“Perfectly. Nicholl and I would have made it, if the observatory had not saved us the trouble.” “Very well, old Barbicane,” replied Michel; “they might have cut off my head, beginning at my feet, before they could have made me solve that problem.” “Because you do not know algebra,” answered Barbicane quietly. “Ah, there you are, you eaters of _x_1; you think you have said all when you have said ‘Algebra.’” “Michel,” said Barbicane, “can you use a forge without a hammer, or a plow without a plowshare?” “Hardly.” “Well, algebra is a tool, like the plow or the hammer, and a good tool to those who know how to use it.” “Seriously?” “Quite seriously.” “And can you use that tool in my presence?” “If it will interest you.” “And show me how they calculated the initiatory speed of our car?” “Yes, my worthy friend; taking into consideration all the elements of the problem, the distance from the center of the earth to the center of the moon, of the radius of the earth, of its bulk, and of the bulk of the moon, I can tell exactly what ought to be the initiatory speed of the projectile, and that by a simple formula.” “Let us see.” “You shall see it; only I shall not give you the real course drawn by the projectile between the moon and the earth in considering their motion round the sun. No, I shall consider these two orbs as perfectly motionless, which will answer all our purpose.” “And why?” “Because it will be trying to solve the problem called ‘the problem of the three bodies,’ for which the integral calculus is not yet far enough advanced.” “Then,” said Michel Ardan, in his sly tone, “mathematics have not said their last word?” “Certainly not,” replied Barbicane. “Well, perhaps the Selenites have carried the integral calculus farther than you have; and, by the bye, what is this ‘integral calculus?’” “It is a calculation the converse of the differential,” replied Barbicane seriously. “Much obliged; it is all very clear, no doubt.” “And now,” continued Barbicane, “a slip of paper and a bit of pencil, and before a half-hour is over I will have found the required formula.” Half an hour had not elapsed before Barbicane, raising his head, showed Michel Ardan a page covered with algebraical signs, in which the general formula for the solution was contained. “Well, and does Nicholl understand what that means?” “Of course, Michel,” replied the captain. “All these signs, which seem cabalistic to you, form the plainest, the clearest, and the most logical language to those who know how to read it.” “And you pretend, Nicholl,” asked Michel, “that by means of these hieroglyphics, more incomprehensible than the Egyptian Ibis, you can find what initiatory speed it was necessary to give the projectile?” “Incontestably,” replied Nicholl; “and even by this same formula I can always tell you its speed at any point of its transit.” “On your word?” “On my word.” “Then you are as cunning as our president.”