90 
MR. F. E. SMITH ON THE ABSOLUTE MEASUREMENTS OF A 
clear from the small diagram at the top of fig. 22. One brush made contact with 
one (or two) segments on each disc and the circuit was completed through the rotating 
conducting wires. The displacements were read to O'OOl mm. and the changes in 
i5 
CQ 
uJ 
> 
tr 
D 
o 
UJ 
_l 
< 
O 
in 
lO 
i 5 
20 
IO 864202 468 lO 
DISPLACEMENT IN MILLIMETRES 
Fig. 22. 
A, change (parts in 100,000) in voltage induced by rotation of radius R due to displacement of 
cylinder in direction perpendicular to its axis; B, change in mean voltage induced when five 
brushes are used, touching points 72 degrees apart on edge of disc. 
potential were calculated from the changes in the galvanometer deflection which were 
produced on reversal of the current in the coils. 
A displacement of 10 mm. increases the difference of potential between O and B\ 
