LUMEN. The paradox is only apparent. The laws of sound are essentially different from the laws of light. Sound travels only at the rate of 340 metres a second, and its effects have absolutely nothing in common with those of light. Nevertheless it is evident that if we were to advance into the air with a velocity _superior_ to that of sound, we should hear inversely the sounds that left the lips of a speaker. If, for instance, some one were to recite an alexandrine, an auditor in moving with the aforesaid velocity, starting at the moment when he heard the last foot of the line, would find successively the eleven other feet which had been uttered before, and would thus hear the alexandrine backwards. As to the theory itself, it suggests a curious reflection, that nature might have caused sound to travel, not at the rate of 340 metres a second, and that its velocity, which depends on the density and the elasticity of the air, might have been very much less. Why, for instance, might it not have been transmitted at the rate of only a few centimetres a second? Now see what would be the result if this were the case. Men would not be able to speak to one another when walking together. Let two friends be conversing, and suppose one takes a step or two in advance, or goes on, say the distance of a metre; now, if sound were to take many seconds to cross this metre, the consequence would be that, instead of hearing the phrases spoken in their right order by his friend, the foremost walker would hear in an inverse order the sounds conveying the anterior phrases. In that case we could not speak whilst walking, and three-fourths of mankind would not be able to hear one another. These remarks, my friend, induce me to suggest to you, in this connection, for your consideration, a subject well worthy of attention, and which has hitherto received little notice--that of the adaptation of the human organism to its terrestrial environment. The manner in which man sees, in which he hears; his sensations, his nervous system, his build, his weight, his density, his walk, his functions--in a word, all his actions are regulated and constituted by the condition of your planet. None of your acts are absolutely free and independent. Man is the obedient, though unconscious, creature of the organic forces of the Earth. [Sidenote: The human organism derived from the Earth.] [Sidenote: Organic life accords with its habitat on each planet.]