In order to make the experiment more attractive, and besides, to be used as a ballast, a small figure is hung from the bubble, which has a hook to make hitching easier. Sometimes the hook is hollow and it is the very place by which water goes into the bubble. It’s the case of the little devils represented in Wolff
(1722), Tümming (1725), Musschembroek (1739) and Brisson (1781).
On other occasions the bubble has a hole or intake in its side, like the cases of De La Fond (1767; 1775), Deschanel (1869) and Drion et Fermet (1869). Other similar representations, which don’t show the way water goes into the bubble, are found in Roret (1834) and Bird (1848). Tissandier (1883) depicts a bubble made from an empty walnut shell.