698 THE POPULAR SCIENCE MONTHLY. 



parts, or the surplus of atomic movement which is not consumed by 

 its inner work. A high temperature means, therefore, a great excess 

 of such movement, which again is identical with a greater number of 

 momentary vibrations. In fact, the movement of light and the move- 

 ment of heat differ essentially by regularity {rhythmen), and greater 

 movement of heat passes, therefore, jiresumedly into movement of light, 

 if it has reached the lowest number of vibrations for light, namely, 

 those of red light. If, after a greater and greater rising of temj^era- 

 ture up to its highest possible degi-ee, the rapidity of movement in- 

 creases more and more, we observe, besides the red light, first, yellow 

 light, forming orange with the former; later, we meet also blue light, 

 which, however, in most cases, only serves to form white light wilh 

 the red and yellow, and which is only predominant in very rare cases, 

 as observed by Deville. Under ordinary circumstances, we only get 

 a yellow or red light containing more or less white. The more white 

 it contains the greater is, naturally, its eiFect of light ; and, as white 

 only appears at the highest temperatures, it becomes evident that the 

 temperature of a flame does not exert a secondary influence on its 

 luminosity, but is its principal factor. The second factor is the elimi- 

 nated carbon, the molecules of which radiate the light. The lumi- 

 nosity of two flames of the same temperature corresponds, therefore, 

 to the number of its carbon-molecules, and " luminosity in general 

 equal to the jjroduct of the radiating molecules and their tempera- 

 tures " for illuminating purposes, it may be presumed that the latter 

 should amount to at least 1,000. 



The above-mentioned phenomena of light may easily be observed 

 on solid bodies if heated. They are not observable on gases as long 

 as they expand unhindered. It would, however, be wrong to attrib- 

 ute this negative behavior to the circumstance alone that, by the un- 

 hindered expansion, the amount of the added or produced heat was 

 changed into power. This is contradicted by the high temperature 

 which, among others, the non-luminous exj)losive gas-flame {Knoll- 

 gas) possesses. Besides, it is also observed that platinum wire be- 

 comes incandescent in every possible non-luminous flame, even in a 

 flame produced by nitrogen on coal-gas, if the requisite temperature 

 to change heat into light is present. 



If we may conclude from this that the atoms of gases may be 

 brought into light-vibrations without becoming luminous, then we 

 possess bodies which conduct the light (the gases), and others which 

 radiate light (the solid bodies), just as we have conductors of elec- 

 tricity and idio-electrical bodies. 



An explanation of this diflerence is ofiered when light is considered 

 as atomic movement. Its efiect to the eye is then the product of 

 quantity and velocity. 



In a given space we find a much larger mimber of vibrating atoms 

 if filled with solid matter than if filled with gas. The waves of light 



