lower and lower sank the submarine. there was a swirling and foaming of the water as she went down, caused by the air bubbles which the craft carried with her in her descent. only the top of the conning tower was out of water now, the ocean having closed over the deck and the rounded back of the boat. had any one been watching they would have imagined that an accident was taking place.

in the pilot house, with its thick glass windows, tom, his father and captain weston looked over the surface of the ocean, which every minute was coming nearer and nearer to them.

"we'll be all under in a few seconds," spoke tom in a solemn voice, as he listened to the water hissing into the tanks.

"yes, and then we can see what sort of progress we will make," added mr. swift. "everything is going fine, though," he went on cheerfully. "i believe i have a good boat."

"there is no doubt of it in my mind," remarked captain weston, and tom felt a little disappointed that the sailor did not shout out some such expression as "shiver my timbers!" or "keel-haul the main braces, there, you lubber!" but captain weston was not that kind of a sailor, though his usually quiet demeanor could be quickly dropped on necessity, as tom learned later.

a few minutes more and the waters closed over the top of the conning tower. the advance was completely submerged. through the thick glass windows of the pilot house the occupants looked out into the greenish water that swirled about them; but it could not enter. then, as the boat went lower, the light from above gradually died out, and the semi-darkness gave place to gloom.

"turn on the electrics and the searchlight, tom," directed his father.

there was the click of a switch, and the conning tower was flooded with light. but as this had the effect of preventing the three from peering out into the water, just as one in a lighted room cannot look out into the night, tom shut them off and switched on the great searchlight. this projected its powerful beams straight ahead and there, under the ocean, was a pathway of illumination for the treasure-seekers.

"fine!" cried captain weston, with more enthusiasm than he had yet manifested. "that's great, if you don't mind me mentioning it. how deep are we?"

tom glanced at a gage on the side of the pilot tower.

"only about sixty feet," he answered.

"then don't go any deeper!" cried the captain hastily. "i know these waters around here, and that's about all the depth you've got. you'll be on the bottom in a minute."

"i intend to get on the bottom after a while," said mr. swift, "but not here. i want to try for a greater distance under water before i come to rest on the ocean's bed. but i think we are deep enough for a test. tom, close the tank intake pipes and we'll see how the advance will progress when fully submerged."

the hissing stopped, and then, wishing to see how the motors and other machinery would work, the aged inventor and his son, accompanied by captain weston, descended from the conning tower, by means of an inner stairway, to the interior of the ship. the submarine could be steered and managed from below or above. she was now floating about sixty-five feet below the surface of the bay.

"well, how do you like it?" asked tom of mr. damon, as he saw his friend in an easy chair in the living-room or main cabin of the craft, looking out of one of the plate-glass windows on the side.

"bless my spectacles, it's the most wonderful thing i ever dreamed of!" cried the queer character, as he peered at the mass of water before him. "to think that i'm away down under the surface, and yet as dry as a bone. bless my necktie, but it's great! what are we going to do now?"

"go forward," replied the young inventor.

"perhaps i had better make an observation," suggested captain weston, taking his telescope from under his arm, where he had carried it since entering the craft, and opening it. "we may run afoul of something, if you don't mind me mentioning such a disagreeable subject." then, as he thought of the impossibility of using his glass under water, he closed it.

"i shall have little use for this here, i'm afraid," he remarked with a smile. "well, there's some consolation. we're not likely to meet many ships in this part of the ocean. other vessels are fond enough of remaining on the surface. i fancy we shall have the depths to ourselves, unless we meet a government submarine, and they are hardly able to go as deep as we can. no, i guess we won't run into anything and i can put this glass away."

"unless we run into berg and his crowd," suggested tom in a low voice.

"ha! ha!" laughed captain weston, for he did not want mr. swift to worry over the unscrupulous agent. "no, i don't believe we'll meet them, tom. i guess berg is trying to work out the longitude and latitude i gave him. i wish i could see his face when he realizes that he's been deceived by that fake map."

"well, i hope he doesn't discover it too soon and trail us," went on the lad. "but they're going to start the machinery now. i suppose you and i had better take charge of the steering of the craft. dad will want to be in the engine-room."

"all right," replied the captain, and he moved forward with the lad to a small compartment, shut off from the living-room, that served as a pilot house when the conning tower was not used. the same levers, wheels and valves were there as up above, and the submarine could be managed as well from there as from the other place.

"is everything all right?" asked mr. swift as he went into the engine-room, where garret jackson and mr. sharp were busy with oil cans.

"everything," replied the balloonist. "are you going to start now?"

"yes, we're deep enough for a speed trial. we'll go out to sea, however, and try for a lower depth record, as soon as there's enough water. start the engine."

a moment later the powerful electric currents were flowing into the forward and aft plates, and the advance began to gather way, forging through the water.

"straight ahead, out to sea, tom," called his father to him.

"aye, aye, sir," responded the youth.

"ha! quite seaman-like, if you don't mind a reference to it," commented captain weston with a smile. "mind your helm, boy, for you don't want to poke her nose into a mud bank, or run up on a shoal."

"suppose you steer?" suggested the lad. "i'd rather take lessons for a while."

"all right. perhaps it will be safer. i know these waters from the top, though i can't say as much for the bottom. however, i know where the shoals are."

the powerful searchlight was turned, so as to send its beams along the path which the submarine was to follow, and then, as she gathered speed, she shot ahead, gliding through the waters like a fish.

mr. damon divided his time between the forward pilot-room, the living-apartment, and the place where mr. swift, garret jackson and mr. sharp were working over the engines. every few minutes he would bless some part of himself, his clothing, or the ship. finally the old man settled down to look through the plate-glass windows in the main apartment.

on and on went the submarine. she behaved perfectly, and was under excellent control. some times tom, at the request of his father, would send her toward the surface by means of the deflecting rudder. then she would dive to the bottom again. once, as a test, she was sent obliquely to the surface, her tower just emerging, and then she darted downward again, like a porpoise that had come up to roll over, and suddenly concluded to seek the depths. in fact, had any one seen the maneuver they would have imagined the craft was a big fish disporting itself.

captain weston remained at tom's side, giving him instructions, and watching the compass in order to direct the steering so as to avoid collisions. for an hour or more the craft was sent almost straight ahead at medium speed. then mr. swift, joining his son and the captain, remarked:

"how about depth of water here, captain weston?"

"you've got more than a mile."

"good! then i'm going down to the bottom of the sea! tom, fill the tanks still more.

"aye, aye, sir," answered the lad gaily. "now for a new experience!"

"and use the deflecting rudder, also," advised his father. "that will hasten matters."

five minutes later there was a slight jar noticeable.

"bless my soul! what's that?" cried mr. damon. "have we hit something?"

"yes," answered tom with a smile.

"what, for gracious sake?"

"the bottom of the sea. we're on the bed of the ocean."