ELASTIC RADIAL DEFORMATIONS OF FLYWHEELS. 261 
SAA 
K, knife-edge. P, prism with mirror attached. F, fixed end of distance 
rod. M, moveable end of distance rod. B B, rubber bands on crossbar. 
S, conical steel pin. G, micrometer scale in telescope. 
the mirror that the divisions of the glass scale and of the 
micrometer scale appear to be of the same size. When 
the deflection is so large that it cannot ke read on the 
telescope scale, the knife-edge is moved up or down until 
it is again visible in the field. Since the divisions on both 
scales appear of equal size, the total deflection is the sum 
of the movements of the knife-edge on the glass scale and 
the deflection as read on the telescope scale, provided that 
there is no deflection while the knife-edge is being moved. 
In flywheel measurements the deflection is sometimes so 
rapid that the rim may deflect several divisions while the 
