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 operation absurd, but it is the same in principle as the results produced in the attempt to form a spectrum by the combination of three primary pigments, reel, yellow and blue, because so produced the orange, green and violet, show by disk analysis from 54 to 80 per cent of black and white and are therefore as much broken as the corresponding colors in the papers of the broken scales, but not exactly the same in tone.

Those papers which are termed "Engine Colored Papers" are so named from the process of manufacture as distinguished from "coated papers" which comprise the first three sections of the book. In coated papers a white paper is covered with a coating of colored pigment "fixed" with a small amount of white gum, gelatine or glue, and in this way the pure color of the pigment is obtained. In the engine colored papers the color is mixed with the paper pulp in the process of making the paper. In a paper mill the tab or vat in which the pulp is kept stirred up and perfectly mixed is called the engine, and hence this technical term has been applied to such papers as are colored in the pulp. In this class of papers both sides are alike, and for this reason in some of the folding exercises these papers are preferred, also because they are thinner and tougher. Heretofore, it has been impossible to obtain engine colored papers in "families" or scales, but in this assortment the numbers from one to six, furnish six scales of three tones each, comprising the normal tones with tints and shades. Following these from seven to sixteen are a collection of unclassified colors including grays which are much used. All these can be analyzed and classified by the color wheel. Black and white complete this class. It is impossible to make any close approximation to a black in this class of papers, as when they are compared with the coated blacks the result is a very gray black, or very dark gray. All the colors in these papers from No. 1 A to No. 13 are quite light broken spectrum colors, but less broken than the coated papers designated as broken spectrum colors.