No, It is absolutely correct.

Buoyancy is the force imposed on an object by the surrounding medium.  It 
is frequently stated as: "an object is buoyed up by a force equal to the 
weight of the medium displaced by the object".  This is a function solely 
of the volume of the object and the density of the fluid.  The density (or 
weight) of the object is not a factor.

What you are thinking of is the resultant weight.  This is result of adding 
two forces: buoyancy (usually with a negative sign) and gravity.  The 
original poster was not looking to add weight, he was looking to reduce the 
buoyant force of the canister, and hence reduce the total weight he had to 
carry.  This cannot be done be reducing the air space inside a rigid 
canister (because the density of the object doesn't affect the buoyancy) 
but only by reducing the volume.

He could reduce the buoyancy by, say, filing half the thickness off the 
outer side of the canister (not recommended), but not by filling in the 
airspace inside.

mike

At 10:57 PM 6/1/00 -0400, Drew Glasbrenner wrote:
>This is wrong.
>
>  Buoyancy is the weight of an object minus the weight of the volume of water
>it displaces. This is why a canister with batteries is negatively buoyant,
>and a canister with air or anything that weighs less than the amount of
>displaced water is positively buoyant. If he adds lead to the inside of the
>canister, it will make it more negatively buoyant.
>
>Drew Glasbrenner
>
> > The canister has a fixed amount of buoyancy as a result of its
> > displacement. FIlling it with feathers, epoxy or lead will not effect
>that.
> > You can make it heavier or lighter, but that displacement and resulting
> > buoyancy will always be the same.
>
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