1861.] on Bunsen and Kirchhoff's Spectrum Observations. 327 



1. The light emitted by luminous sodium vapour is homogeneous. 

 The sodium spectrum consists of one double bright yellow line. 



2. This briglit double sodium line is exactly coincident with 

 Fraunhofer's dark double line D. 



3. The spectrum of a Drummond's Light (like that of all incan- 

 descent solids) is continuous. It contains no dark lines or spaces. 



4. If between the prism and the Drummond's Light a soda flame 

 be placed, a dark double line identical with Fraunhofer's dark double 

 line D is produced. 



5. If instead of using Drummond's Light we pass sunlight through 

 the soda flame, we see that the line D becomes much more distinct 

 than when sunlight alone is employed. 



6. The sodium flame has, therefore, the power of absorbing the 

 same kind of rays as it emits. It is opaque for the yellow " D " rays. 



7. Hence we conclude that luminous sodium vapour in the sun's 

 atmosphere causes Fraunhofer's dark double line D. The light given 

 off from the sun's solid body producing a continuous spectrum. 



8. In a similar manner the presence in the solar atmosphere of 

 potassium, iron, magnesium, nickel, and chromium has been proved. 



Kirchhofifs own words may perhaps render this matter still more 

 plain. " The sun," says Kirchhoff", " consists of a glowing gaseous 

 atmosphere, surrounding a solid nucleus which possesses a still higher 

 temperature. If we could see the spectrum of the solar atmosphere 

 without that of the solid nucleus, we should notice in it the bright lines 

 which are characteristic of the metals it contains. The more intense 

 luminosity of the internal nucleus does not, however, permit the 

 spectrum of the solar atmosphere to become apparent ; it is reversed 

 according to my newly discovered proposition ; so that, instead of the 

 bright lines which the luminous atmosphere by itself would have 

 shown, dark ones appear. We do not see the spectrum of the solar 

 atmosphere itself, but a negative image of it. This case, however, 

 with an equal degree of certainty serves to detect the metals present in 

 the sun's atmosphere. All that we require for this purpose is a very 

 accurate knowledge of the solar spectrum, and of the spectra of the 

 individual metals." 



Kirchhoff" is at present engaged in continuing these observations ; 

 and although only eighteen months have elapsed since the first dis- 

 covery was made, he has already mapped more than seventy lines in 

 the solar spectrum, between D and E, which are produced by iron. 

 He has shown that the well-known group in the green, known as 6, is 

 caused by magnesium, whilst other coincident lines prove the presence 

 of nickel, chromium, potassium, and sodium in the solar atmosphere. 



The speaker regretted that he was unable to show even a drawing 

 of these coincident lines, as no representation of them has yet been 

 completed. 



The lines produced by many metals possessing very distinctly 

 marked spectra are seen to coincide with none of the dark solar lines ; 



