Читать книгу Across India; Or, Live Boys in the Far East - Oliver 1822-1897 Optic - Страница 11
ABOUT FINDING THE LONGITUDE
Оглавление"Well, Captain Scott, what is the run to-day?" asked Louis Belgrave, the owner of the steam-yacht Guardian-Mother, which had at this date made her way by a somewhat devious course half way round the world, and was in the act of making the other half.
The young magnate was eighteen years old, and was walking on the promenade deck of the steamer with a beautiful young lady of sixteen when he asked for information in regard to the run, or the distance made by the ship during the last sea-day.
"Before I answer your question, my dear Louis, I must protest against being any longer addressed as captain, for I am not now entitled to that honorable appellation," replied the young man addressed by the owner.
"Once a captain always a captain," replied Louis. "One who has been a member of Congress is still an 'Honorable,' though his term of office expired twenty or forty years ago. The worthy commander of the Guardian-Mother was always called Captain Ringgold in Von Blonk Park and New York, though he had not been in command of a ship for ten years," argued Louis.
"That's right; but the circumstances are a little different in my case. In the first place, I am only eighteen years old, and my brief command was a very small one, as the world goes. It hardly entitles me to be called captain after I have ceased to be in command. In charge of the little Maud I was the happiest young fellow on the Eastern Continent; but I am just as happy now, for this morning I was formally appointed third officer of the Guardian-Mother, at the wages paid to Captain Sharp when he had the same position."
"I congratulate you, Mr. Scott," said Louis, grasping the hand of the new officer, though he had been duly consulted in regard to the appointment the day before.
"Permit me to congratulate you also, Mr. Scott," added Miss Blanche, as she extended to him her delicate little hand.
"Thank you, Miss Woolridge," replied the new third officer, raising the uniform cap he had already donned, and bowing as gracefully as a dancing-master. "Thank you with all my heart, Louis. I won't deny that I was considerably broken up when the Maud was sold; but now I am glad of it, for it has given me a position that I like better."
"Now, Mr. Scott, what is the run for to-day?" asked Louis, renewing his first question.
"I don't know," replied the third officer with a mischievous smile.
"You don't know!" exclaimed Louis.
"I do not, Louis."
"I thought all the officers, including the commander, took the observation, and worked up the reckoning for the . We got eight bells nearly an hour ago, and the bulletin must have been posted by this time."
"It was posted some time ago. All the officers work up the reckoning; and I did so with the others. The commander and I agreed to a second."
"What do you mean by saying you do not know the run?" demanded Louis.
"I do know the run; but that was not what you asked me," answered Scott with the same mischievous smile.
"What did I ask you?"
"The first time you asked me all right, and I should have answered you if I had not felt obliged to switch off and inform you and Miss Woolridge of my new appointment. The second time you put it you changed the question."
"I changed it?" queried Louis.
"You remember that when Mrs. Blossom asked Flix where under the sun he had been, he replied that he had not been anywhere, as it happened to be in the evening, when the sun was not overhead."
"A quibble!" exclaimed Louis, laughing.
"Granted; but one which was intended to test your information in regard to a nautical problem. You asked me the second time for the run of to-day for the last twenty-four hours."
"And that was what I asked you the first time," answered Louis.
"I beg your pardon, but you asked me simply for the run to-day."
"Isn't that the same thing?"
"Will you please to tell me how many hours there are in a sea-day?" asked Scott, becoming more serious.
"That depends," answered Louis, laughing. "You have me on the run."
"You will find that the bulletin signed by the first officer gives the run as 330 miles; but the answer to your second question is 337 miles, about," added the third officer. "Just here the day is only twenty-three hours and forty minutes long as we are running; and the faster we go the shorter the day," continued the speaker, who was ciphering all the time on a card.
"I don't see how that can be," interposed Miss Blanche, with one of her prettiest smiles.
"There is the lunch-bell; but I shall be very happy to explain the matter more fully later in the day, Miss Woolridge, unless you prefer that Louis should do it," suggested Scott.
"I doubt if I could do it, and I should be glad to listen to the explanation," replied Louis, as they descended to the main cabin; for the new third officer was permitted to retain his place at the table as well as his state-room.
The commander had suggested that there was likely to be some change of cabin arrangements; for it was not in accordance with his ideas of right that the third officer should be admitted to the table, while the first and second were excluded; and Louis was very desirous that his friend Scott should remain in the cabin. The repasts on board the steamer were social occasions, and the party often sat quite an hour at the table, as at the present luncheon. But as soon as the company left their places, Louis and Miss Blanche followed the third officer to the promenade deck, to hear the desired explanation of sea-time.
"Of course you know how the longitude of the ship is obtained, Miss Woolridge?" the young officer began.
"Papa explained it to me once, but I could not understand it," replied the fair maiden.
"Then we will explain that first. One of the great circles extending through the poles is called the prime meridian; and any one may be selected, though that of Greenwich has been almost universally adopted. This place is near London. From this prime meridian longitude is calculated, which means that any given locality is so many degrees east or west of it. Sandy Hook is in longitude 74°, or it is that number of degrees west of Greenwich. Aden is in 45° east longitude."
"Then you find how many miles it is by multiplying the number of degrees by 69," suggested Miss Blanche.
"You have forgotten about knots, or sea-miles," said Louis.
"So I have! I should have said multiply by 60," added the young lady.
"That would not do it any better," replied Scott.
"Degrees of latitude are always the same for all practical purposes; but degrees of longitude are as--
'Variable as the shade
By the light quivering aspen made,'"
continued the third officer, who was about to say "as a woman's mind;" but he concluded that it was not quite respectful to the lovely being before him.
"What a poetical sea-monster you are, Mr. Scott!" exclaimed Miss Blanche with a silvery laugh.
"I won't do so any more," Scott protested, and then continued his explanation. "Degrees of longitude vary from nothing at the poles, up to 69.07 statute, or 60 geographical or sea-miles, at the equator. We are now in about 15° north latitude; and a degree of longitude is 66.65 statute miles, or 57.9855 sea-miles, near enough to call it 58. By the way, Louis, multiply the number of statute miles by .87, and it gives you the sea-miles. Divide the knots by the same decimal, and it gives the statute miles."
"I will try to remember that decimal as you have done," replied Louis. "Now, Mr. Scott, don't open Bowditch's Navigator to us, or talk about projection,' 'logarithms,' 'Gunter,' and 'inspection;' for I am not capable of understanding them, for my trigonometry has gone to the weeping willows."
"Talk to us in English, Mr. Scott," laughed Miss Blanche.
"Let us go up to Conference Hall, where there is a table," said the third officer, as he produced a book he had brought up from his state-room. He led the way to the promenade, where he spread out a chart in the "Orient Guide," which had twenty-six diagrams of a clock, one at the foot of every fifteen degrees of longitude. At this point the commander came upon the promenade.
"Formerly the figures on a timepiece in Italy, and perhaps elsewhere, went up to twenty-four, instead of repeating the numbers up to twelve; and these diagrams are constructed on that plan," continued Scott.
"An attempt has been made to re-establish this method in our own country. I learned once from a folder that a certain steamer would leave Detroit at half-past twenty-two; meaning half-past ten. But the plan was soon abandoned," interposed the captain.
"Aden, from which we sailed the other day, is in longitude 45° east. Every degree by meridians is equal to four minutes of clock-time. Multiply the longitude by four, and the result in minutes is the difference of time between Greenwich and Aden, 180 minutes, or three hours. When it is noon at Greenwich, it is three o'clock at Aden, as you see in the diagram before you."
"Three o'clock in the morning, Mr. Scott?" queried the commander.
"In the afternoon, I should have added. Going east the time is faster, and vice versa," continued the young officer. "At our present speed our clocks must be put about twenty minutes ahead, for a third of an hour has gone to Davy Jones's locker."
"I understand all that perfectly," said Miss Blanche with an air of triumph.
"You will be a sea-monster before you get home. The sirens were beautiful, and sang very sweetly," added Scott jocosely.
"They were wicked, and I don't want to be one. But I do not quite understand how you found out what time it was at noon to-day," added the young lady.
"For every degree of longitude sailed there is four minutes' difference of clock-time," Scott proceeded. "You know that a chronometer is a timepiece so nicely constructed and cared for, that it practically keeps perfect time. Meridians are imaginary great circles, and we are always on one of them. With our sextants we find when the centre of the sun is on the celestial meridian corresponding to the terrestrial one; and at that instant it is noon where we are. Then we know what time it is. We compare the time thus obtained with that indicated by the chronometer, and find a difference of four hours."
"I see it all!" exclaimed the fair maiden, as triumphantly as though she had herself reasoned out the problem. "Four hours make 240 minutes, and four minutes to a degree gives 60° as the longitude.
"Quite correct, Miss Woolridge," added Scott approvingly.
"If I could only take the sun, I could work up the longitude myself," the little beauty declared.
"You have already taken the son," replied Scott; but he meant the son of Mrs. Belgrave, and he checked himself before he had "put his foot in it;" for Louis would have resented such a remark.
"I have seen them do it, but I never took the sun myself," protested the maiden.
The sea had suddenly begun to make itself felt a few hours before, and a flood of spray was cast over the promenade, which caused the party to evacuate it, and move farther aft. It was the time of year for the north-east monsoons to prevail, and the commander had declared that the voyage would probably be smooth and pleasant all the way to Bombay. It did not look much like it when the ship began to roll quite violently.