So far we have spoken only of light; but hold your hand in the sun, and feel the heat of the sunbeams, and then consider if the waves of heat do not do work also. There are many waves in a sunbeam which move too slowly to make us see light when they hit our eye; but we can feel them as heat, though we cannot see them as light.
The simplest way of feeling heat waves is to hold a warm flatiron near your face. You know that no light comes from it, yet you can feel the heat waves beating violently against your face.
Now, there are many of these dark heat rays in a sunbeam, and it is they that do most of the work in the world. It is the heat waves that make the air hot and light, and so cause it to rise, and make winds and air currents; and these again give rise to ocean currents. It is these dark rays, again, that strike upon the land, and give it the warmth which enables plants to grow. It is they also that keep up the warmth in our own bodies, both by coming to us directly from the sun, and also in a very roundabout way through plants.
Coal is made of plants, and the heat it gives out is the heat these plants once took in. Think how much work is done by burning coal. Not only are our houses warmed by coal fires and lighted by coal gas, but our steam engines work entirely by water which has been turned into steam by the heat of coal fires; and our steamboats travel all over the world by means of the same power.
In the same way the oil of our lamps comes either from olives, which grow on trees, or from coal and the remains of plants in the earth. Even our tallow candles are made of mutton fat, and sheep eat grass; and so, turn which way we will, we find that the light and heat on our earth, whether it comes from fires, or candles, or lamps, or gas, is equally the work of those waves of ether coming from the sun, which make what we call a sunbeam.
—From "The Fairy Land of Science," by Arabella B. Buckley.