Page:Popular Science Monthly Volume 7.djvu/718

698 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 movement of heat differ essentially by regularity (rhythmen), and greater movement of heat passes, therefore, presumedly 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 temperature up to its highest possible degree, the rapidity of movement increases 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 with 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 effect 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 eliminated carbon, the molecules of which radiate the light. The luminosity of two flames of the same temperature corresponds, therefore, to the number of its carbon-molecules, and "luminosity in general equal to the product of the radiating molecules and their temperatures" 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 attribute this negative behavior to the circumstance alone that, by the unhindered 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 explosive gas-flame (Knall-gas) possesses. Besides, it is also observed that platinum wire becomes 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 electricity and idio-electrical bodies.

An explanation of this difference is offered when light is considered as atomic movement. Its effect to the eye is then the product of quantity and velocity.

In a given space we find a much larger number of vibrating atoms if filled with solid matter than if filled with gas. The waves of light