It is a well known, but a not less remarkable fact, that if the tip of
an exceedingly small tube be dipped into water, the water will rise
spontaneously in the tube throughout its whole length.
This may be shown in a variety of ways; for instance, when a piece of sponge,
or sugar, or cotton is just allowed to touch water, these substances being all composed of numberless little tubes, draw up the water, and the whole of the piece becomes wet. It is said to suck up or imbibe the moisture.
We see the same wonderful action going on in nature in the rising of the sap through the small tubes or pores of the wood, whereby the leaves and upper portions of the plant derive nourishment from the ground.
This strange action is called "capillary," from the resemblance the
minute tubes bear to a hair. It is, moreover, singular that the absorption of the water takes place with great force. If a dry sponge be enclosed tightly in a vessel, it will expand when wetted, with sufficient force to burst it, unless very
strong.
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