fluorescence. A color-measuring apparatus commonly used in experiments in the 1900s was used in conjunction with partially silvered mirrors to split one beam of light into two beams. This resulted in two beams of light parallel to one another having the same intensity and color. The beams of light were projected onto a white background, creating patches of light that were squares. The white light was added to one of the patches of colored light, the patch on the right. A rod was inserted in the path of the two beams so that there would be no space in between the colored surfaces. An additional rod was used to create a shadow where the white light scattered onto the patch that was not to receive addition of white light (the patch on the left side). The amount of white light added was determined as one half of the luminosity of the colored light. The red light source, for example, had more white light added than the yellow light source. He began using two patches of red light, and in fact, the addition of white light to the light patch on the right caused a more yellow tone than the pure red light source. The same results happened when the experimental light source was orange. When the light source was green, the addition of white light caused the appearance of the patch to become yellow-green. Subsequently, when white light was added to yellow-green light, the patch of light appeared primarily yellow. In a mixture of blue-green light (with a slightly higher percentage of blue) with white light, the blue appeared to take on a reddish hue. In the case of a violet light source, the addition of white light caused the violet light to take on a blue tint. Abney hypothesized that the resulting change in hue that occurred was due to the red light and green light that were components of the white light being added. He also thought that the blue light that also comprises the white light beam was a negligible factor that had no effect on the apparent hue shift. Abney was able to prove his hypothesis experimentally by matching his experimental values of percentage composition and luminosities of red, green, and blue sensations to the calculated values almost exactly. He examined the percentage composition and luminosity found in the different spectral colors as well as the