This globe, if the horizon be differently set with respect to the solar ray, will exhibit the various phenomena arising from the situation of the horizon with respect to the sun, either in a right, a parallel, or an oblique sphere; or, having set the horizon to any place, you will see by the central solar ray how long the sun is above or below the horizon of that place, and at what point of the compass he rises, his meridian altitude, and many other curious particulars, of which we shall give a few examples. Set the horizon to coincide with the equator, and place the earth in the first point of Libra; then will the globe be in the position of a parallel sphere, and of the inhabitants of the poles at that season of the year, which inhabitants are represented by the pin at the upper, or 90°, part of the quadrant of altitude: the handle being turned round gently, the earth will revolve upon its axis, and the solar ray will coincide with the horizon, without deviating in the least to the north or south; shewing, that on the 21st of March the sun does not appear to rise or set to the terrestrial poles, but passes round through all the points of the compass, the plane of the horizon bisecting the sun's disc. Now place the horizon so that it may coincide with the poles, and the pin, or 90°, representing an inhabitant, be over the equator; the globe in this position is said to be in that of a right sphere; the equator, and all the parallels of latitude are at right angles, or perpendicular to the horizon; by D D turning the handle till the earth has completed a year, or one revolution about the sun, we shall perceive all the solar phenomena as they happen to an inhabitant of the equator; which are, 1. That the sun rises at six and sets at six throughout the year, so that the days and nights there are perpe tually equal. 2. That on the 21st of March and 22d of September, the sun is in the zenith, or exactly over the heads of the inhabitants. 3. That one half of the year, between March and September, the sun is every day full north; and the other half, between September and March, is full south of the equator, his meridian altitude being never less than 66 degrees. If the pin, or 90°, representing an inhabitant be now removed out of the equator, and set upon any place between it and the poles, the horizon will not then pass through either of the poles, nor coincide with the equator, but cut it obliquely, one half being above, the other half below the horizon; the globe in this state is said to be in that of an oblique sphere, of which there are as many varieties, as there are places between the equator and either pole. But one example will be sufficient; for whatever appearance happens to one place, the same, as to kind, happens to every other place, differing only in degree, as the latitudes differ. Bring the pin, therefore, over London, then will the horizon represent the horizon of London, and in one revolution of the earth round the sun, we shall have all the solar appearances through the four seasons, clearly exhibited, as they really are in nature; that is, the earth standing at the first degree of Libra, and the sun then entering into Aries, the meridian turned into the solar ray, and the hour index set to XII, you will then have the globe standing in the same position towards the sun, as our earth does at noon on the 21st of March. If the handle be turned comes to the western round, when the solar ray edge of the horizon, the hour index will point to VI, which shews the time of sun-setting; London then passes into, and continues in darkness, till the hour index having passed over XII hours, comes again to VI, at which time the solar ray gains the eastern edge of the horizon, thereby defining the time of sun-rising; six hours afterwards the meridian again comes to the solar ray, and the hour index points to XII, thereby evidently demonstrating the equality of the day and night, when the sun is in the equinoctial. You may then also observe, that the sun rises due east, and sets due west. Continuing to move the handle, you will find that the solar ray declines from the equator towards the north, and every day at noon rises higher upon the graduations of the meridian than it did before, continually approaching to London, the days at the same time growing longer and longer, and the sun rising and setting more and more towards the north, till the 21st of June, when the earth gets in the first degree of Capricorn, and the sun appears in the tropic of Cancer, rising about 40 min. past III in the morning, and setting about 20 min. past VIII in the evening; and after continuing about seven hours in the nether hemisphere, appears rising in the north east, as before. From the 21st of June to the 22d of September, the sun recedes to the south, and the days gradually decrease to the autumnal equinox, when they again become equal. During the three succeeding months, the sun continues to decline towards the south pole, till the 21st of December, when the sun enters the tropic of Capricorn, rising to the south-east point of the compass about 20 min past VIII in the morning, and setting about 40 min. past III in the evening, at the south-west point upon the horizon: after which, the sun continues in the dark hemisphere for 17 hours, and then appears again in the southeast as before. From this chill solstice the sun returns towards the north, and the days continually increase in length till the vernal equinox, when all things are restored to the same order as at the beginning. Thus all the varieties of the seasons, the time of sun-rising and setting, and at what point of the compass, as also the meridian altitude and declination every day of the year, and duration of twilight, and to what place the sun is at any time vertical, are fully exemplified by this globe and its apparatus. Before we quit the phenomena particularly arising from the motion and position of the earth, let the globe, with the meridian and horizon, be removed, and the ivory ball which fits upon a pin be placed thereon, to represent the earth. As the axis of this globe stands perpendicular to the plane of the ecliptic, you will find that the solar ray continually points to the equator of this little ball, and will never deviate to the north or south; though, by turning the handle, the ball is made to complete a revolution round the sun. This shews, that the earth in this position would have the days and nights equal in every part of the globe, all the year long; there would have been no difference in the climates of the earth; no distinctions of seasons; an eternal summer, or never ceasing winter, would have been our portion; an unvaried sameness, that would have limited inquiry, and satiated curiosity; and that the variety of the seasons is owing to its axis being inclined to the plane of its orbit. An explanation of the causes of the vicissitudes of the seasons, so naturally introduces the following flections of Mr. Cowper, in his Winter's Walk, that I hope they will not be deemed impertinent, either by the tutor or his pupil. What prodigies can power divine perform And renovation of a faded world, See nought to wonder at. Should God again, As once in Gibeon, interrupt the race Of the undeviating and punctual sun, |