DISCOVERY BY MEANS OF INFERENCE. 587 



that those distances appeared to agree with a particular 

 mathematical law ; and, having found that the distance 

 between Mars and Jupiter was twice as great as it should be 

 according to that law, inferred the existence of a missing 

 planet in that space, and this was soon afterwards proved 

 to be true by the discovery of the Asteroids. 1 It was by 

 means of observation and inference that Wilson, in 1774, 

 discovered the cavernous character of the spots on the sun. 

 By studying the positions and movements of the stars, Sir 

 William Herschel, in 1783, inductively inferred that the 

 entire solar system is travelling through space, straight 

 towards a point in the constellation Hercules. In the 

 year 1793, he also inferred and suggested that the spots 

 on the sun were openings in bright luminous solar clouds, 

 and that the seemingly black portions were parts of the 

 body of the sun itself. Schiaparelli, in 1862, by observing 

 that a comet crossed the orbit of the earth at the same 

 point as the shower of August meteorites, inferred that the 

 meteors travel in the same path as the comets. He also 

 tested that inference by calculation, and found it correct. 



From suitable data, it has been inferred that the 

 Earth is the largest dense solid of the solar planets ; that 

 Jupiter is probably composed chiefly of water and watery 

 vapour, with some solid nucleus. 2 As there is but a little 

 appearance of water or air upon the moon, the conclusion 

 has been inferred that there exists no vegetable or animal 

 life on that globe. From certain data, it has also been 

 calculated that the cold of space is about ninety degrees 

 below zero. 3 



By studying the fact that the eclipses of Jupiter's 

 moons rarely happened at exactly the calculated moment, 



1 See page 488. 



2 See Whewell, Plurality of Worlds, pp. 181-219. 



3 rind. p. 18J . 



