As he spoke the professor designedly kept his eyes fixed upon Ben Zoof. He was avowedly following the example of Arago, who was accustomed always in lecturing to watch the countenance of the least intelligent of his audience, and when he felt that he had made his meaning clear to him, he concluded that he must have succeeded with all the rest. In this case, however, it was technical ignorance, rather than any lack of intelligence, that justified the selection of the orderly for this special attention.
Satisfied with his scrutiny of Ben Zoof’s face, the professor went on. “And now, gentlemen, we have to see what these coins weigh here upon Gallia.”
He suspended the money bag to the hook; the needle oscillated, and stopped. “Read it off!” he said.
The weight registered was one hundred and thirty-three grammes.
“There, gentlemen, one hundred and thirty-three grammes! Less than one-seventh of a kilogramme! You see, consequently, that the force of gravity here on Gallia is not one-seventh of what it is upon the earth!”
“Interesting!” cried Servadac, “most interesting! But let us go on and compute the mass.”
“No, captain, the density first,” said Rosette.
“Certainly,” said the lieutenant; “for, as we already know the volume, we can determine the mass as soon as we have ascertained the density.”
The professor took up the cube of rock. “You know what this is,” he went on to say. “You know, gentlemen, that this block is a cube hewn from the substance of which everywhere, all throughout your voyage of circumnavigation, you found Gallia to be composed—a substance to which your geological attainments did not suffice to assign a name.”
“Our curiosity will be gratified,” said Servadac, “if you will enlighten our ignorance.”