CONVERSATION XXII.

OF THE FIXED STARS

TUTOR-CHARLES-JAMES.

CHARLES. The delay occasioned by our unusually long walk, has afforded us one of the most brilliant views of the heavens that I ever

saw.

James. It is uncommonly clear, and the longer I keep my eyes fixed upwards, the more stars seem to appear: how is it possible to number these stars? and yet I have heard that they are numbered, and even arranged in catalogues according to their apparent magnitudes. Pray, sir, explain to us how this business was performed.

Tutor. This I will do, with great pleasure, some time hence, but at present, I must tell you that in viewing the heavens with the naked eye, we are very much deceived as to the supposed number of stars that are at any time visible. is generally admitted, and on good authority too, that there are never more than one thousand stars

It

visible to the sight, unassisted by glasses, at any one time, and in one place.

James. What! can I see no more than a thousand stars if I look all around the heavens? I should suppose there were millions.

Tutor. This number is certainly the limit of what you can at present behold; and that which leads you, and persons in general, to conjecture that the number is so much larger, is owing to an optical deception.

James. Are we frequently liable to be deceived by our senses?

Tutor. We are, if we depend on them singly; but where we have an opportunity of calling in the assistance of one sense to the aid of another, we are seldom subject to this inconvenience.

Charles. Do you not know if you place a small marble in the palm of the left hand, and then cross the second finger of the right hand over the first, and in that position, with your eyes shut, move the marble with those parts of the two fingers at once, which are not accustomed to come into contact with any object at the same time, that the one marble will appear to the touch as two? In this instance, without the assistance of our eyes, we should be deceived by the sense of feeling.

Tutor. This is to the point, and shows that the judgment formed by means of a single sense is not always to be depended upon.

James. I recollect the experiment very well,

But

we had it from papa, a great while ago. that has nothing to do with the false judgment which we are said to form about the number of stars.

Tutor. You are right; it does not immediately concern the subject before us, but it may be useful as affording a lesson of modesty, by instructing us that we ought not to close our minds against new evidence that may be offered upon any topic, notwithstanding the opinions we may have already formed. You say, that you see millions of stars, whereas the ablest astronomers assert, that with the naked eye you cannot at one time see so many as a thousand.

Charles. I should indeed have thought with my brother, had you not asserted the contrary; and I am anxious to know how the deception happens, for I am sure there must be a great deception somewhere, if I do not at this time behold very many thousands of stars in the heavens.

Tutor. You know that we see objects only by means of the rays of light which proceed from them in every direction. And you must for the present, give me credit when I tell you that the distance of the fixed stars from us is immensely great, consequently the rays of light have to travel this distance, in the course of which, especially in their passage through our atmosphere, they are subject to numberless reflections,

and refractions. By means of these, other rays of light come to the eye, every one of which, perhaps, impresses upon the mind the idea of so many separate stars. Hence arises that optical fallacy by which we are led to believe the stars which we behold are innumerable.

James. I should like to see an experiment to confirm this.

Tutor. I have no objection: in every case you ought to require the best evidence that the subject will admit of:

To ask or search I blame thee not, for heaven
Is as the book of God before thee set,
Wherein to read his wond'rous works, and learn
His seasons, hours, or days, or months, or years.

MILTON.

I will show you two experiments which will go a good way to remove the difficulty. But, for this purpose, we must step into the house.

Here are two common looking-glasses, which, philosophically speaking, are plain mirrors. I place them in such a manner on the table that they support one another from falling by meeting at the top. I now place this half-crown between them, on a book, to raise it a little above the table. Tell me how many pieces of money. you would suppose there were, if you did not know that I had used but one.

James. There are several in the glasses.

Tutor. I will alter the position of the glasses