the starry heavens with powerful instruments, have been made in vain. They have, on the contrary, been of incalculable advantage in establishing many important and useful facts, upon which are founded the regulations of the calculation of time; and, more especially, in perfecting the science of navigation. They have opened to our view, in an awe-inspiring manner, the immensity, beauty, and harmony of the works of the Almighty, profusely disseminated in the fearful depths of illimitable space, and thus, by showing man how limited is his sphere of action in this vast creation, assured him of the insignificance and folly of human pride. In a clear frosty night, we think we see with the naked eye an innumerable multitude of stars; but the fact is that we cannot, under the most favorable circumstances, see more than two or three thousand above the horizon at the same time; but we are informed that Dr. Herschel saw 588 stars in the field of his telescope at once, and computed, in a very small portion of the celestial hemisphere 258000 stars. To give the student a clearer idea of the distance of these orbs from each other, let us suppose the earth stationary at the nearest probable distance, and no doubt we might say possible distance, from Sirius, namely 10 millions of millions of miles; that the creation took place 6000 years ago, (the year consisting of 365 days;) and that a cannon ball, shot from Sirius at that time, had continued to move, with its initial velocity of 1200 feet per second, in a direct line towards the earth we find that it would have travelled 43033090909 1 miles, or not quite the two hundred and thirtieth part of the distance; and hence, that it would require, to perform the. whole of its flight, upwards of one million three hundred and eighty thousand years. Let us close this article with the sublime words of the Prophet Isaiah, c. 40, v. 26: "Lift up your eyes on high, and behold who hath created these things, that bringeth out their host by number: he calleth them all by names, by the greatness of his might, for that he is strong in power; not one faileth." 295. The extremities of the earth's axis-which points, with respect to the diurnal revolution, appear stationary-are called the North and South poles. The equator is an imaginary line which passes round the earth and is equally distant from either pole. A line drawn directly over the head of an observer, and pointing north and south, is called a meridian line, or the meridian of the place where he stands. This line, in its extension round the earth, passes through the poles, and cuts the equator at right angles. When a star, in its apparent revolution, passes the meridian of any place, it is said to culminate, and the time which elapses between any two culminations of a fixed star, or one entire revolution of the earth about its axis, is called a sidereal day, from the Latin sidus, a star. 296. From the time that the sun's centre passes the meridian till it returns to the meridian again, is called a solar day. As the sun is not in the centre of the earth's orbit,* the motion of the earth in its orbit is somewhat accelerated by a nearer approach to, and retarded by a recession from that luminary. From this, as well as other causes, the solar day is not of uniform length; it is, however, the medium length of a solar day, or average length of all the solar days in a year, which is the time shown by a well-regulated clock; that is to say, we divide the time of a mean solar day into 24 hours, such as shown by the clock. This is the time in common use, called by astronomers Mean Solar, or Common Time. 60 seconds, sec. make... 60 minutes 24 hours 7 days.... 4 weeks.. 13 months, 1 day, and 6 hours, or 365 days 6 hours....... A labourer's month consists of 26 mercantile month of 30 days. 1 minute, m. .1 hour, h. ..1 day, d. Julian year, y. working days, and a The odd 6 hours of the Julian year are not reckoned till they amount to a day: a common year, therefore, consists of 365 days, and every fourth year, called bissextile or leap-year, of 366. The year is also divided into 12 calendar months, which, in number of days, are irregular, as follows: *Orbit, the figure circums.ribed by the revolution of a planet. When the year is exactly divisible by 4, it is leap-year, in which the second month (February) has 29 days. 297. The solar or tropical year is found, by observation, to consist of 365 d. 5 h. 48 m. 51 sec. Now, as the motion of the earth in its orbit and that on its axis are both in the same direction, it is evident that the earth must perform rather more than one entire revolution on its axis, while the sun, at a mean rate, appears to pass from any meridian to the same meridian again, and that the successive increments* will, in one year, amount to one entire revolution of the earth about its axis; that is, the earth will, in one year, perform one more revolution on its axis than the number of apparent revolutions made by the sun in the same time. The ratio, therefore, of the sidereal day to the solar, being inversely as the number of each which composes the solar year, will be nearly as 365 to 366, or 385, and, therefore, if we multiply 24 hours by 365 and divide by 366, the result will be the length of a sidereal day, in mean solar time, very nearly. Thus: 365 X 24 = 3669 23 h. 56 m. 4 sec. the length of a sidereal day, or the time in which the earth performs one revolution on its axis. If we subtract the length of the sidereal from that of the solar day, we find that the difference is 3 m. 56 sec., or very nearly 4 minutes. Hence, a fixed star will culminate on any day nearly 4 minutes, by the clock, sooner than on the preceeding day. If, therefore, you stretch a meridian line over head, and with a plumb line set a post directly underneath, you may * Increments, portions of increase. fix in the post a piece of tin with a very small hole in it, through which you may observe the culmination of any fixed star. A star of the first magnitude, and having a good elevation, is best; such as Aldebaran in Taurus, Bellatrix in Orion, or any other fixed star, which you can easily recognize. Then, if, by your clock or watch, the star culminates about 4 minutes sooner each night than on the preceding, the clock or watch is well regulated. If, by the clock, the star culminates more than 4 minutes sooner, the clock goes too slow, and the excess of time above 4 minutes is the time the clock has lost. If, on the contrary, the star does not culminate till the same hour as on the preceeding evening, the clock has gained 4 minutes; and if it does not culminate till past the hour by the clock, 4 minutes added to the time past the hour, will show how much the clock has gained. 298. For the exact time of day, observe, through a screen* of some kind, to protect the eye, the time when the sun's centre passes the meridian. This will be the mean solar noon, if the observation is taken on or about the 15th of April, the 15th of June, the 1st of September, or the 24th of December. If the observation is taken between those times, look at the Almanack for the equation of time: then, if the sun is fast of the clock, subtract from the apparent noon; if slow, add to the apparent noon, the equation of time, which will give the true time by the clock. 299. The true solar year not being equal to the year of 365 days 6 hours upon which Julius Cæsar established the leapyear, (the difference, 11 m. 9 sec., amounting, in about 130 years, to a whole day,) Pope Gregory XIII. ordered that every 100th year, which, according to the Julian method, would be bissextile, should be a common year of 365 days, except those centurial years, which, when we cut off two ciphers on the right, are divisible by 4, which were to remain bissextile. This is called the Gregorian method, or new style. 300. If the fixed stars could be seen in the daytime, the sun would, by the earth's daily motion in its orbit, from west to east, appear to progress among them in the same direction. The great circle or path described by the sun among the fixed * Very important. The omission would certainly injure the sight of the observer. stars, in his apparent annual revolution, caused by the real revolution of the earth, is called by astronomers, the ecliptic. A broad circle of the heavens, about 8 degrees on each side of the ecliptic, is called the zodiac, from the Greek zo-on, an animal, because most of the twelve parts into which it was divided by the ancient Chaldeans or Egyptians were named after animals. The following are the divisions of the ecliptic or circle of the zodiac: Astronomical Measure. 60 seconds (") make...... 1 minute, '. 60 minutes.... 30 degrees... 1 degree, °. 1 sign, s. 12 signs, or 360°, the whole circle of the zodiac. Astronomers apply the above measure in calculating the motions and angular distances of the planets and other celestial bodies. 301. A circle is a round figure in a plane, (104,) generated by the revolution of a finite straight line in that plane, about one of its extremities, which remains fixed; and this fixed point is called the centre. The line described by the motion of the other extremity is called the circumference, which is, of course, in all its parts, equally distant from the centre ; and hence all straight lines drawn from the centre to the circumference are equal. These straight lines are called radii of the circle, and any one of them a radius. α If two straight lines cut one another at right angles, (103,) they may be considered as four straight lines which meet in one point, making equal angles with each other. Now, if round the point in which they meet, called the point of intersection, we describe a circle, its circumference will be divided into 4 equal parts, called arcs. Thus, in the circle abde, the angles at the point c, being right angles, are equal to one another, and the arcs ae, ed, db, and ba, upon which they stand, are also equal. b d First, it is evident that a straight line drawn through the centre, from side to side, divides the circle into two equal parts. For, in describing the circle, as the distance from the |