______________________________________________________________________ | | | | | | | | Electricity | Coal-Gas | Acetylene | | | |________________|__________________|_______________|_______| | Colour | | | | | | | | | in | | | | | | With | | | Spectrum.| Arc. | Incan- | Lumin- | Incan- | Alone.| 3 per | Sun- | | | | descent.| ous. | descent.| | Cent. | light.| | | | | | | | Air. | | |__________|______|_________|________|_________|_______|_______|_______| | | | | | | | | | | Red | 2.09 | 1.48 | 4.07 | 0.37 | 1.83 | 1.03 | 1 | | Yellow | 1.00 | 1.00 | 1.00 | 0.90 | 1.02 | 1.02 | 1 | | Green | 0.99 | 0.62 | 0.47 | 4.30 | 0.76 | 0.71 | 1 | | Blue | 0.87 | 0.91 | 1.27 | 0.74 | 1.94 | 1.46 | 1 | | Violet | 1.08 | 0.17 | 0.15 | 0.83 | 1.07 | 1.07 | 1 | | Ultra- | | | | | | | | | Violet | 1.21 | ... | ... | ... | ... | ... | 1 | |__________|______|_________|________|_________|_______|_______|_______| These figures lack something in explicitness; but they indicate the greater uniformity of the acetylene light in its proportion of rays of different wave-lengths. It does not possess the high proportion of green of the Welsbach flame, or the high proportion of red of the luminous gas- flame. It is interesting to note the large amount of blue and violet light in the acetylene flame, for these are the colours which are chiefly concerned in photography; and it is to their prominence that acetylene has been found to be so very actinic. It is also interesting to note that an addition of air to acetylene tends to make the light even more like that of the sun by reducing the proportion of red and blue rays to nearer the normal figure. H. Erdmann has made somewhat similar calculation, comparing the light of acetylene with that of the Hefner (amyl acetate) lamp, and with coal-gas consumed in an Argand and an incandescent burner. Consecutively taking the radiation of the acetylene flame as unity for each of the spectrum colours, his results are: