Science Primers, Introductory

by Thomas Henry Huxley

The water, we see, fills the cavity of the tumbler for half its height, therefore it occupies that much space, or has that bulk or volume. If you put the closed end of another tumbler of almost the same size into the first, you will find that when it reaches the water, the latter offers a resistance to its going down, and unless some of the water can get out, the end of the second tumbler will not go in. Any one who falls from a height into water will find that he receives a severe shock when he reaches it. Water therefore offers resistance.

If the water is emptied out, the tumbler feels much lighter than it was before; water, therefore, has weight.

And, finally, if you throw the water out of the tumbler at any slightly supported object, the water hitting against it would knock it over. That is to say, the water being put in motion is able to transfer that motion to something else.

All these phenomena, as things which happen in nature are often called, are effects of which water, under the conditions mentioned, is the cause, and they may therefore be said to be properties (§ 4) of water.

All things which occupy space, offer resistance, possess weight and transfer motion to other things when they strike against them, are termed material substances or bodies, or simply matter. Water, therefore, is a kind, or form, of matter.

15. Water is a liquid.

You will easily observe that, though water occupies space, it has no definite shape, but fits itself exactly to the figure of the vessel which holds it. If the tumbler is cylindrical, the contour of the surface of the water will be circular when the tumbler is held vertically, and will change, without the least break or interruption, to more and more of an oval when the tumbler is inclined, and whatever the shape of the vessel into which you pour it, the sides of the water always exactly fit against the sides of the vessel. If you put your finger into the water you can move it in all directions with scarcely any feeling of obstacle. If you pull your finger out there is no hole left, the water on all sides rushing together to fill up the space that was occupied by the finger. You cannot take up a handful of water, for it runs away between your fingers, and you cannot raise it into a permanent heap. All this shows that the parts of water move upon one another with great ease. The same fact is illustrated if the tumbler is inclined so that the level of the surface rises above the edge of the tumbler on one side, and the water is therefore to some extent unsupported by the tumbler at this point. The water then flows over in a stream and falls to the ground, where it spreads out and runs to the lowest accessible place, or gradually soaks up into crevices.

Nevertheless, although the parts of the water thus loosely slip and slide upon one another, yet they hold together to a certain extent. If the surface of the water is just touched with the finger, a little of it will adhere; and if the finger is then slowly and carefully raised, the adjacent water will be raised up into a slender column which acquires a noticeable length before it breaks. So, in the early morning, after heavy dew, you may see the water upon cabbage-leaves and blades of grass in spherical drops, the parts of which similarly hold together.

Material substances, the parts of which are so movable that they fit themselves exactly to the sides of any vessel which contains them, and which flow when they are not supported, are called fluids, and fluids the parts of which do not fly off from one another, but hold together as those of water do, are called liquids.

Water therefore is a liquid.