The surface of water or other liquid is always spherical, and the greater any sphere is the less is its convexity. 
Hence the top diameter of any vessel at the summit of a mountain will form the base of the segment of a greater sphere than it would at the bottom. 

This sphere, being greater, must (from what has been already said) be less convex; or, in other words, the spherical surface of the water must be less above the brim of the vessel, and consequently it will hold less at the top of a mountain than at the bottom. 

The reader is therefore free to select any mountain he likes in Italy—or elsewhere!