“No, no!” suggested a compassionate soul behind me.

“No, sir!” said I.

“Explain yourself. In what sort of a triangle?”

“A right-angled triangle,” whispered the prompting voice.

“A right-angled triangle,” I repeated, like a parrot.

“Silence there, behind!” shouted the Professor; and then continued, turning to me, “Then, according to you, the big square is equal to each of the smaller ones?”

Good gracious! the thing was absurd. But I had a happy inspiration.

“No, sir, to both of them added together.”

“To the sum then,—say to the sum. And you should say equivalent, not equal. Now demonstrate.”

I was in a cold perspiration—icy cold—despite the tropical temperature. I looked stupidly at the right-angled triangle, the square of the hypothenuse, and its two subsidiary squares; I passed the chalk from one hand to the other and back again, and said nothing, for the very good reason that I had nothing to say.