16 The Outline of Science 



scope < which we shall refer to immediately) has helped us so 

 much. It is to this wonderful instrument that we owe our know- 

 ledge of the composition of the sun and stars, as we shall see. 



'That the spectroscope will detect the millionth of a milli- 

 gram of matter, and on that account has discovered new ele- 

 ments, commands our admiration; but when we find in 

 addition that it will detect the nature of forms of matter 

 trillions of miles away, and moreover, that it will measure 

 the velocities with which these forms of matter are moving 

 with an absurdly small per cent, of possible error, we can 

 easily acquiesce in the statement that it is the greatest instru- 

 ment ever devised by the brain and hand of man." 



Such are some of the questions with which modern astron- 

 omy deals. To answer them requires the employment of instru- 

 ments of almost incredible refinement and exactitude and also the 

 full resources of mathematical genius. Whether astronomy be 

 judged from the point of view of the phenomena studied, the vast 

 masses, the immense distances, the aeons of time, or whether it be 

 judged as a monument of human ingenuity, patience, and the 



-t type of genius, it is certainly one of the grandest, as it is 

 also one of the oldest, of the sciences. 



The Solar System 



In the Solar System we include all those bodies dependent 

 on the sun which circulate round it at various distances, deriving 

 their light and heat from the sun the planets and their moons, 

 certain comets and a multitude of meteors: in other words, all 

 bodies whose movements in space are determined by the gravita- 

 tional pull of the sun. 



The Sun 



Thanks to our wonderful modern instruments and the 

 ingenious methods used by astronomers, we have to-day a re- 

 markable knowledge of the sun. 



