> > My recommendation for the problem of sinkage or floatation of the ball
>is
>to
> > make it such that it floats, but only barely.  Say, with a specific
>gravity
> > of 0.90 to 0.95 or so.  This will prevent it from getting hung up on
> > obstacles above the water (the ball will simply get knocked downwards
>into
> > the water for a short time), while keeping it off of any submerged
> > obstacles.
>
>This will get caught in the first pool that has an outlet under the water
>surface.  Such things are common in caves.

This is correct, of course.  Someone else mentioned this.  I didn't consider
hidden pools.

But I also don't consider any of the mechanical squeezers viable options,
either.  Provided that this is battery powered, constantly changing the
pressure with a servo/piston would consume much power, particularly since
the 8-mile journey will likely take several weeks to occur, if at all.  And
if you put a 2-hour time frame on pressure changes, it may take days or even
weeks just to get past a 100-yard section filled with obstacles.

Remember, earlier in this thread people were suggesting using low power PICs
and shutting everything off between samples just to conserve a few
microamps.  Now you're talking several hundred milliamps to operate your
pressure system every 2 hours over what's likely a several-week period of
time.

I don't know what the size of this underground spring is, but I don't think
we're talking "Old Faithful" here.  Generally, they're more like a slight
trickle through a series of small cracks in the soil.  I could be wrong,
though.  Even artesian wells only fill very slowly.  I don't think there are
any 2" diameter channels through the earth for the water to travel.

--Andrew

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