80 Things not generally Known. 



Jupiter in . . 1712 years 



Saturn .... 3113 



Uranus . . . 6226 ,, 



Neptune . . . 9685 



If, thei'efore, a person had commenced his journey at the period of the 

 Christian era, he would now have to travel nearly 1300 years before he 

 would arrive at the planet Saturn ; more than 4300 years before he 

 would reach Uranus ; and no less than 7800 years before he could reach 

 the orbit of Neptune. 



Yet the light which comes to us from these remote confines of the 

 solar system first issued from the sun, and is then reflected from the 

 surface of the planet. When the telescope is turned towards Neptune, 

 the observer's eye sees the object by means of light that issued from 

 the sun eight hours before, and which since then has passed nearly 

 twice through that vast space which railway speed would require al- 

 most a century of centuries to accomplish. Bouvier's Familiar Agtro- 



GEAND RESULTS OF THE DISCOVERY OF JUPITER'S 

 SATELLITES. ' 



This discovery, one of the first fruits of the invention of the 

 telescope, and of Galileo's early and happy idea of directing its 

 newly-found powers to the examination of the heavens, forms 

 one of the most memorable epochs in the history of astronomy. 

 The first astronomical solution of the great problem of the 

 longitude, practically the most important for the interests of 

 mankind which has ever been brought under the dominion of 

 strict scientific principles, dates immediately from this disco- 

 very. The final and conclusive establishment of the Coperni- 

 can system of astronomy may also be considered as referable 

 to the discovery and study of this exquisite miniature system, 

 in which the laws of the planetary motions, as ascertained by 

 Kepler, and specially that which connects their periods and 

 distances, were specially traced, and found to be satisfactorily 

 maintained. And (as if to accumulate historical interest on 

 this point) it is to the observation of the eclipses of Jupiter's 

 satellites that we owe the grand discovery of the aberration of 

 light, and the consequent determination of the enormous velo- 

 city of that wonderful element 192,000 miles per second. Mr. 

 Dawes, in 1849, first noticed the existence of round, well-de- 

 fined, bright spots on the belts of Jupiter. They vary in situa- 

 tion and number, as many as ten having been seen on one 

 occasion. As the belts of Jupiter have been ascribed to tho 

 existence of currents analogous to our trade-winds, causing tho 

 body of Jupiter to be visible through his cloudy atmosphere, Sir 

 John Herschel conjectures that those bright spots may possibly 

 be insulated masses of clouds of local origin, similar to the 

 cumuli which sometimes cap ascending columns of vapour in 

 our atmosphere. 



It would require nearly 1300 globes of the size of our earth 



