“If, therefore, there is any reason for alarm, it is not, in my opinion, because we are to apprehend the penetration of the gaseous mass of carbonic-oxide into our atmosphere, but a rise in temperature, which cannot fail to result from the transformation of mechanical motion into heat. If this be so, safety may be perhaps attained by taking refuge on the side of the globe opposed to that which is to experience the direct shock of the comet, for the air is a very bad conductor of heat.” The permanent secretary of the academy rose in his turn. A worthy successor to the Fontenelles and Aragos of the past, he was not only a man of profound knowledge, but also an elegant writer and a persuasive orator, rising sometimes even to the highest flights of eloquence. “To the theory which we have just heard,” he said, “I have nothing to add; I can only apply it to the case of some comet already known. Let us suppose, for example, that a comet of the dimensions of that of 1811 should collide squarely with the earth in its path about the sun. The terrestrial ball would penetrate the nebula of the comet without experiencing any very sensible resistance. Admitting that this resistance is very slight, and that the density of the comet’s nucleus may be neglected, the passage of the earth through the head of a comet of 1,800,000 kilometers in diameter, would require at least 25,000 seconds—that is, 417 minutes, or six hours, fifty-seven minutes—in round numbers, seven hours—the velocity being 120 times greater than that of a cannon-ball; and the earth continuing to rotate upon its axis, the collision would commence about six o’clock in the morning. [Illustration] “Such a plunge into the cometary ocean, however rarified it might be, could not take place without producing as a first and immediate consequence, by reason of the thermodynamic principles which have been just called to your attention, a rise in temperature such that probably our entire atmosphere would take fire! It seems to me that in this particular case the danger would be very serious. “But it would be a fine spectacle for the inhabitants of Mars, and a finer one still for those of Venus. Yes, that would indeed be a magnificent spectacle, analogous to those we have ourselves seen in the heavens, but far more splendid to our near neighbors.