the stress entirely off the bolt F.

When an engine is started, it frequently happens that the crank is on the wrong side of the axis of the fly-wheel, so that both that and the shaft make one or two, and, if the attendant is negligent, several, revolutions in the wrong direction. To prevent the mischief that would accrue from such an occurrence, a coupling, as is represented in fig. 60, is introduced. A and B are two vertical shafts, maintained in the same line by a small circular pin, which passes from the shaft B into a cavity on the shaft A, which cavity is large enough to admit the pin to lay in it without communicating motion to the shaft A. The shaft B, which is connected with the moving power, has a coupling piece with prominences or teeth, perpendicular on the one side, and inclined on the other, fixed on its upper end. The coupling or catch box C, which is capable of sliding freely up and down the square part of the shaft A, has a correspondent set of teeth; by which it is evident, that when the shaft B turns the right way, the perpendicular sides of the teeth of the respective coupling pieces will act together, and carry round the upper

For a method of constructing glands we must refer our readers to Buchanan's Essays on Mill-work.

shaft A; but when B turns in a contrary direction, the inclined sides of the teeth of the catch-box will slide over the inclined sides of the teeth of the piece on the shaft B, and cause the catch-box C to move up and down without communicating motion to the shaft A.

Fig. 61 represents the coupling link used by Messrs. Boulton and Watt in their portable steam-engines. A, a strong iron pin, projecting from one of the arms of the fly-wheel B; D a crank connected with the shaft C; and E a link to couple the pin A and the crank D together, so that motion may be communicated to the shaft C.

Hook's universal joints are sometimes used to communicate motion obliquely instead of conical wheels. Fig. 62 represents a single universal joint, which may be employed where the angle does not exceed forty degrees, and when the shafts are to move with equal velocity. The shafts A and B, being both connected with a cross, move on the rounds at the points CE and D F, and thus, if the shaft A is turned round, the shaft B will likewise turn with a similar motion in its respective position.

The double universal joint, fig. 63, conveys motion in different directions when the angle is between 50 and 90 degrees. It is at liberty to move on the points G, H, I, K, connected with the shaft B; also on the points L, M, N, I, connected with the shaft A: thus the two shafts are so connected, that the one cannot turn without causing the other to turn likewise. These joints may be constructed by a cross of iron, or with four pins fastened at right angles upon the circumference of a hoop or of a solid ball: they are of great use in cotton mills, where the tumbling shafts are continued to a great distance from the moving power; for by applying a universal joint, the shafts may be cut into convenient lengths, and so be enabled to overcome a greater resistance.

OF DISENGAGING AND REENGAGING MACHINERY.

A KNOWLEDGE of the best methods of disengaging and reengaging machinery, or, as the workmen call it, throwing in and out of geer, is found to be highly necessary in most manufactories; and yet it frequently happens that the workmen are either very ignorant of, or very inattentive to, this important subject.

Matter possesses a certain property termed inertia, which has a tendency to maintain it in the state in which it actually is; that is to say, if a body is set in motion, this property has a tendency to maintain it for ever in that state, and certainly

would, were it not gradually overcome by friction, or suddenly stopped by some stronger power; the same may be said of a body in a state of rest, as this property would ever maintain it in that state, were not some stronger force applied to set it in motion. Such being the case, it frequently occurs, when powerful machinery is moving with some velocity, and another part, which is out of geer, is suddenly connected with it, or thrown in geer, that the shock proceeding from inertia snaps the teeth of the wheels, or causes destruction to some other part of the machinery. To obviate this as much as possible, such means should be resorted to, as have been found in practice to answer best. The risk of breaking the teeth may be considerably lessened by first setting the wheel, that is to be thrown in geer, in motion by the hand.

The methods that have been adopted for throwing machinery in and out of geer are various; some of the principal of which we shall now proceed to notice.

Fig. 64 represents the sliding pulley. Pa pulley, having a hollow cylindrical bush made so that it can revolve easily upon the axle and slide backward and forward upon it; Ba part of the bush projecting on one side of the pulley, having a groove sufficiently large to admit the lever L to lay in it without impeding its motion; CG a cross or gland fixed firm to the axle; and I, one or more teeth, projecting from the pulley on the side opposite to the bush. When the axle AD is required to be put in motion, the lever L must be moved towards the cross or gland CG, so that the teeth upon the pulley may catch hold of and carry it round with it. The fast and loose pulley is represented in fig. 65. B is a pulley firmly fixed on the axle A, and C a pulley with a bush, so that it can revolve upon the axle A without communicating motion to it. This contrivance is remarkable for its beautiful simplicity, as the axle A can be thrown in and out of geer at pleasure, without the least shock, by simply passing a strap from the one pulley to the other.

The bayonet, in its construction, somewhat resembles the sliding pulley. It is shown in fig. 66. A is a pulley or binder, connected with the moving machinery by means of a strap, and revolving upon the horizontal shaft B C, which is out of geer; DE is a pulley or wheel, made of either metal or wood, fixed firmly to the horizontal shaft, and having two holes to allow the legs of the bayonet to pass through; FG is the bayonet, having a bush, and capable of being moved

D

backward and forward upon the horizontal shaft by pushing the handle HH; so that when the shaft BC is required to be put in motion, the attendant has only to push the bayonet into the pulley D E, which will immediately carry it round.

Fig. 67 represents one of the simplest ways of disengaging and reengaging wheels. A B, the bridge of the wheel, No. 1, acts as a lever, having its fulcrum at A; the other end of the bridge B is capable of being lifted by the key KK. When the wheel, No. 2, is required to be thrown out of geer, the key K K is pressed downwards, and the end of the bridge B rests upon the extreme end of the key, as shown by the dotted lines.

The tightening roller is represented in fig. 68. A and B are two pullies, the one to receive, and the other to transmit, motion, by means of the strap C: D is the tightening roller, fastened to a movable arm E, and connected with a lever GF. When the moving pulley (suppose A) is required to give motion to the other pulley B, the lever GF must be pushed downwards, which will tighter the strap by placing the tightening roller in the position represented by the dotted lines, and cause the pulley A to carry the pulley B round with it.

The friction clutch, represented in fig. 69, is used to disengage and reengage machinery, when the velocity of the moving parts is very great. A is a pulley, having a bush, and revolving freely on the shaft SS: B is another pulley, having a similar bush, and also capable of revolving on the shaft: CC is a dish-spring, secured in its place by the pin pp, and forcing the pulley B against the collar D, which is fixed permanently to the shaft. When motion is required to be communicated to the shaft S S, the pulley A is moved towards the pulley B, and the teeth projecting from the side of the pulley A, clasps those of the pulley B, and carries it round with it; and the friction of the pulley B against the collar D, gradually overcomes the inertia, and carries the shaft and connecting machinery also round.

The friction clutch, represented in fig.70, is a very excellent contrivance, as it prevents all those injurious shocks which the machinery is apt to receive upon being thrown into geer. CC is a cross fixed firm on the moving shaft A; and E is a pulley or drum fixed firm on the shaft to be moved, B. When the shaft B is required to be moved, the clutch or bayonet K is made to pass through the arms of the cross C C,

and clasp the screw-hoop II, which is by that means carried round with the shaft A, and the friction caused by the screwhoop II, turning upon the drum or pulley E, causes the drum and the shaft B, to which it is attached, to turn likewise.

The friction cone is very similar in its effects to the friction clutch. On the moving shaft A, fig. 71, is fixed a cone C; and on the shaft B is another cone D, made to fit in the cone C. The cone D is movable on a square part of the shaft B, and may, by a lever, be moved in and out of geer. When the cone D is moved forward, the cone C receives motion by its internal surface.

In fig. 72 is represented the self-disengaging coupling. Two shafts, A and B, have each of them a cast iron wheel, with four oblique wrought iron teeth; but the wheel on the shaft B is movable, on A it is fixed. When the coupling is engaged, the teeth of the wheel C lay hold of the teeth of the wheel D, and carry it, and the shaft A, round with the shaft B. EFG is a bent lever, having its fulcrum at F, which, during the ordinary stress on B, keeps forward the bayonet C, by the weight of the part FG; but when a more than usual stress comes on the shaft B, the pressure on the oblique teeth forces the bayonet back, and disengages the coupling, and the lever is held by a catch until the coupling is reengaged by the hand of the workman.

ON EQUALIZING THE MOTION OF MACHINERY.

THE regulation of the velocity of a mill is a matter of very great importance to preserve an uniformity of motion, either when the force of the first mover is fluctuating, or when the resistance or work of the mill varies in its degree: either or both of these causes will occasion the mill to accelerate or diminish its velocity; and in many instances it will have a very injurious effect upon the operations of the mill. Thus, in a mill for spinning cotton, wool, flax, &c., driven by a water-wheel, are a multiplicity of movements, many of which are occasionally disengaged, in different parts of the mill, for various purposes. This tends to diminish the resistance to the first mover, and the whole mill accelerates. Or, on the other hand, the head of water, which drives the wheel, may be liable to rise and fall suddenly, from many causes, which great and rapid rivers are subject to, and cause similar irregularities in the speed of the wheel. For such cases judicious mechanics have adopted contrivances, or regulators, which counteract all these causes of irregularity; and a large mill, so regulated, will move like a clock, with regard to its regularity of velocity. These