“A cloud if you like, Willis; but do you know the weight of it you carry on your shoulders?”

“Well, it cannot be very great, otherwise I should feel it.”

“What do you say to a ton or so, old fellow?”

“If you wish me to believe that, you will have to explain how, where, when, why, and wherefore.”

“Very good.  Willis; you have bathed sometimes?”

“Yes, certainly.”

“In the sea?”

“Yes.”

“Do you know what water weighs?”

“No, but I know that it is heavy.”

“Well, a square yard of air weighs two pounds and a half, but a square yard of water weighs two thousand pounds.  Now, can you calculate the weight of the water that is on your back and pressing on your sides when you swim?”

“No, I cannot.”

“You are not sufficiently up in arithmetic to do that, Willis?”

“No.”

“Nor am I either, Willis; but let me ask you how it is that the waves do not carry you along with them?”

“Because one wave neutralises the effect of another.”

“Very good; but how is it that these ponderous waves, coming down upon you, do not crush you to atoms by their mere weight?”

“Well, I suppose that liquids do not operate in the same way as solids:  perhaps there is something in our bodies that counterbalances the effect of the water.”

“Very likely; and if such be the case as regards water, may it not be so also as regards air?”

“But I do not feel air; whereas, if I go into water, I not only feel it, but taste it sometimes, and I cannot force my way through it without considerable exertion.”

“That is because you are organized to live in air and not in water.  You ask the smallest sprat or sticklebake if it does not, in the same way feel the air obstruct its progress.”

“But would the stickleback answer me, Master Fritz?”

“Why not, if it is polite and well bred?”

“By the way, Willis,” inquired Jack, “do you ever recollect having lived without breathing?”

“Can’t say I do.”

“Very well, then; had you felt the weight of the air at any given moment, it must have produced an impression you never felt before, but you have not, because circumstances have never varied.  A sensation supposes a contrast, whilst, ever since you existed, you have always been subject to atmospheric pressure.”

“Ah, now I begin to get at the gist of your argument.  You mean, for example, that I would never have appreciated the delicate flavor of Maryland or Havanna, had I not been accustomed to smoke the cabbage-leaf manufactured in Whitechapel.”

“Precisely so; and take for another example the farm of Antisana, which is situated about midway up the Cordilleras, mountains of South America.  When travellers, arriving there from the summits which are covered with perpetual snow, meet others arriving from the plain where the heat is intense, those that descend are invariably bathed in perspiration, whilst those that have come up are shivering with cold and covered with furs.  The reason of this is, that we cannot feel warm till we have been cold, and vice versa.”