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axles and oiled pivots. But I choose the liquid gyrostat at present 
merely because it is more easily described. 
6. Imagine a hollow anchor ring, or tore, that is to say, an endless 
circular tube of circular cross-section. Perforate it in the line of a 
diameter, and fix into it small straight tubes to guard the perforations 
as shown in the accompanying diagram. Fill it with frictionless 
liquid, and give the liquid irrotational circuital motion as indicated 
by the arrow-heads in the diagram. This arrangement constitutes 
our hydrokinetic substitute for a mechanical fly-wheel. Mount it 
on a stiff diametral rod passing through the perforations, and it 
becomes the mounted gyrostat, or Foucault gyroscope, required for 
our models. Its use would have considerably simplified and 
shortened the description of a model communicated to the French 
Academy last September,* which, however, was given purposely 
in terms of the Foucault gyroscope because it thus describes real 
mechanism by which the exigencies of the model can be practi- 
cally realised in a very interesting and instructive manner, as 
may be seen in §§ 3-5 of Article C. of my Papers, and in my 
Address to the Institute of Electrical Engineers of 10th January 
1889. 
7. Let XOX', YOY', ZOZ' be the three bars of the G frame : 
mount upon each of them four of our liquid gyrostats, those on 
Comptes Bendus, 16th September 1889 ; Art. C. of Papers, Yol. III. 
