370 PHYSIOGRAPHY. [chap. 



and comparing them with the lines which are produced by 

 the combustion of various terrestrial elements, the presence or 

 absence of such elements in the sun may be inferred. For 

 the examination of the spectrum, special instruments, called 

 spectroscopes, are employed ; and the method of research 

 itself, which was suggested and worked out by Profs. Bunsen 

 and Kirchhoff, is known as spectrum analysis. 



By means of spectrum analysis, it has been found that the 

 sun contains a large number of elements, including hydrogen, 

 sodium, lithium, calcium, barium, magnesium, zinc, iron, 

 manganese, nickel, cobalt, chromium, titanium, aluminium, 

 and copper. Quite recently Dr. Draper, of New York, has 

 announced the discovery of oxygen, and probably also of 

 nitrogen in the sun.^ 



From the surface of the sun, enormous quantities of light 

 and heat are continually being radiated, or thrown out into 

 space, in all directions. The earth, however, on account 

 of its small size and its great distance, can receive but 

 an extremely small proportion of the total amount which is 

 thus shed. In fact, it is calculated, that our globe receives 

 less than the two-thousand-millionth part of the total quantity 

 of the sun's light and heat. All teriestrial phenomena, 

 which depend upon solar light and heat, are therefore effected 

 by means of this extremely minute fraction of the sun's stores 

 of energy. 



The sun is not only the principal source of heat and 

 light to our earth, but it is the centre of attraction by which 

 the revolving globe is maintained in its regular orbit. If 

 a piece of iron be held in front of a powerful magnet, it 

 will rush to the magnet, although there is no visible bond 

 between them. If the same piece of iron be left unsup- 



^ For a detailed account of the constitution of the sun see Contri- 

 hitioHs to Solar PtiysiiS. By J. Norman Lockyer, F.R.S. 1874. 



