Under the Waves | Page 6

a slow ponderous tread.
A short iron ladder dipped from the gunwale of the barge a few feet down into the sea. The diver stepped upon this, turning with his face inwards, descended knee-deep into the water, and then stopped. Baldwin handed him the blasting-charge. At the same moment one of the supernumeraries advanced with the front-glass or bull's-eye in his hand, and the men at the pumps gave a turn or two to see that all was working well.
"All right?" demanded the supernumerary.
"Right," responded Maxwell, in a voice which issued sepulchrally from the iron globe.
There are three round windows fitted with thick plate-glass in the helmets to which we refer. The front one is made to screw off and on, and the fixing of this is always the last operation in completing a diver's toilet.
"Pump away," said the man, holding the round glass in front of Maxwell's nose, and looking over his shoulder to see that the order was obeyed. The glass was screwed on, and the man finished off by gravely patting Maxwell in an affectionate manner on the head.
"Why does he pat him so?" asked Edgar, with a laugh at the apparent tenderness of the act.
"It's a tinder farewell, I suppose," murmured Rooney, "in case he niver comes up again."
"It is to let him know that he may now descend in safety," answered Baldwin. "The pump there is kep' goin' from a few moments before the front-glass is screwed on till the diver shows his head above water again--which he'll do in quarter of an hour or so, for it don't take long to lay a charge; but our ordinary spell under water, when work is steady, is about four hours--more or less--with perhaps a breath of ten minutes once or twice at the surface when they're working deep."
"But why a breath at the surface?" asked Edgar. "Isn't the air sent down fresh enough?"
"Quite fresh enough, Mister Edgar, but the pressure when we go deep--say ten or fifteen fathoms--is severe on a man if long continued, so that he needs a little relief now and then. Some need more and some less relief, accordin' to their strength. Maxwell has only gone down fifteen feet, so that he wouldn't need to come up at all durin' a spell of work. We're goin' to blast a big rock that has bin' troublesome to us at low water. The hole was driven in it last week. We moored a raft over it and kep' men at work with a long iron jumper that reached from the rock to the surface of the sea. It was finished last night, and now he's gone to fix the charge."
"But I don't understand about the pressure, sur, at all at all," said Machowl, with a complicated look of puzzlement; "sure whin I putt my hand in wather I don't feel no pressure whatsomediver."
"Of course not," responded Baldwin, "because you don't put it deep enough. You must know that our atmosphere presses on our bodies with a weight of about 20,000 pounds. Well, if you go thirty-two feet deep in the sea you get the pressure of exactly another atmosphere, which means that you've got to stand a pressure all over your body of 40,000 when you've got down as deep as thirty-two feet."
"But," objected Rooney, "I don't fed no pressure of the atmosphere on me body at all."
"That's because you're squeezed by the air inside of you, man, as well as by the atmosphere outside, which takes off the feelin' of it, an', moreover, you're used to it. If the weight of our atmosphere was took off your outside and not took off your inside--your lungs an' the like,--you'd come to feel it pretty strong, for you'd swell like a balloon an' bu'st a'most, if not altogether."
Baldwin paused a moment and regarded the puzzled countenance of his pupil with an air of pity.
"Contrairywise," he continued, "if the air was all took out of your inside an' allowed to remain on your outside, you'd go squash together like a collapsed indyrubber ball. Well then, if that be so with one atmosphere, what must it be with a pressure equal to two, which you have when you go down to thirty-two feet deep in the sea? An' if you go down to twenty-five fathoms, or 150 feet, which is often done, what must the pressure be there?"
"Tightish, no doubt," said Rooney.
"True, lad," continued Joe. "Of course, to counteract this we must force more air down to you the deeper you go, so that the pressure inside of you may be a little more than the pressure outside, in order to force the foul air out of the dress through the escape-valve; and what between the one an' the other your sensations are peculiar, you may be sure.--But