At that moment Westby coughed—­an unnatural cough.  And instantly a miracle happened; every single wooden eraser—­there were half a dozen of them—­leaped from its place on the shelf beneath the blackboard and tumbled clattering down the steps to the floor.  At the same instant Westby flung up both arms, tottered on the topmost step, and succeeded in regaining his poise with apparently great difficulty.

The class giggled.

“Mr. Upton, sir!  Mr. Upton, sir!” cried Westby excitedly.  “Did you feel the earthquake?  It was very noticeable on this side of the room.  Do you think it’s safe for us to stay indoors, sir?  There may be another shock!”

“Westby,” Irving’s voice had a nervous thrill that for the moment quieted the laughter, “did you cause those erasers to be pulled down?”

“Did I cause them to be pulled down?  I don’t understand, sir.  How could I, sir?  Six of them all at once!”

“Bring me one of those erasers, please.”

Westby stooped; there was a sound of snapping string.  Then he came forward and presented the eraser.

“You tied string to all these erasers, did you?” Irving examined the fragment that still clung to the object.  “And then arranged to have them pulled down?”

“You see how short that string is, sir; nobody could have reached it to pull it.  Didn’t you feel the earthquake, sir?  Didn’t you see how it almost threw me off my feet?  Really, I don’t believe it’s quite safe to stay here—­”

“You may be right; I shouldn’t wonder at all if there was a second shock coming to you soon,” said Irving, and the subdued chuckle that went round the class told him he had scored.  “You may now demonstrate to the class the Theorem assigned you.”

“Yes, sir.”  Westby turned and took up the pointer.

“We have here,” he began, “the two triangles I C U and J A Y—­with the angle I C U of the one equal to the angle J A Y of the other.”  The class tittered; Westby went on glibly, bending the lath-like pointer between his hands:  “Let us now erect the angle K I D, equal to the angle I C U; then the angle K I D will also be equal to the angle J A Y—­things equal to the same thing are equal to each other.”

Westby stopped to turn a surprised, questioning look upon the snickering class.

“Yes, that will do for that demonstration,” said Irving.  He rose from his seat; his lips were trembling, and the laughter of the class ceased.  “You may leave the room—­for your insolence—­at once!”

He had meant to be dignified and calm, but his anger had rushed to the surface, and his words came in a voice that suggested he was on the verge of tears.

“I beg your pardon, sir, but I don’t think I quite understand,” said Westby suavely.

“You understand well enough.  I ask you to leave the room.”

“I’m afraid, Mr. Upton, that my little pleasantries—­usually considered harmless—­do not commend themselves to you.  But you hurt my feelings very much, sir, when you apply such a harsh word as insolence to my whimsical humor—­”