Suspending snail shells from pieces of string while sipping wine is a good way to spend a quiet Saturday evening at home. Only a few would disagree, I'm sure.
There is a deeper motive behind this activity, of course. I am trying to figure out where the centers of gravity of the shells are located.
Here is a marine gastropod shell hanging from a string with the columella (central axis) of the shell approximately horizontal (I don't know what the species is).
Here is another unidentified marine gastropod in suspension.
Finally, a land snail, a Cerion sp.
From the photographs, I've estimated the relative location of the center of gravity for each shell. The numbers from the base of the aperture and expressed as a fraction of the total shell length were as follows: 1st species, 0.37; 2nd species, 0.46; Cerion, 0.52.
Keep in mind that these numbers are from a single specimen for each species. There will undoubtedly be some within species variation.
I don't yet know what these number mean in terms of the shape of each shell. Various decorations present on some shells, for example, the spines along the lip of the 2nd shell, must also influence the location of the center of gravity. Also, the location of the center of gravity will probably be different when a shell is occupied by a snail.