Scientific American 38, 12.6.1847
In the solar rays the tints are so combined that in their transmission through the atmosphere they yield a perfectly colorless light. - These tints are red, yellow and blue, and to their exact balance are we indebted for pure light. In artificial light this equilibrium is destroyed, for the red and yellow tints prede minute, and we are therefore more unable to judge of color by candle light. To remedy this it has been suggested to employ cobalt in the manufacture of lamp globes, &c., so that a slight tinge of blue might correct the artificial light.