“Oh, certainly, certainly!” the Professor replied with a smile on his jolly face. “Allow me to explain. It is, in fact, a very simple problem in Hydrodynamics. (That means a combination of Water and Strength.) If we take a plunge-bath, and a man of great strength (such as myself) about to plunge into it, we have a perfect example of this science. I am bound to admit,” the Professor continued, in a lower tone and with downcast eyes, “that we need a man of remarkable strength. He must be able to spring from the floor to about twice his own height, gradually turning over as he rises, so as to come down again head first.” “Why, you need a flea, not a man!” exclaimed the Sub-Warden. “Pardon me,” said the Professor. “This particular kind of bath is not adapted for a flea. Let us suppose,” he continued, folding his table-napkin into a graceful festoon, “that this represents what is perhaps the necessity of this Age--the Active Tourist's Portable Bath. You may describe it briefly, if you like,” looking at the Chancellor, “by the letters A.T.P.B.” The Chancellor, much disconcerted at finding everybody looking at him, could only murmur, in a shy whisper, “Precisely so!” “One great advantage of this plunge-bath,” continued the Professor, “is that it requires only half-a-gallon of water--” “I don't call it a plunge-bath,” His Sub-Excellency remarked, “unless your Active Tourist goes right under!” “But he does go right under,” the old man gently replied. “The A.T. hangs up the P. B. on a nail--thus. He then empties the water-jug into it--places the empty jug below the bag--leaps into the air--descends head-first into the bag--the water rises round him to the top of the bag--and there you are!” he triumphantly concluded. “The A.T. is as much under water as if he'd gone a mile or two down into the Atlantic!” “And he's drowned, let us say, in about four minutes--” “By no means!” the Professor answered with a proud smile. “After about a minute, he quietly turns a tap at the lower end of the P. B.--all the water runs back into the jug and there you are again!” “But how in the world is he to get out of the bag again?” “That, I take it,” said the Professor, “is the most beautiful part of the whole invention. All the way up the P.B., inside, are loops for the thumbs; so it's something like going up-stairs, only perhaps less comfortable; and, by the time the A. T. has risen out of the bag, all but his head, he's sure to topple over, one way or the other--the Law of Gravity secures that. And there he is on the floor again!” “A little bruised, perhaps?” “Well, yes, a little bruised; but having had his plunge-bath: that's the great thing.” “Wonderful! It's almost beyond belief!” murmured the Sub-Warden. The Professor took it as a compliment, and bowed with a gratified smile.