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to the end of the vertical axis of the wheel whose moveable 
spokes support the laminz. 
Let 7, A, P, W, be respectively the tension of thread, 
the centre, the pointer and the weight fixed to the rim of one 
lamina, and so of the others. 
To use the machine—Place a pin through the ring F so as 
to fix the ring to the centre of the graduated horizontal lamina. 
Revolve the spokes so that the angles A,RA,, A,RA,, A,RA, 
as read off on the horizontal lamina may be any selected. 
Slide out the vertical laminze until by the tension of the 
threads the weights rise so that 
ZA Wi — 2 Anas, 
ZPA,W,=2 A,RA, 
De SWE eo 2 LIAL 
But cS a SN PME 
sn PAW, snP,A,W, sin P,A,W,’ 
f’, f, T; 
‘sin A,RA, sm A,RA, sin A,RA,’ 
or the tensions of the threads are as the sines of the angles 
between the other two. Now remove the pin, and the’system 
will be found to be in equilibrium. 
(3) On a mode of propelling vessels. By J. CW: 
Eis, M.A. 
In a fish the tail is the great propelling machine, the office 
of the fins is merely to guide and balance. It is rather difficult 
to conceive this action of the tail which is able to drive the 
body through the resisting medium at such great speed. 
The single oar at the stern of a boat as used by seamen, 
or one at the side as used at Venice or in the Upper Rhine, 
produces motion in a way not altogether unlike that of the 
tail of a fish. 
