the difficulty. But, for this purpose, we must step into the house.

Here are two common lookingglasses, which, philosophically speaking, are plane mirrors. I place them

in such a manner on the table that they support one another from falling by meeting at the tops. 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 a little, by making them almost parallel to one another; now look into them, and say what you see.

James. There are more half-crowns now than there were before.

Tutor. It is evident, then, that by reflection only, a single object, for I have made use of but one halfcrown, will give you the idea of a vast number.

Charles. If a little contrivance had been used to conceal the method of making the experiment, I should not have believed but that there had been several half-crowns instead of one.

Tutor. Bring me your multiplying glass; look through it at the candle: how many do you see? or rather, how many candles should you suppose there were, did you not know that there was but one on the table?

James. A great many, and a pretty sight it is.

Charles. Let me see; yes, there are: but I can easily count them; there are sixteen.

Tutor. There will be just as many

images of the candle, or any other object at which you look, as there are different surfaces on your glass. For, by the principle of refraction, the image of the candle is seen in as many different places as the glass has surfaces; consequently, if instead of 16 there had been 60, or, if they could have been cut and polished so small, 600, then the single candle would have given you the idea of 60, or 600. What think you now about the stars?

James. Since I have seen that reflection and refraction will each, singly, afford such optical deceptions, I can no longer doubt, but that, if both these causes are combined, as you say they are with respect to the rays of light coming from the fixed stars, a thousand real luminaries may have the power of exciting in my mind the idea of millions.

Tutor. I will mention another experiment, for which you may be prepared against the next clear star-light night. Get a long narrow tube, the longer and narrower the better, provided its weight does not render it unmanageable: examine through it any one of the largest fixed stars; which are called stars of the first magnitude, and you will find that, though the tube takes in as much sky as would contain many such stars, yet that the single one at which you are looking is scarcely visible, by the few rays which come directly from it: this is another proof that the bril liancy of the heavens is much more owing to reflected and refracted light, than to the direct rays flowing from

the stars.

CONVERSATION II.

Of the Fixed Stars.

CHARLES. Another beautiful evening presents itself; shall we take the advantage which it offers of going on with our astronomical lectures?

Tutor. I have no objection, for we do not always enjoy such opportunities as the brightness of the present evening affords.

James. I wish very much to know how to distinguish the stars, and to be able to call them by their proper

names.

Tutor. This you may very soon learn; a few evenings, well improved, will enable you to distinguish all the stars of the first magnitude which are