Sure, it's all relative (really bad pun). You are right about the
relative changes and what you are thinking describes how glass
thermometers and mercury barometers actually work. You have a large
pocket of liquid attached to a relatively thin column on top. The
relatively thin column shows the change in volume better and makes it
easier to see.

The cylinder was cylindrical, it's made for general measurement of
liquid volumes. There is a more accurate device called a volumetic
flask that works on the principle you describe, but it's only
calibrated at one point. I have one for 100 ml. That is too small to
use here, the changes would be tough to see.

Joe

rmed (Brewser83) wrote in message >...
> Joe,
>
> Great experiment. I am assuming that the cylinder you used was, well,
> cylindrical. Would not the volume of one inch of wine in the body of the carboy
> (say 10 inches in diameter) be significantly more than one inch of wine in the
> neck (say 1 inch in diameter)? Thus the change in height would be greatly
> multiplied in the neck of a properly topped carboy. All my carboys are filled
> at the moment. I will try some experiments in a gallon jug.