.WONDER Why Does Steam put a Light Out?
and trees, and filling our lungs with dirt which we never get rid of. There are few things about which we are more careless than smoke, and if we had sense enough we should stop making it, even if it were only for the reason that all the stuff in smoke might be burnt, and that in making smoke we waste a great deal of fuel.
Of course, it depends upon the kind of light whether steam will or will not put it out, but it is certainly true that a fire or a lighted gas-jet or a lamp may be put out by steam. F or this there are at least two reasons. We use the word steam rather loosely, often me~ning by it liquid water in the airthe steam that we can see. But sometimes we mean by it water-vapour. Wherever there is steam, there is watervapour-that is to say, water in the air in the form of an invisible gas. Now, this water is already burnt; it can neither be burnt any more, nor can it sustain the burning of anything else. In so far as the thing which produces the light is supplied with water-vapour in the air instead of oxygen, it is starved and must go out. But the presence of steam means also the presence of liquid water, and liquid water puts a light out because it so quickly swallows up into itself the heat which is near it, and makes the burning thing so cold that it cannot burn. Every man who smokes a pipe knows the great difference there is between smoking moist tobacco and dry tobacco.
What Makes Water Gurgle Whefl it Oomes out of a Bottle?
We know that the air has pressure, and so, if there is an empty space anywhere, the air will press into it. Now, when we pour water out of a bottle which is full, there must be an empty space left behind in the bottle when the liquid comes out,' and from moment to moment, as that empty space tends to be formed in the bottle, the air outside is bound to rush in to take its place. If the bottle has a wide mouth, like a tumbler, then, as we pour the liquid out, air can flow in evenly, and there is no gurgling. But if we take a full ginger-beer bottle, and hold it upside down, then there is a series of fights going on between the liquid which is trying to get out under the pull of gravitation and the air which is trying to push its way past the liquid to fill up the space in the bottle. Sometimes the air pushes back the ginger-beer, and sometimes the ginger-beer pushes back the air. This means that the air is thrown into little disturbances, which we hear as gurgles. We say that water gurgles, but really it is the air that is disturbed by this contest between it and the water, and we call these disturbances" gurgles."
What is Smoke Made of '1
Smoke is the result of imperfect burning. Most of the things from which we get so much smoke-like coal-if they were properly burnt, would form nothing but gases, which we could not see, and which would very soon flyaway and do no harm to anybody. But in order to burn coal properly some trouble and care are required. When we burn coal in an ordinary fire, we do not supply enough air to it. We put the fresh coal on at the top instead of at the bottom, as we should, and so we only partly burn the coal, and small specks of it, unburnt, are carried up in the draught, and make smoke. The chief stuff in smoke is simply coal in $pecks of various sizes. But the trouble is that a great deal of oily stuff comes out of the coal, and covers the specks of it in smoke, so that these stick to things. We all do wrong in this respect in our fires at home, and the time will come when we shall make our fireplaces differently, so that we can burn our coal in a better way. At present the smoke makes black fogs in many cities, and cuts off a great quantity of the daylight by which we live, besides making everything dirty, destroying plants
Why Does a Glow-worm Glow?
A glow-worm is not a worm at all, but is really a kind of beetle seen during the summer months up to the end of August, on warm banks and hedgerows and in woods and pastures. As soon as the evening's dusk begins, this beautiful insect begins to show a most exquisite yellowishgreen light, caused by what are called luminous organs placed over the tail end. The object of this light is not actually certain, but most of the wise men who study living creatures suppose that the female shows the light for the purpose of attracting males, which do not shine in this way. Whether this is the real reason or not we cannot be quite sure, but the glow-worm is only one of many animals which show light by means of what is called phosphorescence.
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