What must I do, then, to make my London pendulum beat seconds on the equator? Why, shorten it a little bit. Yes; or, what is the same thing, move up the weight at the end of the pendulum a little. I must shorten it one-tenth of an inch, or else it will lose sixteen hours in the year. Then all the clocks carried to Melbourne from London will be wrong. Will they go too fast or too slowly in Victoria? They will be a little too slow, as Melbourne is nearer the equator than London is. If a Melbourne clock-maker want his second pendulum to beat seconds in London what directions must he give? He must tell the folks in London to lengthen the pendulum a bit. You will see that by the world being flattened at the poles the degrees of latitude will differ. One close to the equator measures 68-3/4 miles, in Victoria about 69 miles, in England 69-1/8, while in Lapland it would be 69-1/4. What would be the mean length of a degree? About 69-1/20 miles. Let me multiply that by 360, to find the mean circumference of the world; I have it--24,858 miles.” ANNUAL MOTION. The ship was much delayed in the Region of the Calms, as it is called; that is, near the equator. After a while the astronomical dialogue was resumed. “Well, James, look now at your twinkling friends, and tell where you are. I suppose by the North Polar star resting upon the waters to the north, that we must be now nearly on the top of the hill, by the equator. We are so, my lad. But what time did the sun rise this morning? At six, and it set at exactly six this evening. Do you know what day of the month it is? The twenty-third of September. Have you ever observed the sun to rise and set at six o’clock before, on the voyage? No, father. Well, then, you will recollect hereafter that you were upon the equator on the twenty-third of September, when there was equal day and night. But did you not know of equal day and night at home? Yes; about half-way between winter and summer. Just so; that is, at the end of September. Why should it be so there in England and here too? We will try and find out. I think I have pointed out to you the Pleiades. I know them well. They are in the Bull cluster. There happens to be a band of twelve constellations forming a broad circle of the heavens. Is that what is called the Signs of the Zodiac? The same. Can you repeat them? Yes, father. Aries the Ram, Taurus the Bull, Gemini the Twins, Cancer the Crab, Leo the Lion, Virgo the Virgin, Libra the Scales, Scorpio the Scorpion, Sagittarius the Archer, Capricornus the Goat, Aquarius the Water-bearer, Pisces the Fishes. Over there to the eastward is one of these that rose as the sun was setting. The sun is seen opposite one or other of the twelve constellations in each month of the year. It is observed, for instance, to rise each morning for a month in the constellation of the Ram, and for the next month in the Bull.