282 POPULAR SCIENCE MONTHLY 



How was the order of the universe understood by the ancients; 

 for instance, by Pythagoras, Plato or Aristotle? It was either an 

 immutable type fixed once for all, or an ideal to which the world 

 sought to approach. Kepler himself still thought thus when, for 

 instance, he sought whether the distances of the planets from the sun 

 had not some relation to the five regular polyhedrons. This idea 

 contained nothing absurd, but it was sterile, since nature is not so 

 made. Newton has shown us that a law is only a necessary relation 

 between the present state of the world and its immediately subsequent 

 state. All the other laws since discovered are nothing else; they are 

 in sum, differential equations; but it is astronomy which furnished 

 the first model for them, without which we should doubtless long 

 have erred. 



Astronomy has also taught us to set at naught appearances. The 

 day Copernicus proved that what was thought the most stable was 

 in motion, that what was thought moving was fixed, he showed us 

 how deceptive could be the infantile reasonings which spring directly 

 from the immediate data of our senses. True, his ideas did not 

 easily triumph, but since this triumph there is no longer a prejudice 

 so inveterate that we can not shake it off. How can we estimate the 

 value of the new weapon thus won? 



The ancients thought everything was made for man, and this il- 

 lusion must be very tenacious, since it must ever be combated. Yet 

 it is necessary to divest oneself of it ; or else one will be only an eternal 

 myope, incapable of seeing the truth. To comprehend nature one 

 must be able to get out of self, so to speak, and to contemplate her 

 from many different points of view; otherwise we never shall know 

 more than one side. Now, to get out of self is what he who refers 

 everything to himself can not do. Who delivered us from this illusion ? 

 It was those who showed us that the earth is only one of the smallest 

 planets of the solar system, and that the solar system itself is only 

 an imperceptible point in the infinite spaces of the stellar universe. 



At the same time astronomy taught us not to be afraid of big 

 numbers. This was needful, not only for knowing the heavens, but to 

 know the earth itself; and was not sO easy as it seems to us to-day. 

 Let us try to go back and picture to ourselves what a Greek would 

 have thought if told that red light vibrates four hundred millions 

 of millions of times per second. Without any doubt, such an assertion 

 would have appeared to him pure madness, and he never would have 

 lowered himself to test it. To-day an hypothesis will no longer 

 appear absurd to us because it obliges us to imagine objects much 

 larger or smaller than those our senses are capable of showing us, 

 and we no longer comprehend those scruples which arrested our pre- 

 decessors and prevented them from discovering certain truths simply 



