Excerpt from Cases Illustrative of Different Forms of Color-Blindness: Case I, Congenital Color Blindness; Case II, Tobacco Color-Blindness; Case III, Traumatic Color Blindness; A Clinical Lecture Delivered Before the Senior Class at the Jefferson Medical College, Philadelphia, April 5, 1895
Now, we will see if we can approach this subject in some way so that you will get a clear idea of the color sense and of the relations of colors. Here, on this plate I Show you a colored representation of what is commonly known as a ‘spectrum or solar spec trum. This teaches you that if you go into a dark room and make a small hole in a shutter, that the beam of light (or if passed through a prism) will break up into this arrangement of colors upon a screen, with blue light at one end and red light at the other, as everybody knows. The reason why the Spectrum is formed is because a beam of whitelight is made up of a number of rays having different wave lengths, or rates of vibrations. Thus, the red rays at one end of the spectrum have about four hundred million mil lions of vibrations per second, while the violet at the other end have over seven hundred and fifty million millions. All rays under four hundred billions of vibrations per second are not perceptible as light and are known as heat rays, while those higher than the violet can not be appreciated by the human eye and are only recognized by their chemic and physical effects. Between these extremes of red and violet are found the orange, yellow, green and blue rays with rates of vibration of four to eight billions per second.
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