Charles. And what is the green line which crosses it?

Tutor. It is called the Equator; this is an imaginary circle belonging to the earth, which you must take for granted, a little longer, is of a globular form. If you can conceive the plane of the terrestrial equator to be produced to the sphere of the fixed stars, it would mark out a circle in the heavens, called the celestial equator or equinoctial, which would cut the ecliptic in two parts.

James. Can we trace the circle of the ecliptic in the heavens?

Tutor. It may be done with tolerable accuracy by two methods; first, by observing several remarkable fixed stars, to which the moon in its course seems to approach. The second method is by observing the places of the planets.

Charles. Is the moon then always in the ecliptic?

Tutor. Not exactly so; but it is always either in the ecliptic, or within five degrees and a third of it on one side or the other. The planets also, by which I mean, Mercury, Venus, Mars, Jupiter, Saturn, and the Herschel, are never more than eight degrees distant from the line of the ecliptic.

James. How can we trace this line, by help of the fixed stars?

Tutor. By comparing the stars in the heavens, with their representatives on the artificial

globe, a practice which may be easily acquired, as you have seen. I will mention to you the names of those stars, and you may first find them on the globe, and then refer to as many of them as are now visible in the heavens. The first is in the Ram's horn called a Arietis, about ten degrees to the north of the ecliptic; the second is the star Aldebaran in the Bull's eye, six degrees south of the ecliptic.

Charles Then if at any time I see these two stars, I know that the ecliptic runs between them, and nearer to Aldebaran, than to that in the Ram's horn.

Tutor. Yes; now carry your eye eastward to a distance somewhat greater from Aldebaran, than that is east of a Arietis, and Arietis, and you will perceive two bright stars at a small distance from one another called Castor and Pollux ; the lower one, and that which is least brilliant, is Pollux, seven degrees on the north side of the ecliptic. Following the same track, you will come to Regulus, or the cor leonis, which I have already observed is exactly in the line of the ecliptic. Beyond this, and only two degrees south of that line, you will find the beautiful star in the virgin's hand, called Spica Virginis. You then arrive at Antares, or the Scorpion's heart, five degrees on the same side of the ecliptic. Afterwards you will find a Aquila, which is situated nearly thirty degrees north of the ecliptic; and farther on is the star Fomahant in the fish's

mouth, about as many degrees south of that line. The ninth and last of these stars is Pegasus, in the wing of the flying-horse, which is north of the ecliptic nearly twenty degrees.

James. Upon what account are these nine stars particularly noticed?

Tutor. They are selected as the most conspicuous stars near the moon's orbit, and are considered as proper stations, from which the moon's distance is calculated for every three hours of time: and hence are constructed those tables in the Nautical Almanac, by means of which navigators, in their most distant voyages, are enabled to estimate, on the trackless ocean, the particular part of the globe on which they

are.

Charles. What do you mean by the Nautical Almanac?

Tutor. It is a kind of National Almanac, intended chiefly for the use of persons traversing the mighty ocean. It was begun in the year 1767, by Dr. Maskelyne, the Astronomer Royal, and is published by anticipation for several years beforehand, for the convenience of ships going out upon long voyages. This work has been found eminently important in the course of the late voyages round the world for making dis

coveries.

VOL. I.-M

CONVERSATION XXV.

Of the Ephemeris.

Charles. Your second method of tracing the ecliptic, was by means of the position of the planets; will you explain that now?

Tutor. I will; and to render you perfectly qualified for observing the stars, I will devote the present conversation to the purpose of explaining the use of White's Ephemeris, a little book which is published annually, and which is a necessary companion to every young astro

nomer.

James. Must we understand all this to study the stars?

Tutor. You must; or some other book of the same kind, if you would proceed on the best and most rational plan. Besides, when you know the use of this book, which you will completely with half an hour's attention, you have nothing more to do in order to find the position of the planets at any day of the year, than to turn to that day in the Ephemeris, and you will instantly be directed to those parts of the heavens in which the different planets are situated. Turn to the second page.

Charles. Here the astronomical characters are explained.

Tutor. The first twelve are the representatives of the signs into which the circle of the ecliptic is divided, called also the twelve signs of the Zodiac.

Every circle connected with this subject is supposed to be divided into 360 parts, called degrees, and since that of the ecliptic is also divided into 12 signs, each sign must contain 30 degrees. Astronomers sub-divide each degree into minutes and seconds, thus if I would express an angle of 25 degrees, 11 minutes, and 45 seconds, I should write 25°.. 11'.. 45". Or, if I would express the situation of the sun for the 1st of January, 1800, I look into the Ephemeris and find it in Capricorn, or 3 10°.. 56'.. 38". James. What do you mean by the Zodiac?

Tutor. It is an imaginary broad circle or belt surrounding the heavens, about sixteen degrees wide; along the middle of which runs the ecliptic. The term Zodiac is derived from a Greek word signifying an animal, because each of the twelve signs formerly represented some animal; that which we now call Libra, being by the ancients reckoned a part of Scorpio.