Fly's foot magnified.
"But, Uncle Philip, there is one thing yet hard to understand."
"What is it?"
"Why, the fly walks on the wall over our heads; now the air cannot press down upon his feet there."
"Very true, boys: it cannot press down, but it can and does press up against his feet; for the air presses up and down and sidewise all alike."
"Ah, now it is plain enough, and we are much obliged to you, Uncle Philip, for telling us what we wished to know."
"You are quite welcome, my dear boys, to all that I can teach you: if it makes you to be wiser and better men when you grow up, I shall be very thankful to God that I have been able to do you any good."
"Good morning, Uncle Philip."
"Good day, boys; I shall expect to see you all in church to-morrow."