Making a Paper Fish Swim
The title of this experiment suggests something rather wonderful, indeed, for it seems impossible to impart motion to a paper fish.
It may be done, however, and quite easily, as will be seen from the following.
From a piece of ordinary paper cut out a fish like that shown in the [diagram], and of the size of an ordinary fish. In the center make a circular hole (A), communicating with the tail by a narrow canal. (A B) ([Fig. 11]). Having done this, fill an elongated vessel with water, and place the fish on the surface of the liquid in such a manner that the underneath face is completely moistened, while the other remains quite dry.
Fig. 11.—The swimming paper fish.
You are now ready to set the fish in motion; but to add to the interest of the experiment, challenge any of your friends to make the fish move without touching or even blowing upon it.
This may seem to them impossible. This is how it is performed.
Fig. 12.—The swimming fish.
With great care pour one large drop of oil into the opening (A); the oil at once tries to spread over the surface of the liquid, but that is only possible if it escapes by the narrow passage (A B).
This it does, and owing to the reaction the fish is thrust in the direction opposite to the flowing of the oil—i.e. it will be thrust forward, the movement lasting long enough for the spectators to view with astonishment the unusual sight of a paper fish swimming ([Fig. 12]).