Читать книгу Nature's Serial Story - Edward Payson Roe - Страница 17

Amy's thoughts naturally reverted before very long to Mrs. Clifford's pets—the flowers—and she asked how they had endured the intense cold of the night.

"They have had a narrow escape," the old lady replied. "If Maggie had not suggested the tub of water last night, I fear we should have lost the greater part of them."

"Yes," said Mrs. Leonard, "I went to the flower-room with fear and trembling this morning, and when I found the water frozen thick I was in despair."

"It was the water freezing that saved the plants," Webb remarked, quietly. "I put water in the root-cellar before I went to bed last night, with like good effect."

"Well, for the life of me," said Maggie, "I can't understand why the plants and roots don't freeze when water does."

"Come, Burt," added her husband, "you are a college-bred man. You explain how the water draws the frost from the plants."

"Oh, bother!" Burt answered, flushing slightly, "I've forgotten. Some principle of latent heat involved, I believe. Ask Webb. If he could live long enough he'd coax from Nature all her secrets. He's the worst Paul Pry into her affairs that I ever knew. So beware, Amy, unless you are more secretive than Nature, which I cannot believe, since you seem so natural."

"I'm afraid your knowledge, Burt, resembles latent heat," laughed

Leonard. "Come, see what you can do, Webb."

"Burt is right," said Webb, good-naturedly; "the principle of latent heat explains it all, and he could refresh his memory in a few moments. The water does not draw the frost from the plants, but before it can freeze it must give out one hundred and forty degrees of latent heat. The flower-room and root-cellar were therefore so much warmer during the night than if the water had not been there. The plants that were nipped probably suffered after the ice became so thick as to check in a great measure the freezing process."

"How can ice stop water from freezing?" Alf asked, in much astonishment.

"By keeping it warm, on the same principle that your bed-clothes kept you warm last night. Heat passes very slowly through ice-that is, it is a poor conductor. With the snow it is the winter wrap of nature, which protects all life beneath it. When our ponds and rivers are once frozen over, the latent heat in the water beneath can escape through the ice but very gradually, and every particle of ice that forms gives out into the water next to it one hundred and forty degrees of heat. Were it not for these facts our ponds would soon become solid. But to return to the tub of water in the flower-room. The water, when placed there, was probably warmer than the air, and so would give out or radiate its heat until a thermometer, placed either in the room or in the water, would mark thirty-two degrees above zero. At this point the water would begin to freeze, but plants or vegetables would not. They would require slightly severer cold to affect them. But as soon as the water begins to freeze it also gradually gives out its latent heat, and before a particle of ice can form it must give out one hundred and forty degrees of heat to the air and water around it. Therefore the freezing process goes on slowly, and both the air and water are kept comparatively warm. After a time, however, the ice becomes so thick over the surface that the freezing goes on more and more slowly, because the latent heat in the unfrozen water cannot readily escape through the ice. It is therefore retained, just as the latent heat in the water of an ice-covered pond is retained."

"It follows, then," said Leonard, "that after the water beneath the ice in the tub began to freeze slowly, the flower-room, in that same degree, began to grow cold."

"Certainly, for only as the water freezes can it give out its latent heat. The thick wooden side of the tub is a poor conductor; the ice that has formed over the surface is even a worse, and so the water within is shielded from the cold. It therefore almost ceases to freeze, and so becomes of no practical use. An intelligent understanding of these principles is of great practical value. If I could have waked up and placed another tub of water in the room at two or three o'clock, or else taken all of the ice out of the first one, the process of freezing and giving out heat would have gone on rapidly again, and none of the plants would have suffered. I have heard people say that putting water in a cellar was all a humbug—that the water froze and the vegetables also. Of course the vegetables froze after the water congealed, or the cellar may have been so defective that both froze at the same time. The latent heat given out by a small amount of freezing water cannot counteract any great severity of frost."

"The more water you have, then, the better?" said his father.

"Yes, for then there is more to freeze, and the effect is more gradual and lasting."

"I feel highly honored, Webb," said his mother, smiling, "that so much science should minister to me and my little collection of plants. I now see that the why and wherefore comes in very usefully. But please tell me why you put the plants that were touched with frost into cold water, and why you will not let the sunlight fall on them?"

"For the same reason that you would put your hand in cold water if frost-bitten. Your expression, 'touched with frost,' shows that there is hope for them. If they were thoroughly frozen you would lose them. Your plants, you know, are composed chiefly of water, which fills innumerable little cells formed by the vegetable tissue. If the water in the cells is chilled beyond a certain point, if it becomes solid ice, it expands and breaks down the tissue of the cells, and the structure of the plant is destroyed. If the frost can be gradually withdrawn so as to leave the cells substantially intact, they can eventually resume their functions, and the plant receive no very great injury."

"But why does sudden heat or sunlight destroy a frosted plant?"

"For the same reason that it breaks down the vegetable tissue. Heat expands, and the greater the heat the more rapid the expansion. When the rays of the sun, which contain a great deal of heat, fall on any part of a frost-bitten plant, that part begins to expand so rapidly and violently that the cellular tissues are ruptured, and life is destroyed. What is more, the heat does not permeate equally and at once the parts affected by frost. The part furthest away from the heat remains contracted, while the parts receiving it expand rapidly and unequally, and this becomes another cause for the breaking up of the vegetable tissue. The same principle is illustrated when we turn up the flame of a lamp suddenly. The glass next to the flame expands so rapidly that the other parts cannot keep pace, and so, as the result of unequal expansion, the chimney goes to pieces. With this principle in mind, we seek to withdraw the frost and to reapply the vivifying heat very gradually and equally to every part, so that the vegetable tissues may be preserved unbroken. This is best done by immersing them in cold water, and then keeping them at a low temperature in a shady place. As the various parts of the plant resume their functions, the light and heat essential to its life and growth can gradually be increased."

"It seems to me that your theory is at fault, Webb," said Leonard. "How is it that some plants are able to endure such violent alternations of heat and cold?"

"We don't have to go far—at least I do not—before coming to the limitations of knowledge. What it is in the structure of a plant like the pansy, for instance, which makes it so much more hardy than others that seem stronger and more vigorous, even the microscope does not reveal. Nature has plenty of secrets that she has not yet told. But of all people in the world those who obtain their livelihood from the soil should seek to learn the wherefore of everything, for such knowledge often doubles the prospect of success."

"Now, Amy," said Burtis, laughing, "you see what sort of a fellow Webb is. You cannot even sneeze without his considering the wherefore back to the remotest cause."

"Are you afraid of me, Amy?" asked Webb.

"No," was the quiet reply.

Amy spent the greater part of the day in unpacking her trunks, and in getting settled in her home-like room. It soon began to take on a familiar air. Hearts, like plants, strike root rapidly when the conditions are favorable. Johnnie was her delighted assistant much of the time, and this Christmas-day was one long thrill of excitement to the child. Her wonder grew and grew, for there was a foreign air about many of Amy's things, and, having been brought from such a long distance, they seemed to belong to another world. The severe cold continued, and only the irrepressible Burtis ventured out to any extent. When Alf's excitement over his presents began to flag, Webb helped him make two box-traps, and the boy concealed them in the copse where the rabbit-tracks were thickest. Only the biting frost kept him, in his intense eagerness, from remaining out to see the result. Webb, however, taught him patience by assuring him that watched traps never caught game.

Beyond the natural home festivities the day passed quietly, and this was also true of the entire holiday season. Cheerfulness, happiness abounded, and there was an unobtrusive effort on the part of every one to surround the orphan girl with a genial, sunny atmosphere. And yet she was ever made to feel that her sorrow was remembered and respected. She saw that Mr. Clifford's mind was often busy with the memory of his friend, that even Burt declined invitations to country merrymakings in the vicinity, and that she was saved the ordeal of meeting gay young neighbors with whom the Clifford home was a favorite resort. In brief, they had received her as a daughter of the house, and in many delicate ways proved that they regarded her as entitled to the same consideration as if she were one. Meanwhile she was shown that her presence cast no gloom over the family life, and she knew and they knew that it would be her father's wish that she should share in all the healing gladness of that life. No true friend who has passed on to the unclouded shore would wish to leave clouds and chilling shadows as a legacy, and they all felt that in Amy's case it had been her father's desire and effort to place her under conditions that would develop her young life happily and therefore healthfully. There is the widest difference in the world between cheerfulness and mirthfulness which arise from happy home life and peaceful hearts, and the levity that is at once unfeeling, inconsiderate, and a sure indication of a coarse-fibred, ill-bred nature. Amy was made to feel this, and she found little indeed which jarred with memories that were only sad, not bitter or essentially depressing. Every day brought new assurance that her father's wishes and hopes in her behalf had been fulfilled to a degree that must have added to his heavenly content, could he have known how well he had provided for her. And so the busy days glided on; and when the evening brought the household together, there were music, reading aloud, and genial family talk, which usually was largely colored by their rural calling. Therefore, on New-Year's morning Amy stood as upon a sunny eminence, and saw her path leading away amid scenes that promised usefulness, happiness, and content.