The Earth and its Early History 



There is an instrument called the spectroscope which 

 is used to break up or analyse light, and by its means 

 we can compare the quality of light from one source 

 with that from another. When looking through a 

 spectroscope we see a band of colour, red, orange, 

 yellow, green, blue, and violet, as in the case of the 

 rainbow. Now, if the source of the light is the Sun, 

 there will be a number of black lines running across the 

 band of light, and these lines have been proved to 

 belong to the spectra of different metals and gases, such 

 as Iron, Sodium, Hydrogen, and Helium, so that we 

 know that these substances are present in the Sun. 



In the same manner, by examining the light of a 

 star, we can find out a number of the elements of which 

 the body is made up, and many stars have been shown 

 to have a similar composition to the Sun. 



The Sun is therefore but one of the countless 

 thousands of stars which, separated from one another by 

 hundreds, if not thousands, of light-years, 1 go to make 

 up the visible Universe. 



The second class of bodies referred to above, the 

 nebulae, are, as their name suggests, cloud-like masses, 

 and they are faintly luminous. They cannot be seen by 

 the unassisted vision, but when viewed through a 

 telescope are found to be of two main classes, one 

 having a more or less spiral arrangement, and the other 

 being quite irregular in form. 



These bodies are of great interest to us, as it is 

 almost certain that the planets, including, of course, the 



1 A "light year" is the distance which light travels in a year and is the 

 unit employed for measuring stellar distances. It is 186,000 x 60 x 60 x 24 x 

 365 = 55865,696,000,000 miles. 



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