THE CONQUEST OF TIME AND SPACE 



pivoted on the frame B A Cy which frame is in turn 

 pivoted so that it can rotate on the axis B C. Lastly, 

 the outer frame B D C E is pivoted on the axis D E. 

 Thus the apparatus as a whole is capable of revolving 



Fig. I. 



on each of its three principal axes. But under ordinary 

 conditions it is only the inner wheel that is spinning. 

 As this wheel is perfectly balanced, it will maintain 

 steadily any position that it chances to have when it is 



[204] 



