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. It is generally admitted, and on good authority too, that there are never more than one thousand stars 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 experience of one sense to the aid of another, we are seldom subject to this inconvenience.

Charles. Do you not know, that 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; we had it from papa, a great while ago. But 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, 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 thousand 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 that 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 wondrous 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