Ben Zoof looked on in perplexity, regarding the lecturer with much the same curiosity as he would have watched the performances of a traveling mountebank at a fair in Montmartre; but Servadac and his two friends had already divined the professor’s meaning. They knew that French coinage is all decimal, the franc being the standard of which the other coins, whether gold, silver, or copper, are multiples or measures; they knew, too, that the caliber or diameter of each piece of money is rigorously determined by law, and that the diameters of the silver coins representing five francs, two francs, and fifty centimes measure thirty-seven, twenty-seven, and eighteen millimeters respectively; and they accordingly guessed that Professor Rosette had conceived the plan of placing such a number of these coins in juxtaposition that the length of their united diameters should measure exactly the thousand millimeters that make up the terrestrial meter.
The measurement thus obtained was by means of a pair of compasses divided accurately into ten equal portions, or decimeters, each of course 3.93 inches long. A lath was then cut of this exact length and given to the engineer of the Dobryna, who was directed to cut out of the solid rock the cubic decimeter required by the professor.
The next business was to obtain the precise weight of a kilogramme. This was by no means a difficult matter. Not only the diameters, but also the weights, of the French coins are rigidly determined by law, and as the silver five-franc pieces always weigh exactly twenty-five grammes, the united weight of forty of these coins is known to amount to one kilogramme.
“Oh!” cried Ben Zoof; “to be able to do all this I see you must be rich as well as learned.”
With a good-natured laugh at the orderly’s remark, the meeting adjourned for a few hours. By the appointed time the engineer had finished his task, and with all due care had prepared a cubic decimeter of the material of the comet.
“Now, gentlemen,” said Professor Rosette, “we are in a position to complete our calculation; we can now arrive at Gallia’s attraction, density, and mass.”
Everyone gave him his complete attention.
“Before I proceed,” he resumed, “I must recall to your minds Newton’s general law, ‘that the attraction of two bodies is directly proportional to the product of their masses, and inversely proportional to the square of their distances.’”
“Yes,” said Servadac; “we remember that.”
“Well, then,” continued the professor, “keep it in mind for a few minutes now. Look here! In this bag are forty five-franc pieces—altogether they weigh exactly a kilogramme; by which I mean that if we were on the earth, and I were to hang the bag on the hook of the steelyard, the indicator on the dial would register one kilogramme. This is clear enough, I suppose?”