528 Sir DAVID BREWSTER on the Lines of the Solar Spectrum, 



upon a continuous and uninterrupted spectrum of artificial white 

 light. The general scale of these delineations is four times great- 

 er than that of FRAUNHOFER, but some portions of them are 

 drawn on a scale twelve times greater, which became necessary 

 from the impossibility of representing in narrower limits the nu- 

 merous lines and bands which I have discovered. The length of 

 FRAUNHOFER'S spectrum is 15^ inches. Mine, upon the same 

 scale, is nearly 17 inches. The length of the general spectrum, 

 which I have delineated, is about five feet 8 inches, and the 

 length of a spectrum, corresponding to the scale on which I have 

 delineated parts of it, is seventeen feet. 



FRAUNHOFER has laid down in his map 354 lines, but in the 

 delineations which I have executed, the spectrum is divided into 

 more than 2000 visible and easily recognised portions, separated 

 from each other by lines more or less marked, according as we 

 use the simple solar spectrum, or the solar and gaseous spectrum 

 combined, or the gaseous spectrum itself, in which any breadth 

 can be given to the dark spaces. 



The suggestion of Mr TALBOT induced me to watch narrow- 

 ly the state of the defective solar lines at different seasons of the 

 year, in order to observe if any change took place in the combus- 

 tion by which the sun's light is generated, or in the solar atmos- 

 phere through which it must pass. Such changes I have found 

 to be very general in every species of terrestrial flame. The de- 

 finite yellow rays which exist in almost all white lights, flicker 

 with a variable lustre ; and analogous rays in the green and blue 

 spaces proceeding from the bottom of the flame, exhibit the same 

 inconstancy of illumination. In the course of the winter obser- 

 vations, I observed distinct lines and bands in the red and green 

 spaces, which at other times wholly disappeared ; but a diligent 

 comparison of these observations soon shewed, that these lines 

 and bands depended on the proximity of the sun to the horizon, 

 and were produced by the absorptive action of the earth's atmosphere. 

 I have no hesitation, therefore, in affirming, that, during the 



