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?"

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 technicalignorance, 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."
But Rosette did not take the slightest notice of the interruption.

"A substance it is which no doubt constitutes the sole material
of the comet, extending from its surface to its innermost depths.

The probability is that it would be so; your experience confirms
that probability: you have found no trace of any other substance.

Of this rock here is a solid decimeter; let us get at its weight,
and we shall have the key which will unlock the problem of

the whole weight of Gallia. We have demonstrated that the force
of attraction here is only one-seventh of what it is upon the earth,

and shall consequently have to multiply the apparent weight
of our cube by seven, in order to ascertain its proper weight.

Do you understand me, goggle-eyes?"
This was addressed to Ben Zoof, who was staring hard at him.

"No!" said Ben Zoof.
"I thought not; it is of no use waiting for your puzzle-brains

to make it out. I must talk to those who can understand."
The professor took the cube, and, on attaching it to the hook

of the steelyard, found that its apparent weight was one kilogramme
and four hundred and thirty grammes.

"Here it is, gentlemen; one kilogramme, four hundred and thirty grammes.
Multiply that by seven; the product is, as nearly as possible,

ten kilogrammes. What, therefore, is our conclusion? Why, that the
density of Gallia is just about double the density of the earth,

which we know is only five kilogrammes to a cubic decimeter.
Had it not been for this greater density, the attraction of Gallia

would only have been one-fifteenth instead of one-seventh of
the terrestrial attraction."

The professor could not refrain from exhibiting his gratification that,
however inferior in volume, in density, at least, his comet had the advantage

over the earth.
Nothing further now remained than to apply the investigations

thus finished to the determining of the mass or weight.
This was a matter of little labor.

"Let me see," said the captain; "what is the force of gravity
upon the various planets?"

"You can't mean, Servadac, that you have forgotten that?
But you always were a disappointing pupil."

The captain could not help himself: he was forced to confess
that his memory had failed him.

"Well, then," said the professor, "I must remind you.
Taking the attraction on the earth as 1, that on Mercury

is 1.15, on Venus it is .92, on Mars .5, and on Jupiter 2.45;
on the moon the attraction is .16, whilst on the surface of

the sun a terrestrial kilogramme would weigh 28 kilogrammes."
"Therefore, if a man upon the surface of the sun were to fall down,

he would have considerable difficulty in getting up again.
A cannon ball, too, would only fly a few yards," said Lieutenant Procope.

"A jolly battle-field for cowards!" exclaimed Ben Zoof.
"Not so jolly, Ben Zoof, as you fancy," said his master;

"the cowards would be too heavy to run away."
Ben Zoof ventured the remark that, as the smallness of Gallia

secured to its inhabitants such an increase of strength and agility,
he was almost sorry that it had not been a little smaller still.

"Though it could not anyhow have been very much smaller,"
he added, looking slyly at the professor.