Elementary

Night, the wet, the onyx-faced
Over the street was shining where
I saw an object all displaced
In black water and black air.

Was it myself? If so I found
An odd capacity for vision.
Capacity, I understand
Is limited by fixed precision,

Being the measure of displacement:
The void exists as bulk defined it,
The cat subsiding down a basement
Leaves a catlessness behind it.

That vision then, shall I concede is
Proved by a void capaciy?
What's good enough for Archimedes
Ought to be good enough for me.

But knowing little of natural law
I can't describe what happens after
You weigh a body such as I saw,
First in air and then in water.