Part 15 (2/2)
[Illustration: FIG 61--Inclination of the Earth]
In summer, the pole dips toward the Sun, and the rays of the orb of day cover the corresponding heht Six months later this same hemisphere is in winter, and the opposite hemisphere is in its turn presented to the Sun June 21 is the summer solstice for the northern hemisphere, and is at the same time winter for the southern pole Six months later, on December 21, we have winter, while the southern hemisphere is completely exposed to the Sun Between these two epochs, when the radiant orb shi+nes exactly upon the equator, that is on March 21, we have the spring equinox, that delicious flowering season when all nature is enchanting and enchanted; on September 21 we have the autumn equinox, melancholy, but not devoid of charm
The terrestrial sphere has been divided into different zones, hich the different climates are in relation:
1 The tropical zone, which extends 23 27' from one part to the other of the equator This is the hottest region It is limited by the circle of the tropics
2 The temperate zones, which extend from 23 27' to 66 23' of latitude, and where the Sun sets every day
3 The glacial zones, drawn round the poles, at 66 33' latitude, where the Sun remains constantly above or below the horizon for several days, or even several lacial zones are limited by the polar circles
We ht line that is supposed to pass through the center of the globe and come out at two diametrically opposite points called the _poles_ The diurnal rotation of the Earth is effected round this axis
The nareat circle situated between the two poles, at equal distance, which divides the globe into two herees, by other circles that go froitudes_ or62) The distance between the equator and the pole is divided into larger or smaller circles, which have received the narees are reckoned on the one side and the other of the equator, in the direction of the North and South poles, respectively The longitudes are reckoned from some point either to East or West: the latitudes are reckoned North and South, fro froes, but in passing from North to South of any spot, it is the latitude that alters
[Illustration: FIG 62--The divisions of the globe Longitudes and latitudes]
The circles of latitude are smaller in proportion as one approaches the poles The circumference of the world is 40,076,600 meters at the equator At the latitude of Paris (48 50') it is only 26,431,900 round to travel over in order to accomplish its rotation in twenty-four hours than a point nearer the pole
We have already stated that this velocity of rotation is 465 meters per second at the equator At the latitude of Paris it is not itudes, orthe Earth into quarters, like the parts of an orange or a lobe, and measure some 40,000,000 (40,008,032) th of the meter has been determined as, by definition, the ten-millionth part of the quarter of a celestialupon itself, the Earth spins round the Sun, along a vast orbit traced at 149,000,000 kilometers (93,000,000 miles) from the central focus, a sensibly elliptical orbit, as we have already pointed out It is a little nearer the Sun on January 1st than on July 1st, at its perihelion (_peri_, near, _helios_, Sun), than at its aphelion (_apo_, far, _helios_, Sun) The difference = 6,000,000 kiloreater at perihelion than at aphelion
This second motion produces the _year_ It is accomplished in three hundred and sixty-five days, six hours, nine minutes, nine seconds
Such is the complete revolution of our planet round the orb of day It has received the name of sidereal year But this is not hoe calculate the year in practical life The civil year, known also as the tropical year, is not equivalent to the Earth's revolution, because a very slow gyratory motion, called ”the precession of the equinoxes,” the cycle of which occupies 25,765 years, drags the spring equinox back some twenty ly, three hundred and sixty-five days, five hours, forty-eight minutes, forty-six seconds
In order to si fraction of five hours, forty-eight minutes, forty-six seconds (about a quarter day) is added every four years to a bissextile year (leap-year), and thus we have uneven years of three hundred and sixty-five, and three hundred and sixty-six days Every year of which the figure is divisible by four is a leap-year By adding a quarter day to each year, there is a surplus of eleven minutes, fourteen seconds These are subtracted every hundred years by not taking as bissextile those secular years of which the radical is not divisible by four The year 1600 was leap-year: 1700, 1800, and 1900 were not; 2000 will be The agreement between the calendar and nature has thus been fairly perfect, since the establishorian Calendar in 1582
Since the terrestrial orbit measures not less than 930,000,000 kilometers (576,600,000 miles), which h space at 2,544,000 kilometers (1,577,280 miles) a day, or 106,000 kilometers (65,720 miles) an hour, or 29,500 e, a little faster at perihelion, a little slower at aphelion This giddy course, a thousand times more rapid than the speed of an express-train, is effected without co alone enables us to divine the prodigiousin the vast fields of the Infinite, into the calendar, it must be rereat sense in fixing the New Year on January 1 No reeable season could have been selected And further, as the ancient Roman names of the an with March, the ”seventh” hth) is the tenth; November (the ninth) has become the eleventh; and December (the tenth) has taken the place of the twelfth Verily, we are not hard to please!
These ain, are unequal, as every one knows Witness the si and shortthe knobs and hollows of the fist, the for months, the latter to the short: first knob = January; first hollow, February; second knob, March; and so on[12]
[Illustration: FIG 63--To find the long and short months]
Should not the real renewal of the year coincide with the awakening of Nature, with the spring on the terrestrial hereater portion of Humanity, with the date of March 21st? Should not the months be equalized, and their names modified? Why should we not follow the beautiful evolution dictated by the Sun and by thetime yet before its inhabitants will become reasonable
CHAPTER IX
THE MOON