PROFESSOR T. A. HEARSON ON THE KINEMATICS OF MACHINES. 
29 
slot way to remain, constantly equal to the diameter of the pin, as shown in fig. 4. 
The centre of curvature of any portion of the slotway where the pin w is momentarily 
situated being y, the instantaneous relative motion of the parts will be the same as 
would be due to a four-linked mechanism of which the centres of the pins are at s, u, 
w, y. When the pin w moves to a place where the curvature is different, the relative 
motion will be the same as that due to a four-linked mechanism in which the lengths 
of X and Z are different from what they were previously. 
If, in figs. 1, 2, 3, 4, the lines joining the centres y, w and s, u are produced to meet 
in the point r, it may be readily shown that 
The angular velocity of Y . . . m sr 
ThfTangular velocity of Z re,atlve b' *»? = -. 
In the next consecutive position of the mechanisms 1, 2, and 3. the position of the 
point r will have changed, and with it the angular velocity ratio. In mechanism 
fig- 4, it will be possible, by a suitable curve for the slotway, for the intersection of 
the two lines to remain at a fixed point for a limited amount of motion, when, during 
