Tommy could hardly find words to express his pleasure and admiration, and he entreated Mr Barlow in the most earnest manner to explain to him the reason of all these wonderful sights. "At present," said Mr Barlow, "you are not sufficiently advanced to comprehend the explanation. However, thus much I will inform you, that both the wonderful tube which showed you the moon so much larger than you ever saw it before, and this curious exhibition of to-night, and a variety of others, which I will hereafter show you, if you desire it, depend entirely upon such a little bit of glass as this." Mr Barlow then put into his hand a small round piece of glass, which resembled the figure of a globe on both sides. "It is by looking through such pieces of glass as this," said he, "and by arranging them in a particular manner, that we are enabled to perform all these wonders." "Well," said Tommy, "I never could have believed, that simply looking through a bit of glass could have made such a difference in the appearance of things." "And yet," said Mr Barlow, "looking at a thing through water alone, is capable of producing the greatest change, as I will immediately prove to you." Mr Barlow then took a small earthen basin, and, putting a half-crown at the bottom, desired Tommy gradually to go back, still looking at the basin, till he could distinguish the piece of money no longer. Tommy accordingly retired, and presently cried out, that, "he had totally lost sight of the money." "Then," said Mr Barlow, "I will enable you to see it, merely by putting water into it." So he gradually poured water into the basin, till, to the new astonishment of Tommy, he found that he could plainly see the half-crown, which was before invisible. Tommy was wonderfully delighted with all these experiments, and declared that from this day forward, he would never rest till he had made himself acquainted with everything curious in every branch of knowledge. "I remember reading a story," said Mr Barlow, "where a telescope (for that is the name of the glass which brings distant objects so much nearer to the eye) was used to a very excellent purpose indeed." "Pray, how was that?" said Tommy.