THE INNER PLANETS. 97 



planet, nor is it likely that any further satellites 

 of Mars are in existence. 



The discovery of a zone of small planets in 

 the space between Mars and Jupiter belongs 

 completely to the nineteenth century, although 

 the existence of a planet in the vacant space 

 was suspected three centuries ago. In 1772 the 

 subject was taken up by Johann Elert Bode 

 (1747-1826), afterwards director of the Berlin 

 Observatory, who investigated a curious numer- 

 ical relationship, since known as Bode's Law, con- 

 necting the distances of the planets. If four is 

 added to each of the numbers 0, 3, 6, 12, 24, 

 48, 96, and 192, the resulting series represents 

 pretty accurately the distances of the planets 

 from, the Sun, thus 4 (Mercury), 7 (Venus), 

 10 (The Earth), 16 (Mars), 28, 52, (Jupiter), 

 and 100 (Saturn). After the discovery of 

 Uranus, in 1781, it was found that it filled up 

 the number 196. Bode, however, saw that 

 the number 28, between Mars and Jupiter, was 

 vacant, and predicted the discovery of the planet. 

 Aided by Franz Xavier von Zach (1754-1832), 

 he called a congress of astronomers, which as- 

 sembled in 1800 at Schroter's observatory at 

 Lilienthal, when, for the purpose of searching 

 for the missing planet, the zodiac was divided 

 into twenty-four zones, each of which was given 



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