Our young scientists are still eagerly pressing onward in their search for knowledge, under the careful and sympathetic guidance of their teacher, Mr. Wilson. Step by step they have been advancing through the various stages, beginning with simple facts, either such as were evident to their own observation, or such as could be shown by simple experiment. In this way they have acquired a rich store of scientific facts, and they are now, in the higher stages, learning to offer simple explanations of these facts, and to familiarize themselves with the proper names for the various objects and operations with which they come in contact.
Last year"s course made this very evident, and it will become more so as they proceed to higher subjects. Both boys have still a scientific institute as their goal, where they mean to make their mark some day.
"I remember," said Mr. Wilson, "I began last year"s course by introducing a new word-matter. We have since then used this word, rather than speak of a substance, an article, or a body, I will now try and help you to form a clearer conception of what we mean by it. This brick lying on the table shall give us the start.
"Without taking it up, I want you to tell me all you can about it. You will, of course, begin by describing its shape, size, and color. But how did you gain this information? Your eyes told you. You learned it through the sense of sight.
"Now take the brick in your hands and shut your eyes, and you will learn something more, through another sense-the sense of touch. This tells you that the body is hard and rough. A blind man could tell that.
"But let us leave the brick and turn our attention to these two bottles. Each contains a clear liquid. The liquids are totally unlike each other, but neither of the above senses can tell us this. How can we find out? Here we have to rely upon another sense-the sense of smell-todistinguish the two bodies; this tells us that one is water,the other paraffin oil.
"We might take a piece of salt and a piece of sugar, cut to exactly the same size and shape, and it would be impossible to tell one from the other, by either of the senses to which we have already appealed. We put our tongue to each, and we learn at once what we want to know, but this time through another sense-the sense of taste.
"I think I have shown you enough to make the rest of my explanation simple. Everything around us which appeals to us in this way, through one or more of our senses, we call matter.
"By the name matter, then, we mean every substance that exists, every substance about which we may learn through our senses. The air around us is matter. We know that it has an existence, for although we can neither see, smell, nor taste it, we can hear it when it is in motion, and we can feel it as it rushes through our mouth and nostrils in the act of breathing.
"Suppose I now show you a little experiment. I have here a small piece of gun-cotton, which is a highly explosive substance. I place it in the palm of my hand and apply a lighted taper. The result is a sudden flash; the substance burns so rapidly that every particle of it disappears, and yet the hand scarcely feels the heat.
"What has become of the gun-cotton? It has not been destroyed; it has simply been converted into another form, and has passed away in the air as an invisible gas.""That reminds me, sir," said Fred, "of what we learned about the burning of the candle, the coal-gas, and the lump of coal. These things are not destroyed in the burning. They are simply changed into other forms.""Yes, my lad, you are quite right," said Mr. Wilson. "The candle contains matter in the form of tallow and wick. These substances, as well as the coal, are formed of hydrogen and carbon. The burning simply uses them to form new substances. It uses the hydrogen to form water-vapor, and the carbon to form carbonic acid gas, boththese new substances being at once absorbed into the air around.
"Nothing is destroyed. The coal and the tallow are changed into new forms. That is all.
"What happens when we dissolve substances in water? These substances disappear; they seem to be destroyed. But we know they are there still, for we can recover them easily by evaporating the water.
"It is just so with every kind of matter that exists. We may grind it into powder, dissolve it in water, and even burn it, but we cannot get rid of it-we cannot destroy it. We merely change its form; for matter is indestructible."
