Read Ebook: A José Estevão by Pato Raimundo Ant Nio De Bulh O

Font size: 10 px 15 px 20 px 25 px 30 px 35 px

Background color: BlackWhiteGrayLight GrayDark GrayDim Gray

Text color: BlackWhiteGrayLight GrayDark GrayDim Gray

Apply/Save settings

Ebook has 137 lines and 15581 words, and 3 pages

"But the eclipse!" interrupted my friend, whose attention had evidently begun to wander. "I think the totality of which you spoke must be at hand, for notice how dark the park has become, and the fireflies are so brilliant under the trees."

The total phase of the eclipse was, indeed, beginning, and we stepped out on the lawn before the door to watch it. The moon had now passed entirely within the earth's shadow, but although her light was almost completely obscured as far as its power to illuminate the landscape was concerned, still the face of the moon was dimly visible, as if concealed behind a thick veil. Certain parts of it had a coppery color, producing a very weird effect.

"Dear me!" exclaimed my companion, "I did not think it would look like that! I na?vely supposed that one could not see the eclipsed moon at all, but that she either disappeared or was turned into a kind of black circle in the heavens. And what a strange color she has! Positively it fills me with awe."

"It is very rare," I said, "for the moon to become invisible during an eclipse. That can only occur when the earth is enveloped in clouds."

"Indeed, and what have the clouds to do with it? If the solid body of the earth cannot cast a shadow dense enough to hide the moon, I should not expect things so evanescent as clouds to be more effective."

"It is all owing to the earth's atmosphere," I replied. "If our globe were not surrounded with a shell of air the moon would always be totally invisible when eclipsed. But the atmosphere acts like a lens of glass inclosing the earth; that is to say, it refracts, or bends the rays of sunlight around the edge of the earth on all sides, and throws a portion of them even into the middle of the shadow, at the moon's distance. It is these refracted rays which cause the singular illumination that you perceive on the moon. But when, as occurs only occasionally, all that part of the atmosphere which surrounds the earth along the edge visible from the moon is filled with clouds, the air can no longer transmit the refracted rays, and then, no light being sent into the shadow, a 'dark eclipse,' as astronomers call it, results. An eclipse of the sun is a very different thing. That is caused not by a shadow but by the opaque globe of the moon passing between the earth and the solar orb. When this occurs the sun is completely hidden behind the moon, and only its corona, which projects beyond the moon on all sides, is visible."

"Indeed! I supposed that all eclipses were very much the same thing."

"I do not see why that should be so."

"It is so, for the reason that when the sun is eclipsed, as I have just told you, the solar corona, which cannot be seen at any other time owing to the overpowering brilliance of the solar orb, becomes plainly visible, and by studying the form and other particulars of the corona astronomers are able to draw most important conclusions concerning the constitution of the sun, the mechanism of its radiation, and its effects upon the earth. During an eclipse of the moon, on the other hand, practically nothing new is revealed, and, accordingly, astronomers pay comparatively little attention to such phenomena. Lunar eclipses, however, possess a certain importance, because by predicting the times of their occurrence and then comparing the predictions with the events, something is learned about the motions of the moon. I should add that recently eclipses of the moon have been carefully watched by a few astronomers, notably by Prof. William H. Pickering, because of peculiar effects which seem to be produced at certain points on the moon by the chill which the shadow casts upon her surface. There are also interesting observations to be made concerning the reflection of heat from the moon during an eclipse. But, upon the whole, a lunar eclipse is mainly interesting as a curious spectacle, and as a test of the correctness of astronomical calculations of the motions of the heavenly bodies.

"I may add, however, that eclipses of the moon have been of some use to historians in fixing the dates of important occurrences thousands of years ago. This is possible because astronomers can by calculation ascertain the times of eclipses in the past as well as in the future. Perhaps the most interesting of all instances of this kind is that which relates to the date of the beginning of the Christian era. This has been fixed by means of an eclipse of the moon mentioned by the ancients as having happened the night before the death of Herod, king of the Jews."

"It seems to me," said my friend, "that the faint light on the moon's face is continually changing. It does not appear constantly to have the same tint. While we have been standing here, I have noticed that some parts have grown darker and others lighter, and that the red color on the right has become a little more intense."

"Yes, and that, too, is no doubt caused by the earth's atmosphere. While the eclipse lasts, the earth is rapidly rotating, and consequently new parts of the atmosphere are continually brought to the edge where their refractive effects come into play. If the atmosphere at the edge of the earth is a little more or a little less dense its refraction varies proportionally. Then, changes in the relative clearness or cloudiness of the air are taking place all the time, and these are reflected in the illumination on the moon."

"It seems to me, then, that the earth would present a very remarkable spectacle if we were now on the moon looking at it."

"Surely it would. Seen from the moon the earth appears several times larger than the sun. For the people of the moon, if we imagine them to exist, an eclipse of the sun is now in progress. For them the earth now occupies the same relative position which the moon occupies for us just before it appears in the west as New Moon. They cannot see it except in silhouette as it passes over the sun. More than an hour ago, if they were watching , they suddenly perceived a black round-edged notch in the side of the sun. Instead of being more or less cloudlike and indefinite in outline, like the shadow of the earth on the moon, this notch appeared to them perfectly black and smooth. At a glance, they saw that the body producing it was much larger than the sun. As the sun's disk was gradually hidden behind the earth the shadow of the latter fell over them, until the sun was wholly concealed. Then--and this is true at the present moment--they perceived that the huge disk of the earth was ringed with light, probably of a reddish tinge. This light, as I have already indicated, is that which the atmosphere refracts around the edge of the earth."

"It must be truly a magnificent sight," said my companion.

"Yes, and it is doubtless rendered far more magnificent by the other phenomena which our people at the moon have before their eyes. In consequence of the virtual absence of air there, an observer on the moon would see all the stars, even in full daylight, blazing in a jet black sky. The brilliance of the stars and of the Milky Way would hardly be increased by the hiding of the sun, but probably the long silvery streamers of the solar corona would glow perceptibly brighter when seen projecting out on each side of the enormous disk of the earth."

"But is it true that the moon has no air?"

"Very, very little, and what little she has is probably different in composition from our atmosphere. Some observations seem to indicate that there is a very rare atmosphere on the moon, but to us it would seem a perfect vacuum. We could not breathe there at all."

"How then do those intelligent inhabitants, whom you have pictured for me watching the earth at this moment, manage to survive?"

"But tell me, has the moon always been so airless?"

"But how, and why, do these gases fly away?"

"They do it by virtue of what physicists call their molecular velocity. A gas, of whatever kind, is a mass of molecules which are in continual vibration, moving in all directions among one another with very great velocities. These velocities have been measured, and it has been found that the molecules of nitrogen, one of the components of the air, move at the rate of two miles in a second. The velocity of the molecules of oxygen is a little less; that of the molecules of hydrogen is very great, nearly seven and a half miles in a second! Now, it is also known that the attraction of the earth is sufficient to retain permanently upon its surface all moving particles or molecules which have a velocity less than seven miles in a second, while the attraction of the moon only suffices to retain those whose velocities fall under a mile and a half in a second. So you perceive that all of the gases I have named would soon escape from the moon, even if they were present upon it at the beginning of its history.

"But," interrupted my companion, "I am puzzled to understand how you know so much about the power of the moon to hold things."

"It is really quite simple," I replied. "The attraction of gravitation, which is a property belonging to all known bodies, is measured by the mass, or amount of matter, in a body. It also varies with the distance between the attracting and attracted bodies. We know, by means which I shall not attempt to describe here, the mass both of the earth and of the moon. We also know the size of both of these bodies. They attract objects as if their entire masses were concentrated at their centers. A body of a certain kind and size at the surface of the earth weighs just one pound. If the earth were reduced to half its actual diameter, while retaining the same mass or amount of matter, more closely packed together, the body which now weighs one pound would then weigh four pounds, because it would be twice as near to the center of the earth as before, and the attraction of gravitation varies according to the square of the distance from the center. As the distance diminishes the force increases. The square of two is four, therefore the body would be attracted with four times the force which it experiences at present. Now, the moon is not only much smaller than the earth, but its average density, or the closeness with which the molecules of its rocks are packed together, is less. It results from these facts that the ratio of the entire mass of the moon is to that of the earth as one to eighty-one. Hence the inherent power of the moon to attract bodies is less than one-eightieth as great as the earth's. If the diameter of the moon were the same as that of the earth, a body weighing one pound on the earth would weigh only one eighty-oneth part of a pound on the moon. But the diameter of the moon is less than one quarter as great as that of the earth. It follows that bodies on the moon are almost four times nearer to the center of attraction. This fact must be taken into account in calculating the force of gravity on the moon's surface. As far as the mass of the moon is concerned, bodies on her surface experience less than one-eightieth of the attractive force which the earth exercises upon bodies on its surface, but this is so far counterbalanced by their greater nearness to the center, that the actual attraction upon them is about one sixth of that which they would experience on the earth."

"Thank you," said my companion dryly, "your explanation appears to me to be very scientific."

"Not by any means as scientific as it might be, or as it ought to be," I replied, laughing. "But, really, if you wish to understand these things you should not be too much afraid of the bugbear 'science.' Science makes the world go nowadays, and everybody ought to know a little about it, just as everybody with any pretensions to education a hundred years ago had to learn more or less Greek and Latin. But let me continue a little farther. Since the force of attraction on the moon is only one sixth as great as it is on the earth, the weight of all bodies is in the same proportion. Pardon me if I guess at your weight; it is, perhaps, 120 pounds. Very well, translated to the moon you would weigh only 20 pounds."

"Dear me, then skipping the rope may be the favorite pastime of middle-aged ladies on the moon."

"And throwing somersaults that of gray-haired lunar gentlemen. Let me tell you of one very interesting consequence of the small force of the moon's gravity, which affects not merely the weight of bodies but the flight of projectiles, and, indeed, all motions of every kind. You will see, when we come to the photographs, that some of the lunar volcanoes are of a magnitude almost incredible. This is doubtless due to the fact that the ejections from volcanic craters there were able, with no greater expenditure of explosive force, to attain an elevation six times that which they would attain if thrown from a volcano on the earth. During the eruption of Vesuvius in April, 1906, the column of smoke, steam, and cinders from its crater reached, according to the measures of Professor Matteucci, a maximum height of about eight miles. On the moon the same force would have blown these things almost fifty miles high! It is not difficult, in view of such facts, to see how the giant volcanic craters and mountain rings of the moon were formed."

In the meantime the eclipse continued, and, having tired of watching it, we returned to the drawing-room.

"When shall we see these famous photographs and begin our imaginary journey in the moon?" my companion asked.

"To-morrow," I replied. "But I shall have to demand one more brief exercise of your patience this evening, while I finish with this subject of eclipses."

"Then we are not through yet?"

"Not quite, for I have not yet told you why the moon is not eclipsed every time she approaches the earth's shadow, and why she does not eclipse the sun once every month at the time of New Moon."

"Well, tell me then, and I promise to be as interested as possible; only please don't talk any more mathematics than is absolutely necessary."

"I think I understand the reason sufficiently. But what a complicated affair you astronomers make of what, it seems to me, should really be a very simple thing."

"It is like a sewing machine," I replied, "which seems very simple when you see it running smoothly, and do not trouble yourself about all the various parts of its mechanism. But if you undertake to explain to yourself, or to make clear to another person, exactly how the machine works, you find that your attention is rather severely taxed, and that the apparent simplicity is based upon no little complexity of construction and interaction of parts. You will have understood from what I have said, that the reason why the moon does not eclipse the sun once every month is based upon the same fact, namely, the inclination of the moon's orbit to the plane of the orbit of the earth; and that when she does eclipse the sun her nodes must be somewhere near a line drawn from the earth to the sun. There is one broad difference between an eclipse of the moon and an eclipse of the sun which I have not yet mentioned. This arises from the fact that the moon being so much smaller than the earth, her shadow, when she hides the sun, does not cover the entire earth, as the earth's shadow covers the whole moon, but comes almost to a point before reaching the earth. The average length of the moon's shadow is only 232,150 miles, 6,690 miles less than the average distance between the moon and the earth. But since, in consequence of the eccentricity of her orbit, the moon's distance is continually varying, the length of her shadow also varies to the extent of about 4,000 miles each way. Thus it may be as short as 228,300 miles, or as long as 236,050 miles. When the greatest length of the moon's shadow coincides with her least distance from the earth , her shadow extends more than 18,000 miles beyond the earth. Under such circumstances its diameter at the surface of the earth is about 167 miles. That is the greatest diameter that the shadow of the moon can have at its intersection with the earth. Ordinarily, when it reaches the earth at all, its diameter is less than 100 miles, and often very much less. If the earth and the moon were motionless during an eclipse, her shadow would form a round, dark spot on the earth, and all observers within the circumference of that spot would behold the sun totally eclipsed. But, in consequence both of the motion of the moon in her orbit, and the rotation of the earth on its axis, the shadow spot moves swiftly in an easterly direction over the earth's surface, forming what is called the path of the eclipse. The astronomer calculates beforehand across what parts of the earth the path will lie, and selects his points of observation accordingly.

"When the length of the shadow is too small to reach the earth, the moon appears projected against the sun as a round black disk, hiding the center of the solar orb, but leaving a brilliant ring all around. Such phenomena are called annular eclipses. There are about three annular eclipses for every two total ones. When the moon, as often occurs, does not traverse the center of the sun's disk, as seen from any part of the earth, a partial eclipse is the result. This means that only a portion of the sun is hidden by the moon. Even a total eclipse appears as a partial one to observers who are not placed within the limits of the shadow path."

"But it seems to me," said my friend, "you have hedged round your eclipses with so many difficulties, what with the tip of the moon's orbit, and what with the shortness of her shadow, that they must be very few in number. Yet I often hear of an eclipse, although I have never seen one before to-night."

This was indeed the case. Going to the door, we saw the earth's shadow slowly withdrawing from the face of the moon, while the landscape was brightening under her returning rays. For a few minutes we watched, in silence, the brilliant spectacle. Then my companion turned to me.

"Would you know my whole thought?" she asked. "I fear that I cannot recall many of the scientific facts you have just been telling me, but for them I can go back, at need, to the books. Yet one thing I feel that I have certainly gained. It is a sense of friendly, companionable interest in the moon. Henceforth she will be more to me than she ever was before. I shall always be conscious, when looking at her face, that she is the offspring of the earth, and that there exists between these two bodies an intimacy that I had never imagined possible. For me your tides and your eclipses seem an inarticulate language, a caressing exchange of communications between these two celestial beings of one blood. To my mind they are, in a certain sense, personalities, and, as a creature of the earth, I feel now my relationship to the moon."

"Very good," I replied. "All science and all forms of knowledge are rooted in the imagination. To-morrow we shall begin with the photographs, and many most interesting things that I have not yet mentioned will then naturally present themselves before us."

"Good night then," said my companion, "and to-morrow I shall count upon the delights of a photographic journey in the moon."

NEW MOON TO FIRST QUARTER

NEW MOON TO FIRST QUARTER

AT breakfast the next morning I asked my friend if she still had sufficient curiosity concerning the moon to induce her to undertake the contemplated journey amid lunar scenes.

"Yes, surely," she replied. "My dreams last night were filled with wonderful spectacles; great cones of shadow flitted continually through the heavens, eclipsing, in turn, moon, sun, and stars; and I stared, as it seemed, for hours at strange faces veiled behind a maze of mathematical diagrams covering the moon. I am not sure that your discourses have made me scientifically much wiser, but I feel that my imagination is sufficiently aroused to enable me to enjoy the photographic excursion that you have proposed, and I am quite ready to start at once."

"Excellent!" I said, producing my portfolio. "Here then are the photographs which I trust will enable us, in imagination, to spend an interesting month upon the moon. These photographs were made at the Yerkes observatory and they represent the moon, as you will perceive, in all of her principal phases, beginning with the narrow crescent of the New Moon, and ending with the similar, but reversed, sickle of the Old Moon."

"Let us take them out into the park under the trees," my friend suggested.

The shafts of morning sunshine, falling through the branches and illuminating the broad lawns and brilliant flower-beds, offered the greatest possible contrast with the strange scenes of the preceding night. We chose the shadow of a huge elm, and had a table placed there for our accommodation. On this I spread the photographs, and my companion began to examine them with many expressions of interest.

Share on: WhatsApp @Hash Facebook Tweet