you will easily distinguish the others, which are less conspicuous.

Charles. But they have not all names; how are they specified ?

Tutor. If you look on the globe, you will observe that they are dis tinguished by the different letters of the Greek alphabet; and in those constellations, in which there are stars of different apparent magnitudes, the largest is alpha, the next in size ẞ beta, the third y gamma, the fourth delta, and so on.

James. Is there any particular reason for this?

Tutor. The adoption of the characters of the Greek alphabet, rather than any other, was perfectly arbitrary; it is, however, of great importance, that the same characters should be used in general by astronomers of all countries, for by this

means the science is in possession of a sort of universal language.

Charles. Will you explain how this is?

: Tutor. Suppose an astronomer in North America, Asia, or any other part of the earth, observe a comet in that part of the heavens where the constellation of the Plough is situated, and he wishes to describe it to his friend in Great Britain, in order that he may know, whether it was seen by the inhabitants of this island. For this purpose he has only to mention the time when he discovered it; its position, as nearest to some one of the stars, calling it by the Greek letter by which it is designated; and the course which it took from one star towards another. Thus he might say, that on such a time he saw a comet

near in the Great Bear, and that its course was directed from to ß, or any other, as it happens.

Charles. Then if his friend here had seen a comet at the same time, he would, by this means, know whether it was the same or a different comet ?

Tutor. Certainly, and hence you perceive of what importance it is, that astronomers in different countries should agree to mark the same stars and systems of stars by the same characters. But to return to that star, to which you just called my attention, the Cor Leonis; it is not only a remarkable star, but its position is also remarkable; it is situated in the ecliptic.

James.

What is that, sir?

Tutor. The ecliptic is an imaginary great circle in the heavens,

which the sun appears to describe in the course of a year. If you look on the celestial globe, you will see it marked with a red line, perhaps an emblem of the fierce heat communicated to us by that body.

James. But the sun seems to have a circular motion in the heavens every day?

it

appears

A

Tutor. It does; and this is called its apparent diurnal, or daily motion, which is very different from the path to traverse in the course of a year. The former is observed by the most inattentive spectator, who cannot but know, that the sun is seen every morning in the east, at noon in the south, and in the evening in the west; but the knowledge of the latter must be the result of patient, observation.

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 equa tor or equinoctial, which would cut the ecliptic in two parts; and one of these would make an angle with the other of about 23 degrees.

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