The Boys' And Girls' Library Part 5

2. The next thing is to cement the tube to the cork. In order to do this, the water is first to be poured into the phial. About one quarter or one fifth as much as the phial will contain, will be sufficient. When this is done, the neck of the phial inside should be wiped dry, for the cork is to be sealed into it, and unless the gla.s.s is dry, the sealing-wax will not adhere. Then the tube is to be pa.s.sed through the cork, and the cork put into its place, and the tube slipped down until the lower end reaches below the surface of the water, and nearly touches the bottom of the phial. Observe, then, at what part of the tube the cork comes, for this part is to be heated, and covered with sealing-wax, in order to seal it into the cork. It may be marked with a touch of ink from a pen, at a point just above where it issues from the cork. Then take out the cork with the tube from the phial, and slip the cork along down towards the lower end of the tube, so that you can put the wax upon the gla.s.s.

In order to cover the part of the tube, which is to pa.s.s through the cork, with sealing-wax, it must be heated; for sealing-wax will not adhere to gla.s.s, or any other smooth or hard substance, if it is cold.

To heat gla.s.s requires some care. It must be heated gradually, and one part must not be made very hot, while the adjoining parts remain cold; for gla.s.s will not bear sudden changes of temperature, or a great difference of temperature in contiguous parts. Therefore, in heating the gla.s.s, you must proceed gradually. Hold the part over the flame of a lamp, but not so as to touch the flame, and move it backward and forward, so as to warm a portion of one or two inches in length, equally. Then you can hold it more steadily, in such a manner as to heat the central portion. As you do this, hold a stick of sealing-wax, so as to touch the hottest part of the gla.s.s with it occasionally, that is, the part immediately below the ink mark. When the gla.s.s is hot enough to melt the sealing-wax, the gla.s.s will coat itself with the wax.

After holding it a moment over the flame, turning it round and round, so as to melt all parts of the wax equally, the cork is to be slipped back again over it into its place, where it will become firmly fixed, as the work cools. Thus the tube will be cemented into the cork.

3. Nothing now remains but to cement the cork into the neck of the phial. The cork ought to be of such a size, that it will go well down into the neck of the phial, so as to have the top of it a little below the upper part of the neck. For the whole of the upper part of the cork ought to be covered with sealing wax, in order to make it air tight, and this can be best done if the gla.s.s rises a little above the top of the cork. If necessary, therefore, the upper part of the cork must be carefully removed with a penknife, and then, when it is properly fitted, the sides may be covered with sealing wax, by heating the wax in the lamp and rubbing it on all around. When it is covered with a thin coat of wax, it should be held over the lamp a moment, turning it round and round, until it is melted in every part; and the neck of the phial should be heated in the same gradual and cautious manner recommended in the case of the tube. When both are of the proper temperature, the cork must be pressed down into its place. Before the wax cools, see that the bottom of the tube does not quite touch the bottom of the phial, and observe also that the tube stands perpendicular. If it does not, it may be gently pressed to one side or the other, as may be required, and held so until the wax has cooled, when it will retain its position. The top of the cork must then be covered with sealing wax, and the surface smoothed by holding it over a lamp until its inequalities run together. Thus the cork will be cemented into the phial, and the air thermometer completed, with the exception of the scale. And the following experiments can be performed with it:--

Exp. 1. On examining the instrument, it will be observed that there is a portion of air closely confined in the upper part of the phial. It cannot escape up the tube, for the water covers the lower end of the tube. If now the instrument is put into a warm place, so as to expand this body of air within the phial, the force of the expansion will press against the water, and cause a portion of it to rise in the tube. When so much water has thus ascended as is necessary to allow such a degree of additional s.p.a.ce within, as will enable the expansive force of the air within exactly to balance the pressure in the top of the tube from without, the water will remain at rest. If now the air is warmed still more, the expansion will cause the water to rise still higher, until the two forces are again in equilibrium.

Exp. 2. When the water has been forced into the tube as high as it will rise under the greatest heat to which it is safe to expose it, it may be carried again into a cool place. The heat which was in the air and the gla.s.s will now pa.s.s off, and the air within will lose some of its expansive force, and will evince a tendency to return to its former dimensions. This will be shown by the subsidence of the water in the tube. Thus by carrying the instrument successively into warm and cold places, the surface of the water in the tube will be found to rise and fall, thus indicating, by the level at which it stands, the temperature of the air around it, at its several places of exposure. A scale for this thermometer may be formed of pasteboard, and fastened to the tube by threads or slits in the pasteboard, or, in any other convenient manner.

Exp. 3. When the instrument is cooled, the water in the tube does not simply fall by its own weight. It is forced down by the pressure of the outward atmosphere. For although the expansive force of the air within is diminished by the cold, there is still force left, far more than sufficient to counteract the weight of the water. So that the water descends, not by its own weight, but by the pressure of the atmosphere without, acting upon the surface of the water in the tube. This may be proved in the following manner. Raise the water in the tube as high as possible, by placing the instrument before the fire, and then stop the upper end of the tube with the thumb, or a little hot sealing-wax. Now, if the thermometer be taken to a cool place, it will be found that the water will not fall. The pressure from above in the tube being taken off the water is kept up by the expansive force which still remains in the air within. When the stopper is removed from the tube, so as to allow the external atmosphere to press upon the water again, it will immediately subside.

Exp. 4. Whatever may have been the temperature of the room where the thermometer was made, the water in the tube will be, when at that temperature, just level with the water in the phial; and of course, when it begins to rise, it will be some little time before it gets up above the neck of the phial. Now as it can be seen better above the neck of the phial than below, it is convenient to have the instrument so adjusted, as to have the surface of the water in the tube always kept above. This can be effected by forcing a little more air into the phial, thus increasing the expansive force within. A few bubbles of air may be blown in with the breath, by applying the mouth to the top of the tube.

This will add to the force within, so that, even when the thermometer is cold, the water will stand in the tube above the neck of the phial, and all the changes that take place will be above that level, where they can be easily seen.

Exp. 5. Place the mouth at the top of the tube, and blow down into it as long and as hard as you can. By this means you will force air in, until the expansive force within is increased so much that you cannot any longer overcome it. Then, before taking the mouth away, stop the upper part of the tube with the thumb. You will now have so great a quant.i.ty of air within, that it will probably have force enough to raise the water higher than the top of the tube. If so, on taking away the thumb the water will spout out at the top, in a jet,--doing no harm, however, except to sprinkle the spectators. After a few such experiments, you will find that the water has spouted itself all out, and you will be sadly puzzled to know how to get more in without taking out the cork.

There is a very easy way, if you only had philosophical knowledge enough to discover it.

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THE RABBIT.

A STORY FOR LITTLE READERS.

"Henry, dear, do come out to walk, this beautiful afternoon. _I_ am going, and do not want to go alone; _please_ come, won't you?"

"Supposing I should say, No; I won't go; what would you do, sister?"

"I should say, well, suit yourself, brother Henry, and I'll try to go alone; but I _do_ wish you would go with me, it is so pleasant to have _some_ one, and I would rather have you than any one else."

"Well, you are a darling, good little girl, and I _will_ go with you."

"Oh, thank you, thank you, dear Henry," said Caroline; and they were soon in the shady lane which extended from their father's house to their uncle's, who was their next neighbour.

Caroline and Henry wandered on, admiring the beautiful things which surrounded them, and now and then stopping to pick a flower. Often Caroline would leave Henry, examining some plant, (for he was quite a botanist,) and walk along without him.

"Come, Henry; let us walk as far as the brook, and then we'll go home."

"Just wait till I see what this curious flower is," said Henry. But Caroline did not mind him, and continued walking slowly along, that he might catch up with her, when he was ready. Presently she stopped; her eyes sparkled, and she almost screamed with delight; for, on the ground before her, was a beautiful white rabbit. She held her breath for fear of frightening it; but though she drew nearer the dear little creature did not seem disposed to run away; and she soon perceived that it had hurt its foot very much, so that it _could_ not walk. Caroline took the rabbit in her arms, and as she was quite near the brook, she thought she would give it some water; so she stepped on the little bridge, but when there, she found that she had no means of getting any, and she called aloud:

"Henry, come quick; I have found a rabbit almost dead; come quick."

Henry was soon at her side. "Let me see," said he; and he bent forward to look at it. "Poor little thing, we will take you home and nurse you till you are well again."

"Don't you think, brother, that it would drink some water?"

"No, no; we had better take it home at once, and _mother_ will tell us what to do." And the two children hastened home with all speed. Their kind mother gave them directions for their new-found pet, and in a week it was quite well, and their parents gave them leave to keep it to play with, after they had learned their lessons, and as long as they were kind towards this curious little creature.

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THE SLEIGH RIDE.

"Oh, I'm afraid! I'm afraid!" William Jones cried, shrinking back, as his father took his hand, in the act of leading him forward to lift him into a beautiful sleigh, that had just drove up to the door, and in which his mother and elder sister were already seated; their feet comfortably wrapped up in a warm buffalo robe.

"Afraid! what are you afraid of?" Mr. Jones asked, in a tone of surprise.

"Oh, I'm afraid the horses will run away--or that the sleigh will break.

Indeed, I'd rather not go."

"Do you not think that your mother, and sister Ellen, and myself, will be in just the danger you fear?"

"Yes."

"And is not my son willing to share that danger with those he loves?"

"But why do you go, father, when there is danger?"

"We do not think that we shall be in any more real danger, while riding with two gentle horses, than we would be if we were sitting in the house, or walking in the street. But come, William; I cannot stand talking to you here; and it is quite necessary that you try to overcome your fears. So jump in, and take your place alongside of sister Ellen."

"But, indeed, I would rather not go, father," William urged, holding back.

Mr. Jones said no more, but took his boy up gently, though firmly, and placed him beside his sister. Then he got in himself,--took hold of the reins,--spoke to his two fine horses, and at once the whole party began to move off; the sleigh bells jingling a merry tune.

Poor little William clung, frightened, to his sister; and it was a good while before he could get over the idea that the very next moment they would all be thrown over and dashed to pieces. After a while, however, he got used to the motion of the sleigh, and seeing that they pa.s.sed on so smoothly, safely, and merrily, the idea of danger gradually faded from his mind; and long before he reached his uncle's house, he was enjoying the ride as much as the rest.

William's cousins were all delighted to see him, and he spent with them one of the happiest days in his life.

And when the time came for Mr. Jones and his family to return, William parted, with a feeling of reluctance, from his happy playmates. As he again stood by the sleigh, and looked at the two stout horses that were harnessed to it, he felt his old fear stealing over his mind. But he was not only now ashamed of that fear, but felt that to indulge in it was not right. So, with his best effort, he restrained it--stepping resolutely into the sleigh.

The last "good-byes" said, Mr. Jones gave the word, and off they went.

When about half of the way home, and at a time when even the lingering remains of William's timidity had pa.s.sed away, two wild young men, half intoxicated, came dashing along in another sleigh, at a most furious rate. Bent on mischief, and thoughtless of the harm they might occasion, they appeared determined to frighten the horses attached to other sleighs, and thereby cause those who were in them to be thrown out into the snow-banks.

It so happened that the sleigh in which were Mr. Jones and his family, were pa.s.sing near a steep declivity, at the time these young men came up to them, and ran their horses so close upon those of Mr. Jones, that he was compelled either to be rolled down the bank, or receive the shock of their sleigh against his own. He chose the latter alternative. As the two vehicles struck each other, that of Mr. Jones was nearly thrown over, and it so happened that Ellen, who was much alarmed, lost her balance, and but for the fact that William, himself dreadfully frightened, seized hold of, and clung to her with all his strength, she would have been thrown down a very steep hill, and, perhaps, have been killed. As it was, however, no one was injured.

"If it hadn't been for me," William said, while they were all talking over the matter, on arriving at home, "Ellen would have been pitched head foremost down that steep bank."

"But if you had staid at home," his father remarked, "it would not have been in your power thus to have saved, perhaps, your sister's life. And now, an't you glad, my son, you were with us?"