32 THE RADIATIONS OF IGNITED BODIES. [MEMOIR I. 



Thus was discovered one of the fundamental facts in 

 spectrum analysis, a fact that has become of the highest 

 importance in astronomy, as furnishing a means for de- 

 termining the physical condition of the heavenly bodies, 

 and a test for the nebular hypothesis. An ignited solid 

 will give a continuous spectrum, or one devoid of fixed 

 lines; an ignited gas will give a discontinuous spectrum, 

 one broken up by lines or bands or spaces. 



About twenty years subsequently to this discovery, 

 Mr. Huggins (1864) made an examination of a nebula 

 in the constellation of Draco. It proved to be gaseous. 

 Subsequently, of sixty nebulae examined, nineteen gave 

 discontinuous or gaseous spectra, the remainder contin- 

 uous ones. 



It may therefore be admitted that physical evidence 

 has through this means been obtained demonstrating the 



o o 



existence of vast masses of matter in a gaseous condition, 

 and at a temperature of incandescence. The nebular hy- 

 pothesis of Laplace and Herschel has thus a firm basis.) 

 The strip of platinum was now placed in the position 

 . n **., Hi? f the slit which had 



J]a**tt given the spectrum rep- 

 resented at 1, and its 



temperature was raised 



2. 



7 o by the passage of a vol- 



j taic current. Though the 



= j metal could be distinctly 



- 1 2130 seen by the naked eye 



Fig. 4. when the temperature 



Spectra of dnylight and of incandescent platinum had 1'Cached about 1000 

 at different temperature, 



in passing the prism and telescope was so great that it 

 was necessary to carry the temperature to 1210 before 

 a satisfactory observation could be made. At this de- 

 gree the spectrum extended from the position of the fixed 



