658 THE POPULAR SCIENCE MONTHLY. 



ous spectrum uninterrupted by lines is produced, when the light 

 emanating from solid and liquid incandescent bodies is passed through 

 a prism. 2. A spectrum interrupted by bright lines is produced when 

 the light emanates from flames or ignited vapors and gases. 3. A 

 spectrum interrupted by dark lines is produced, when light emanating 

 from a source giving a continuous spectrum, is passed through gaseous 

 or vaporous matter giving spectra of the second order. 



Now, it has been found that, when various elements are volatil- 

 ized in the flame of a lamp, the light gives a spectrum interrupted 

 by bright lines whose character and position are different for different 

 elements. It has also been discovered that the dark lines of spectra 

 of the third order correspond precisely in position with the bright 

 lines in spectra of the second order : they thus indicate the existence 

 of elements which are volatilized in the ignited vapors or gases. The 

 coincidence of position of these bright and dark lines was first ob- 

 served and described by Foucault, of Paris, in 1849; but their real 

 significance was first indicated in 1859, by Kirchhoff, of Heidelberg. 

 These delicate lines carry across the immeasurable abysses of the ce- 

 lestial spaces evidences of their origin ! 



The numerous lines of the spectrum are separated from one another 

 the fan of light is opened out its entire pattern is brought distinct- 

 ly under view and all of its minute details are revealed by trans- 

 mitting the light through a succession of prisms : this constitutes the 

 Spectroscope. (This was illustrated by a diagram.) 



By means of the spectroscope, no less than fourteen terrestrial ele- 

 ments have been identified as existing in the sun's atmosphere. Mr. 

 Willian Huggins and Prof. W. A. Miller, by ingenious modifications 

 of this instrument, have been able to extend spectrum analysis to more 

 than sixty of the brighter fixed stars. Like our sun, they give spectra 

 with dark lines ; thus indicating that the stars (as the sun) must have 

 intensely heated solid or liquid nuclei, surrounded by ignited gaseous 

 atmospheres. 



Encouraged by his success with the fixed stars, Mr. William Hug- 

 gins applied the potent method of spectrum analysis to the examina- 

 tion of the nebula?. He was rewarded by a most important discovery 

 in relation to the physical constitution of these wonderful objects. On 

 the 29th of August, 1864, he applied his spectroscope to a planetary 

 nebula in Draco. He was astonished to find that there was no appear- 

 ance of a band of colored light, such as a star would give ; but, in 

 place of this, there were three isolated bright lines on a dark ground 

 a true gaseous or vaporous spectrum. In other words, the object was 

 not a cluster of stars, but a true nebula. Mr. Huggins was not slow in 

 following up this line of investigation. During the two years succeed- 

 ing his first observation, he examined the spectra of more than sixty 

 nebulae and clusters. Of this number, about twenty gave spectra 

 with bright lines ; that is, were gaseous bodies. The remaining forty 



