Now, if a navigator had to depend only on the meridian lines indicating distance east and west, he might be almost any distance north or south of where he wanted to go.So the earth is further divided into sections by other imaginary lines called parallels of latitude.As all know, these indicate the distance north or south of the middle line, or the equator.The equator goes around the earth at the middle, so to speak, running from east to west, or from west to east, according as it is looked at.The meridian of Greenwich may be regarded as a sort of half equator, running half way around the earth in exactly the opposite direction, or from north to south.
The place where any two of these imaginary lines, crossing at right angles, meet may be exactly determined by the science of navigation.It is a complicated and difficult science, but by calculating the distance of thesun above the horizon, sometimes by views of stars, by knowing the speed of the ship, and by having the exact astronomical time at hand, shown on an accurate chronometer, the exact position of a ship at any hour may be determined.
By this means, if a navigator wants to get to a place where two certain lines cross, indicating an exact spot in the ocean, he is able to do so.He can tell for instance when he has reached the place where the seventy- second degree of longitude, west from Greenwich, meets and crossed the twentieth parallel of latitude.This spot is just off the northern coast of Haiti.Other positions are likewise determined.
It was after about an hour of rather slow progress on the surface of the calm sea, no excess speed being used for fear of over-running the mark, that Tom and his associates gathered on deck again to make another calculation.
Long and carefully they worked out their position, and when, at last, the figures had been checked and checked again, to obviate the chance of another error, the young inventor exclaimed:
"Well, we're here!" "Really?" cried Ned.
"No doubt of it," said his chum.
"Bless my doormat!" cried Mr.Damon."And do you mean to say, Tom Swift, that if we submerge now we'll be exactly where the Pandora lies, a wreck on the floor of the ocean"I mean to say that we're at exactly the spot Where Hardley said she went down," corrected Tom, "and we weren't there before --that is not so that we actually knew it.Now we are, and we're going down.But that doesn't guarantee that we'll find the wreck.She may have shifted, or be covered with sand.All that I said before in reference to the difficulty in locating something under the surface of the sea still holds good."Once more, to make very certain there was no error, the figures were gone over, Then, as one result checked the other, Tom put away the papers, the nautical almanac, and said:
"Let's go!"
Slowly the tanks of the M.N.1 began to fill.It was decided to let hersink straight down, instead of descending by means of the vertical rudders.In that way it was hoped to land her as nearly as possible on the exact spot where the Pandora was supposed to be.
"How deep will it be, Tom?" asked Ned, as he stood beside his chum in the forward observation cabin and watched the needle of the gauge move higher and higher.
"About six hundred feet, I judge, going by the character of the sea bottom around here.Certainly not more than eight hundred I should say." And Tom was right.At seven hundred and eighty-six feet the gauge stopped moving, and a slight jar told all on board that the submarine was again on the ocean floor.
"Now to look for the wreck!" exclaimed Tom."And it will be a real search this time.We know we are starting right.""Are you going to put on diving suits and walk around looking for her?" asked Ned.
"No, that would take too long," answered Tom."We'll just cruise about, beginning with small circles and gradually enlarging them, spiral fashion.We'll have to go up a few feet to get off the bottom."As Tom was about to give this order Ned looked from the glass windows.The powerful searchlight had been switched on and its gleams illuminated the ocean in the immediate vicinity of the craft.
As was generally the case, the light attracted hundreds of fish of various shapes, sizes, and, since the waters were tropical, beautiful colors.They swarmed in front of the glass windows, and Ned was glad to note that there were no large sea creatures, like horse mackerel or big sharks.Somehow or other, Ned had a horror of big fish.There were sharks in the warm waters, he well knew, but he hoped they would keep away, even though he did not have to encounter any in the diving suit.
Slowly the submarine began to move.And as she was being elevated slightly above the ocean bed, to enable her to proceed, Ned uttered an exclamation and pointed to the windows.
"Look, Tom!" he cried.
"What is it?" the young inventor asked.
"Snakes!" whispered his chum."Millions of 'em! Out there in thewater! Look how they're writhing about!" Tom Swift laughed.
"Those aren't snakes!" he said."That's serpent grass--a form of very long seaweed which grows on certain bottoms.It attains a length of fifty feet sometimes, and the serpent weed looks a good deal like a nest of snakes.That's how it got its name.I didn't know there was any here.But we must have dropped down into a bed of it.""Any danger?" asked Ned.
"Not that I know of, only it may make it more difficult for us to see the wreck of the Pandora."As Tom turned to leave the cabin the submarine suddenly ceased moving.And she came to a gradual stop as though she had been "snubbed" by a mooring line.
"I wonder what's the matter!" exclaimed Tom."We can't have come upon the wreck so soon."At that moment a man entered the cabin."Trouble, Mr.Swift!" he reported."What kind?" asked Tom.
"Our propellers are tangled with a mass of serpent weed," was the answer."They're both fouled, and we can't budge.""Bless my anchor chain!" ejaculated Mr.Damon."Stuck again!"
