I wonder if I can explain it to an unlearned world, which has not studied the book with gray sides and a green cambric back. Let us try. You know then, dear world, that when you look at the North Star, it always appears to you at just the same height above the horizon or what is between you and the horizon: say the Dwight School-house, or the houses in Concord Street; or to me, just now, North College. You know also that, if you were to travel to the North Pole, the North Star would be just over your head. And, if you were to travel to the equator, it would be just on your horizon, if you could see it at all through the red, dusty, hazy mist in the north, as you could not. If you were just half-way between pole and equator, on the line between us and Canada, the North Star would be half-way up, or 45@ from the horizon. So you would know there that you were 45@ from the equator. Then in Boston, you would find it was 42@ 20' from the horizon. So you know there that you are 42@ 20' from the equator. At Seattle again you would find it was 47@ 40' high, so our friends at Seattle know that they are at 47@ 40' from the equator. The latitude of a place, in other words, is found very easily by any observation which shows how high the North Star is; if you do not want to measure the North Star, you may take any star when it is just to north of you, and measure its height; wait twelve hours, and if you can find it, measure its height again. Split the difference, and that is the altitude of the pole, or the latitude of you, the observer. "Of course we know this," says the graduating world. "Do you suppose that is what we borrow your book for, to have you spell out your miserable elementary astronomy?" At which rebuff I should shrink distressed, but that a chorus of voices an octave higher comes up with, "Dear Mr. Ingham, we are ever so much obliged to you; we did not know it at all before, and you make it perfectly clear." Thank you, my dear, and you, and you. We will not care what the others say. If you do understand it, or do know it, it is more than Mr. Charles Reade knew, or he would not have made his two lovers on the island guess at their latitude, as they did. If they had either of them been educated at a respectable academy for the Middle Classes, they would have fared better. Now about the longitude.