270 A. BUYD. 
The cast iron frame carrying the spindle is held very 
rigidly by four $ inch bolts to a cast iron bed-plate bolted 
to a concrete foundation 5 ft. by 24 ft. by 5 feet deep, 
weighing 35 tons. This foundation was quite independent 
of the foundation and fioor of the building, so that no 
ordinary vibrations in the adjoining floor could be detected. 
Hxtreme care was taken in the turning up of the wheels 
as the accuracy of the results depends on this very largely. 
The top of the spindle was carefully faced up so as to 
present an even surface for the prism. Special care was 
taken in balancing all the rotating parts, and, on resting 
the spindle with all attached parts on a pair of horizontal 
knife-edges, no tendency to move in any position was 
noted. 
In all the flywheels tested in these experiments, the rims 
were of rectangular section, and the arms were of similar 
and approximately equal cross section all along to avoid 
difficulties in calculation. For reference, the wheels are 
lettered according to a kind of Bow’s notation e.g. for the 
three armed wheel (fig. 28), the letters A, B, C denoting the 
bays, and AB, BC, CA denoting the arms, while points on 
the rim between the arms are referred to as C. 15°, O. 30° 
and so on, the angle denoting the distance from the arm 
measured clockwise. The dimensions of the wheels were 
very carefully determined, those of each arm being given 
separately in order that any want of symmetry may be 
shown. The cross-section of the arms was approximately 
a rectangle with semi-circular ends. Hach arm was 
measured near the boss, at the centre and near the rim. 
The rim was measured near the arms and at the centres 
of the bays. The average values are given in the following 
table :-— 
