CHARLES B. WARRING. 167 
_ The joints are as nearly frictionless as possible. The 
directions of the rotation of the fly-wheels are indicated 
by directional ellipses. Please to bear in mind that Sir 
William says, ‘‘ The gyrostatic system might have been 
constituted of two gyrostatic members, but four are 
shown for the sake of symmetry.’’. In other words, he 
declares that the effect would be exactly the same were 
either the right, or left hand pair omitted. This is fortu- 
nate, forin making such an instrument, the other two 
not only double the expense, but add very much to the 
difficulty of manipulation. I shall therefore content my- 
self with one pair of wheels. 
Before going further permit me to say a few words as 
to what a Gyrostat is, and how it differs from a Gyro- 
scope. Sir William Thomson invented and named the 
former. Fig. 2, represents a section of it. (The original 
drawing is shown in Nature, Vol. XV, page 297.) It is 
an ordinary gyroscopic wheel and axle enclosed in a sort 
of jacket or case, instead of being supported ina ring. 
The case answers all the purposes of the ring, but, be- 
sides, it permits a sort of circular knife edge to pass 
around the case in the plane of the wheel’sequator. The 
alalizg 
