MOTION BY BOLLING CONTACT.

49

angular velocities of the wheels are inversely as the peipendicu-lars let fall upon the common tangent from the centres ofmotion.

Fig. 52. Fig. 53.

G

73. The form of wheels, represented in fig. 52, are used insilk-mills, and in the Cometarium. The curves may be in-definitely varied, but they must always be constructed to answerthe conditions explained in Art. 72.

74. Roemer's Wheels. — e f and c n are the axes of two co-nical wheels or bevel-wheels k and G, having their verticesturned in opposite directions; the teeth of k are formed likethose of the ordinary bevel-wheel; but the teeth on G are formedby a series of pins e k, fixed on the surface of the frustum G.By varying the relative position of these pins, any given velocityratio may be obtained.

75. Various combinations have been invented for produoinga varying angular velocity; such as the eccentric crown wheeland broad pinion, the eccentric spur-wheel with a shifting in-termediate wheel, and so on.

INTERMITTENT AND RECIPROCATING MOTIONS PRODUCED BY WHEEL-WORK, HAVING ROLLING CONTACT.

76. The following is an example of an intermittent motionproduced by the continuous motion of a toothed wheel.

A driving wheel A, having sunk teeth on a portion of its edge,

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