Francis J. Grund

“ You have learned, in the preceding lesson, that the Earth and the other Planets are regularly moving round the Sun; but you must know that the time which each requires to complete a whole revolution, that is, the time which each needs to move once round, cannot be the same with all; as you may easily judge yourself: for the Planets which are next to the Sun will, of course, have a much smaller journey to perform, than those which are further from it. ”

“ While the Earth needs a whole year for one revolution round the Sun; Mercury requires but Eightyone days, and Venus only about two thirds of One of our years. Mars, on the contrary, needs for one of his revolutions almost Two years; Vesta almost Four; Juno, Ceres and Pallas over Four years; Jupiter almost Twelve, Saturn over Twentynine, and Herschel nearly Eightyfour of our years! ”

“ You see from this that the revolution of the Earth round the Sun gives us a means of measuring time, by which we are able to bring order and regularity into our business and transactions of life. For the making of clocks and watches is but a late invention, and we should be left entirely in the dark as regards the history of former ages, and a great many people would, at this present moment, be incapable of forming a correct estimate of time, if Providence had not given to all this appropriate means of measuring it. ”

“ When the Moon is in a, then the light of the Sun falls just on that side of it which is turned from the Earth. It is then, we have New Moon. When in b, a small brim of the Moon is seen, because a small portion of its lighted surface is then turned towards the Earth.—When in c half of her lighted surface is turned towards us, and we have the First Quarter. In d a still greater portion of the Moon’s lighted surface is visible, and in e, we have Full Moon, because her whole lighted surface is then turned towards the Earth. ”

“ Most all Stars appear to us, every night in the same position; they seem actually to be fixed in the heavens; and for this reason they are called fixed Stars. There are however Ten others, of which it has been ascertained that they move regularly round the Sun in large circles. These are called Planets or wandering Stars.—The fixed Stars are supposed to be similar to the Sun, in as much as they are bodies which have their own light. The Planets, on the contrary, are of themselves dark bodies, and receive, like our Earth, light and warmth from the Sun. ”

“ For if the Earth would always keep the same relative position to the Sun, then that portion of it, which would then be turned toward the Sun, would have continual day, whilst the other, which would then be turned away from him, would be enveloped in perpetual darkness. But as it is now arranged by the Earth’s rotation on its Axis, most every portion of its surface must at least once every Twentyfour hours be turned toward the Sun and receive from him light and heat. ”

“ What proportion does the extent of America bear to that of Asia? What relation do these continents bear to Europe or Australia? What is the next greatest portion on our globe? Which continent is the smallest? What relation does the surface of the Moon bear to America or Asia?
[§ 34.] Is the whole Earth equally illumined or heated by the Sun? Why not? What is, therefore, the surface of our Earth divided into? Upon what portion of our Earth do the Sun’s rays fall perpendicular? What portion do they strike more obliquely? What people, therefore, will experience the greatest heat? ”

“ During the time that the Earth is performing her journey round the Sun, the Moon, our constant attendant, is continually moving round the Earth, and completes one of these revolutions in little more than Twentyseven days.—Very important and interesting to us are the changes in appearance which she exhibits during each of these revolutions.—You probably will know, that the Moon does not appear to us, at all times, the same. ”

“ The man who is represented as standing on a portion of our Earth, will at first only see the topmast of a vessel at sea; when she comes nearer his eye will discover a much greater portion of her; but when in the third position every part of the vessel will be visible.
§ 5. Some of the Planets are, in their motion round the Sun, accompanied by other dark bodies, which, like the Planets themselves, receive light and heat from the Sun. These are called Satellites or Moons. Such a Satellite is the Moon which accompanies our Earth ”

“ How many has Herschel? By what is Saturn particularly distinguished from all other Planets?
[§ 10.] Are all Planets of the same magnitude as our Earth? Are the Planets in comparison to the Sun large or small bodies?—Is the Sun much larger than any of the Planets? Is the Sun larger or smaller than all the Planets, including our Earth, taken together? Which is the greatest of all Planets? Which Planet ranks, in magnitude, next to Jupiter? Which of the Planets ranks third in magnitude? Which, Fourth? What Planets are smaller than our Earth? What Planets are smaller than the Moon? ”

“ While the Moon is moving round the Earth, it often occurs that she is placed in a direct line between ourselves and the Sun. In this case a greater or less part of the Sun is concealed from us, which causes a diminution of light or a partial darkness on our Earth. ”

“ The double motion of the Planets,—progressive and rotary,—is perhaps one of the most difficult things for young pupils properly to understand, without some popular illustration. If the teacher, therefore, has no orrery to show this motion to his pupils, he may compare it to a screw which is turned round whilst it suffers at the same time a progressive motion; or perhaps with more propriety to a spinning-top, which is continually turning on its Axis, while at the same time it describes large circles. ”

“ RECAPITULATION OF LESSON I.
[If the pupil has learned and understood this lesson, it may perhaps be not unreasonable to suppose he will like to know something more about the Planets and the Moons in our system. But the teacher ought not to allow him to enter upon the second lesson, before he has recapitulated the first.]
QUESTIONS.
[§ 1.] Does the Earth, or the globe on which we live, comprise the whole world which God has created? Is our Earth any considerable portion of the Universe? What other bodies belong to it? Why do the Stars appear to us so small? ”

“ Besides the Planets and Moons there is yet another class of bodies, moving round the Sun in exceedingly long ovals. They are but seldom visible, and are distinguished from other heavenly bodies by a tail which is often three, four, and more times larger than the body itself. ”

“ They move round the Sun in exceedingly long ovals, having their transparent tails always turned away from that luminary. What is most remarkable about them is the astonishing degree of heat to which they are exposed on account of passing so near the Sun, and the astonishing velocity with which they travel. ”

“ I represents the surface of the Earth divided into land and water. Were all land on our Earth put together in a circle, and the water placed round it, then the land would only fill the inner circle, the water occupying the surrounding ring, a space nearly four times as large as the circle. Fig. II, III, IV, V and VI represent the comparative surfaces of America, Europe, Asia, Africa and Australia. ”

“ When viewed through a good telescope she exhibits phases similar to those of the Moon (Lesson III, § 17) , which proves her spherical form (Lesson I, § 3) . The mountains in Venus have been calculated to be at least Six times as high as those on our Earth. Her Atmosphere is only half as dense as ours.
§ 29. Mars appears in many respects similar to our Earth. His light is red and changeable; his surface exhibits black changeable spots (see Figure II, Plate X) . Some philosophers pretend to have noticed a region of ice on his poles. His atmosphere is twice as dense as ours.
No. X. ”

“ The Comet which appeared in the year 1680, is supposed to sustain a heat nearly Two Thousand times greater than that of red hot iron, and to move at the rate of several Hundred Thousand miles an hour!! ”