254 Scientific Proceedings, Royal Dublin Society. 
flotation appears to me to be capable of further development, and I 
have given some thought to the matter. It is perfectly possible 
to make a tube for a Newtonian reflecting telescope (which is 
necessarily closed at the lower end) of such a weight, and with its 
weight so distributed that it will 
> not only float in water sub- 
merged to a certain point (pre- 
ferably near the upper end), 
but will be in a state of equili- 
brium when placed at any or in 
every position down to a certain 
angle, which angle depends on 
the exact outside form of the 
. tube. For instance, if A B 
(fig. 1) be a tube closed at B 
Fre. 1. and perfectly symmetrical round 
the axis A B, and the total weight of the tube be equal to the 
weight of water which is displaced when the tube is sunk to C, 
the weight of the different sections along the axis AB, can he so 
distributed that the tube will equally well remain in any other 
position, except it be so far turned over that the cylindrical 
part of the tube is lifted out of the water at one end and dipped at 
the other. 
By making the spherical part of about the proportions of the 
figure, the tube can be depressed to within 25° of the horizon, and | 
still remain in perfect equilibrium. 
Now, suppose the tube to have a pair of trunnions attached at 
the water-line, and these carried on a polar axis of, say, the English 
type (see fig. 2), we have an equatorially-mounted telescope of 
any size, without any weight whatever on the bearings of the 
Dec axis, or, the tube may be lightened by an amount nearly 
equal to the weight of the polar axis, and there will then be 
practically no weight whatever on the bearings of that axis. So 
here we have a case of, say, an 80-ton telescope mounted and carried 
by an equatorial, but without throwing any weight whatever on 
that equatorial; and the force necessary to drive the instrument is 
independent of the weight of the telescope, and dependent only 
on the friction necessary to be overcome in carrying the tube at an 
exceedingly slow rate through the water. 
AY 
So eco 
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