MANY readers of ST. NICHOLAS have spent hours over those delicately colored wonders, the soap-bubbles. Most of us have wondered how to explain their beauty and form; or, while idly blowing these balloons, we have connected them with some fairy fancy, and have been led to think of charms and enchantments. Many of us believe still, as we believed when children, that no gem surpasses a soap-bubble in beauty; and one cannot help feeling really sorry when each exquisite plaything bursts.

Nor do children alone mourn over their short existence. Sir Isaac Newton, who sought out the secret that a falling apple hinted, said of the soap-bubble that a man or child who could blow one that would last would confer a great benefit upon mankind. You will wonder at this saying, but the truth of it will soon be apparent.

No one yet has been able to make a soap-bubble that will not burst, but by care we can make one that lasts for some time. Its length of life will depend largely upon the mixture used in blowing it, and the care we take in protecting it from drafts. Perhaps some of you do not know how to make a good soap-bubble mixture, so I will give you directions for preparing

one.

Put into a pint-bottle two ounces of best white Castile soap, cut into thin shavings, and fill the bottle with cold water which has been first boiled and then left to cool. Shake well together, and allow the bottle to stand until the upper part of the solution is clear. Decant now of this clear solution two parts, and add one part of glycerin, and you will have a soap-bubble mixture very much like one suggested by Professor J. P. Cook of Harvard College.

Some of you may wonder why bubbles cannot be blown from water alone. It is because the particles do not possess sufficient attraction

for one another to form a film. Mysteriously, the soap increases this attraction, even if the quantity be as small as one-hundredth part of the solution. We add the glycerin to make the film more gorgeous by bringing about a greater play of colors. Bear in mind that a carefully prepared mixture will save you much disappointment.

The solution now being at hand, we use the ordinary clay tobacco-pipe in blowing. Always use a new one, for one in which tobacco has been smoked is poisoned. With a little practice, and a moderate amount of patience, bubbles measuring eight or ten inches in diameter may be produced, and even larger ones if the lungs be refilled. The pipe, of course, should be held steadily, and the breath forced into the bubble evenly. In order to watch a bubble carefully, we may wish to support it in some way. A common table-goblet will make a good stand if its edge is first dipped into melted paraffin, or well soaped, which prevents it from cutting into the film.

Now as to the soap-bubble being a sphere. We find that all bubbles and drops are round. All liquids, when free to act, tend to take on the spherical form. So it is with milk when it falls upon a buttered plate, a rain-drop when it descends, or the dew that glistens so beautifully in the morning sun. In each case the drop is composed of tiny particles that are equally attracted by a central particle, and as they cling regularly around it give the drop a round shape. Your school-books have told you that this attraction that causes all things to try to come together is gravitation. Here is a pretty little stanza written by Samuel Rogers, teaching this truth:

That very law which molds a tear,
And bids it trickle from its source,
That law preserves the earth a sphere

And guides the planets in their course.

In the case of the soap-bubble the case is reversed. The particles of air within press with equal force outward upon the film in all directions, producing the curved surface and making a hollow sphere. If the room is free from drafts, the bubble will be a perfect one, and will teach us the principles that underlie the making of a sphere. This perfect form, however, is seen only when the bubble floats. When resting upon the goblet, it appears very much like an orange. - that is, an oblate spheroid, the true shape of the earth. Putting it into the simplest language, the form of a bubble is due to the holding together of the soap solution, to the outward pushing of the air within and the resistance of the film.

If the air in the room is moderately cool, the bubble will float like a tiny balloon. The mouth and lungs at all times having a temperature of nearly one hundred degrees, the air blown into the toy bubbles is warmer, and consequently lighter than the air which surrounds them; therefore they float, and it is their lightness and grace that, with their beauty, give them such a charm. As soon as the air within the bubble cools, it slowly sinks till it reaches the floor, and the jar of its contact usually ruptures the film.

The extreme thinness of the bubble is indeed wonderful. It is estimated that the film in some places is only one three-millionths of an inch in thickness. Probably few of us can conceive of such thinness. Let me express it in another way. The Old and the New Testament contain some three millions of letters. Now one three-millionth is such a part of an inch as the first letter of the Bible is a part of the sum of all of its letters.

The bubble, however, is not of equal thickness at all points, and it is for this reason that it has the various colors. For instance, wherever the film is orange-red it measures about three onemillionths of an inch; where it is blue, eighty one-millionths of an inch; and at a point where lemon-yellow is prominent, about twenty onemillionths of an inch. Perhaps you wonder why the colors change from one part of the soap

bubble to another. This is because the film of the soap-bubble evaporates and grows thinner, but unequally so at different portions. A greenish blue with a pale rose-red spot near it indicates an extreme thinness, and at such a point the film is ready to give way at the least jar.

You will be glad to know the source of the beautiful colors. Every one is delighted with them, even if not interested by the explanation of their origin. We may say that they come from the light. Light gives color to all objects, but not exactly as it does to the soapbubble. White light from the sun can be broken into the seven colors which we have seen in the rainbow. In that instance the raindrops separate it into its parts. A glass prism will do the same, as you may prove by looking through a glass pendant from a hanging lamp. When the light reaches the surface of the soap-bubble a part is reflected from it, and we see images on its surface as if it were a curved mirror. Another portion of the light, however, enters the film and is separated so that a part of the seven colors are thrown into the bubble, and we can see them at various portions of the opposite surface. Another part of the light, after being broken by the film, is reflected by its inner surface back to our eyes, so that we see colors at the point where the light enters.

After you have observed these things to which I have referred, you may learn very many more by consulting a work on physics and studying light and the laws that govern it. If you care to, you can study the composition of water, soap, and air by reading of these substances in some work on chemistry. Such a simple line of investigation as the study of a mere soap-bubble has often awakened the natural liking for some particular group of studies, and thereby started a boy or girl properly upon a life work.

It is our supposed familiarity with common things that frequently robs them of the study and interest that might otherwise be profitably bestowed upon them.

THERE is a garden on a hill-slope between the snows of the Sierra Nevada and the warm, rich valleys of the coast. It is in that region of Northern California where the pine-belt and the fruit-belt interlace. Both pine and fruit trees grow in that mountain garden, and there, in the new moon of February, six young Almond trees burst into flower.

The Peach and Plum trees in the upper garden felt a glow of sympathy with their forward sisters of the south, but the matronly Cherry trees shook their heads at such an untimely show of blossoms. They foresaw the trouble

to come.

"The Almond trees," they said, "will lose their fruit-buds this year, as they did last and the year before. Poor things, they are so emotional! The first whisper of spring that wanders up the foot-hills sets them all aflame; out they rush, with their hearts upon their sleeves, for the frosts to peck at. But what can one do? If you try to reason with them, 'Our parents and grandparents always bloomed in

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February,' they will tell you, and they did not lose their fruit-buds.'"

"The Almond trees come of very ancient stock," said the Normandy Pear, who herself bore one of the oldest names in France. "Inherited tendencies are strong in people of good blood. One of their ancestors, I have heard, was born in a queen's garden in Persia, a thousand years ago; and beautiful women, whose faces the sun never shone upon, wore its blossoms in their hair. And, as you probably know, their forefathers are spoken of in the Bible."

"A number of persons, my dear, are spoken of in the Bible who were no better than they should be," said the eldest Apple tree. "We

6

go back to the Mayflower'; that is far enough for us; and none of our family ever dreamed of putting on white and pink in February. It would be flying in the face of Providence."

"White and pink are for Easter," said the Pear tree, whose grandparents were raised in a

The Apple tree straightened herself stiffly. "We do not keep the church fasts and feasts," she said; "but every one knows that faith without works is dead. What are these vain blossoms that we put forth for a few days in the spring, without the harvest that comes after ? "

"Now the Apple tree is going to preach," said the light-hearted Peach tree, stepping on the Plum tree's toes. "If we must have preaching, I had rather listen to the Pines. They, at least, have good voices."

"Those misguided Almonds are putting out all their strength in fleshly flowers," the Apple tree continued; "but how, when the gardener comes to look for his crop? We all know, as the Cherry trees said, what happened last year and the year before. It cannot be expected that the Master of the Garden will have patience with them forever."

"The Master of the Garden!" Four young Fig trees who stood apart and listened in sorrowful silence to this talk of blossoms, repeated the words with fear and trembling.

"How long-how much longer," they asked themselves," will he have patience with us?" It was now the third spring since they had been planted, but not one of the four sisters had yet produced a single flower. With deep, shy desire they longed to know what the flower of the fig might be like. They were all of one age, and they had no parent tree to tell them. They knew nothing of their own nature or race or history. Two seasons in succession, a strange, distressful change had come upon them. They had felt the spring thrills, and the sap mounting in their veins; but instead of breaking out into pink and white flowers, like the happy trees around them, ugly little hard green knobs had crept out of their tender bark, and these had swollen and increased in size till they were bowed with the burden of their deformity. Fruit this could not be, for they had seen that fruit comes from a flower, and no sign of a blossom or a bud had ever been vouchsafed them. When inquisitive hands came groping and feeling of the purple excrescences upon their limbs, they covered them up in shame, and tried to

time they were mercifully eased of this affliction; but then the frosts came, and the winter's dull suspense, and then another spring's awakening to hope and fear.

Perhaps we were not old enough before," they whispered encouragement to one another. "Blossoms no doubt are a great responsibility. Had we had them earlier, we might have been foolish and brought ourselves to blame, like the Almond trees. Let us not be impatient; the sun is warm, but the nights are cold. Do not despair, dear sisters; we may have flowers yet. And when they do come, no doubt they will be fair enough to reward us for our long waiting."

They passed the word on softly, even to the littlest Fig tree sister that stood in rocky ground close to the wall that shut the garden in from the pine-wood at its back. The Pines were always chanting and singing anthems in the wood; but though the sound was beautiful, it oppressed the little Fig tree, and filled her with. melancholy. Moreover, it was very dry in the ground where she stood, and a Fig tree must. have drink.

"Sisters, I am very thirsty," she cried. "Have you a little a very little water that you could spare ?"

The sister Fig trees had not much of anything to spare; they were spreading and growing fast, and their own soil was coarse and stony. The water that had so delicious a sound in coming seemed to leak away before their eager rootlets had more than tasted it; still they would have shared what they had, could they have passed it to their weaker sister. But the water would not go uphill; it ran away down, instead, and the Peach and Plum and Pear trees grew fat with what the Fig trees lacked.

"Courage, little sister!" they called to the fainting young tree by the wall. "The morning sun is strong, but soon the shadow of the wood will reach us. Cover thy face and keep a good heart. When our turn shall come, it will be thy turn too; one of us will not bloom without the others."

It was only February, and the Almond trees stood alone, without a rival in their beauty.