_Mr Barlow._--Will you then take notice of what you have now been saying? What was first only a little dusky speck became a vessel with one mast, and now this vessel with one mast plainly appears a ship of a very large size, with all her masts and sails, and rigging complete. Yet all these three appearances are only the same object at different distances from your eye. _Tommy._--Yes, sir; that is all very true indeed. _Mr Barlow._--Why, then, if the ship, which is now, full in sight, were to tack about again, and sail away from us as fast as she approached just now what do you think would happen? _Tommy._--It would grow less and less every minute, till it appeared a speck again. _Mr Barlow._--You said, I think, that the sun was a very small body, not bigger than a round table? _Tommy._--Yes, sir. _Mr Barlow._--Supposing, then, the sun were to be removed to a much greater distance than it is now, what would happen? Would it appear the same to your eyes? Tommy considered some time, and then said, "If the ship grows less and less, till at last it appears a mere speck, by going farther and farther, I should think the sun would do the same." _Mr Barlow._--There you are perfectly right; therefore, if the sun were to depart farther and farther from us, at last it would appear no bigger than one of those twinkling stars that you see at so great a distance above your head. _Tommy._--That I perfectly comprehend. _Mr Barlow._--But if, on the contrary, one of those twinkling stars were to approach nearer and nearer to where you stand, what do think would happen? Would it still appear of the same size? _Tommy._--No, sir. The ship, as it came nearer to us, appeared every moment larger, and therefore I think the star must do the same. _Mr Barlow._--Might it not then appear as big as the sun now does, just as the sun would dwindle away to the size of a star, were it to be removed to a still greater distance? _Tommy._--Indeed I think it might. _Mr Barlow._--What, then, do you imagine must happen, could the sun approach a great deal nearer to us? Would its size remain the same? _Tommy._--No; I plainly see that it must appear bigger and bigger the nearer it comes. _Mr Barlow._--If that is the case, it is not so very certain that the earth we inhabit is bigger than the sun and stars. They are at a very great distance from us; therefore, if anybody could go from the earth towards the sun, how do you think the earth would appear to him as he journeyed on? _Tommy._--Really I can hardly tell. _Mr Barlow._--No! Why, is it not the same thing, whether an object goes from you, or you from the object? Is there any difference between the ship sailing away from us, and our walking away from the ship? _Tommy._--No, sir. _Mr Barlow._--Did you not say that if the sun could be removed farther from our eyes, it would appear less? _Tommy._--To be sure it would.