termined 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?"

As he spoke the professor designedly kept his eyes fixed upon Ben Zoof.
He was avowedly following the example of Arago,