THROWING-WITEEL8 AND Lemnas.—The essential part of a throwing-wheel ie a horizontal diec, rigidly fixed to a vertical spindle. Rotary motion may be communicated to the apindle in a variety of ways. Fig. 1111 represents probably the oldest form of throwing-wheel not turned actually by tho thrower's hand. The large wheel a ie turned by an assistant, and communicatca a vertical motion to the driving band b. By turning the band, vertical motion is converted into horizontal motion for driving the pulley d rigidly attached to the lower part of the spindle. A pedal c is shown, which is under the control of the thrower's foot, and which impends overthe driving - band. Tile pulley is conical, and by depressing the pedal, and conse quently the band, the thrower can, to a cer tain extent, regulate thespeedof the spindle, and can stop it alto gether by throwing the band off the pulley. The speed, however, is mainly regulated by signs and words addressed by the thrower to his a.ssistant. Fig. 1112 show!' a wheel which is turned by the pressure of the thrower's foot upon a large horizontal wheel, rigidly attached to the lower part of the spindle.
Figs. 1113, 1114 show respectively a throwing-wheel, and a moulding-wheel or jigger-head, both driven by steam power, and in both of which the apeed is regulated on the same principle. In Fig. 1113, motion ia communicated to the pulley G by a band running upon an overhead drum, which is driven by a steam-engine placed in any convenient position ; G revolve° in a perpendicular plane, and communicates similar motion to the large solid wheel D through the axle E ; H is a friction-wheel, which is in contact with the wheel D, and rigidly attached to the spindle B, which turns the disc C. H can be vertically raised or lowered over the face of the wheel D, by the rod R, turning on the axis L, and counterpoised by the weight S. The thrower sits on the frame A ; the motion of the wheel D in contact with the friction-wheel H causes the spindle and disc to revolve.
By depressing the weight S, the friction-wheel can be raised into a position opposite to the centre of the wheel D, and inasmuch as the speed in the centre of a wheel is less than at its circumference, the speed of the disc may be reduced. In the same manner, by raising the weight, the speed of the disc can be increased. In Fig. 1114, C is the jigger-head, and M is a stirrup, into which the operator can
insert his foot, and depress or raise the rod R. The other letters represent the same parts as in Fig. 1113. In Fig. 1115 , a throwing-wheel is shown without any seat for the thrower ; but his position is such that he can place one foot on the treadle A, which gives an oscillating motion to the cone B, which is driven by a pulley rigidly attached to its shaft, as shown. When B, which is revolving, is shifted from its vertical position, it comes into contact with the cone C, which is fixed to the spindle of the throwing-wheel. The friction of the cone B against the cone C, causes the latter to revolve. The cone B is always at the same speed, but the speed of the cone C, and consequently of the spindle and disc, can be varied at the thrower's pleasure. If the displacement of the cone B be so slight that only its small end comes into contact with the big eud of C, the motion of the spindle will be slow ; but if the displacement be increased so that the large end of B comes into contact with the small end of C, the velocity of the spindle will be greatly increased.
Fig. 1116 represents a lathe, whose speed is regulated upon the same principle as that just described. On the lathe-spindle, are fixed two cones, and running loose on a shaft parallel to it, are two other cones, revolving in opposite directions, aud driven by pulleys. When the shaft is exactly parallel to the lathe-spindle, the two sets of cones are distinct, and no motion is communi cated ; but when the shaft, together with the loose cones, is turned at a slight angle to the lathe spindle, which is accomplished by means of an turangement of levers under the control of the turner's foot, either cone can be brought into contact, and the speed be varied at will. The olcl system of applying motion to the turner's lathe, and one which unfortunately is still in vogue, is by MMUS of a largo treadle worked by an assistant, who is usually a young woman. In modern potteries, the wheels, lathes, and jiggers are, as far as possible, so arranged that they can all be driven by one endless band, passing round the whole building in which they are placed, and driven by steam power. The hand may be either above or below the floor.