“No, no, it does not seem to lose any, Harry; it only gains,” cried Rose, laughing.
Mulford was now satisfied, notwithstanding all that had passed on a previous occasion, that the laughing, bright-eyed, and quick-witted girl at his elbow, knew no more of the uses of a chronometer than her unusually dull and ignorant aunt; and he felt himself relieved from all embarrassment at once. Though he dared not even seem to distrust Mrs. Budd's intellect or knowledge before Rose, he did not scruple to laugh at Rose herself, to Rose. With her there was no jealousy on the score of capacity, her quickness being almost as obvious to all who approached her as her beauty.
“Rose Budd, you do not understand the uses of a chronometer, I see,” said the mate, firmly, “notwithstanding all I have told you concerning them.”
“It is to keep time, Harry Mulford, is it not?”
“True, to keep time—but to keep the time of a particular meridian; you know what meridian means, I hope?”
Rose looked intently at her lover, and she looked singularly lovely, for she blushed slightly, though her smile was as open and amicable as ingenuousness and affection could make it.
“A meridian means a point over our heads—the spot where the sun is at noon,” said Rose, doubtingly.
“Quite right; but it also means longitude, in one sense. If you draw a line from one pole to the other, all the places it crosses are on the same meridian. As the sun first appears in the east, it follows that he rises sooner in places that are east, than in places that are further west. Thus it is, that at Greenwich, in England, where there is an observatory made for nautical purposes, the sun rises about five hours sooner than it does here. All this difference is subject to rules, and we know exactly how to measure it.”
“How can that be, Harry? You told me this but the other day, yet have I forgotten it.”
“Quite easily. As the earth turns round in just twenty-four hours, and its circumference is divided into three hundred and sixty equal parts, called degrees, we have only to divide 360 by 24, to know how many of these degrees are included in the difference produced by one hour of time. There are just fifteen of them, as you will find by multiplying 24 by 15. It follows that the sun rises just one hour later, each fifteen degrees of longitude, as you go west, or one hour earlier each fifteen degrees of longitude as you go east. Having ascertained the difference by the hour, it is easy enough to calculate for the minutes and seconds.”