Demonstrations. Make one end of a small brass wire very sharp, and bend it into the form of a hook. Put the hook into a glass of clean water so that the point shall be below the surface. Bring the point of the hook up to the surface, and observe that the point, before breaking through the surface, lifts it as if it were a thin flexible blanket stretched over the water. Observe that the reflection seen from the surface of the water is distorted at the point where the hook lifts the surface.
Bend a wire into the shape shown at A (Fig. 1). Place a sewing needle in the hook and lay it carefully upon the surface of clean water, and the needle will float in a little depression upon the surface, as shown in the lower part of the figure. If the needle is placed below the surface, it will sink at once.
NOTE. - In all experiments on liquid surfaces great care must be taken to keep the water, and everything that comes in contact with it, clean. The touch of a greasy finger is enough to change the surface tension of the water.
Certain insects make use of the above phenomena and are able to run over the surface of water, their feet resting in depressions in its surface just as the needle does.
