48 THE POPULAR SCIENCE MONTHLY. 



stop in its flight ; but the feeblest outward influence would be felt, 

 throwing it either into the sphere of attraction of our sun or into that 

 of Alpha Centauri. 



This sun called Centaurus is located in the southern sky, near the 

 antarctic pole. It appears to us in the form of a bright star of the 

 first magnitude. The sun nearest to us, next after this, is situated in 

 the northern sky, in the constellation Cygnus, or the Swan. It is 

 famous as 61 Cygni. Its distance is 400,000 times the radius of the 

 earth's orbit, or about fifteen trillions of leagues. I have often observed 

 this star : it is just visible to the naked eye, but to the telescope it is 

 double, as the preceding, only its components do not move around 

 each other, a conclusion which has much surprised me, although ar- 

 rived at by comparing all the observations made during the last hun- 

 dred years ; its mass, therefore, cannot be determined. But, however 

 that may be, the fact which should impress us is that the distances 

 which separate the suns of the universe are reckoned not by millions, 

 nor by billions, but by trillions of leagues. 



The most brilliant star of our sky, Sirius, is a sun whose volume, 

 judging from its light, should be 2,600 times larger than that of our 

 sun. Its distance is about 897,000 times thirty-seven millions, that is 

 about thirty-three trillions of leagues. 



Let us mention again among " our neighbors " the sixty-second of 

 Ophiuchus, situated near the equator. I have calculated that it weighs 

 about three times as much as our sun, that is, 900,000 times more 

 than the earth. Its distance is 1,400,000 times the semi-diameter of 

 the earth's orbit, that is, fifty-four trillions of leagues. 



Astronomers, since the time of Kepler, agree in admitting that 

 each of the countless suns that fill infinite space is the centre of a sys- 

 tem analogous to the planetary system of which we form a part. 

 Each of these suns that we see in the sky shows to us a luminous fire- 

 side around which other human families are gathered. Our eyes are 

 too feeble to see these unknown planets. The most, powerful of our 

 telescopes do not yet reach down to these depths. But Nature con- 

 cerns itself neither with our eyes nor with our telescopes, and so, be- 

 yond the boundaries that stop the flight of our tired conceptions, she 

 continues to display her boundless and magnificent works. 



However, the hour has come when these planetary systems different 

 from ours cease to slumber in the domain of hypothesis. In spite of 

 the telescope, celestial mechanics have already revealed the existence 

 of obscure stars, invisible in the rays of these distant suns, but which 

 affect them in their proper movements across immensity ; and already 

 powerful telescopes have contemporaneously recognized several among 

 the stars known before to exist only in hypothesis. 



One of the most splendid conquests of sidereal astronomy has been 

 the discovery of the system of Sirius, made some fifteen years since. 

 For a long time, from careful measures of its position, it has been 



