Let us, in concluding the first part of our paper, at the risk of repetition, bring out in bolder relief a statement which presents the philosophy of all the various processes of the indigo vat, and at the same time, a conclusive argument for the use of this material, in preference to all cheaper substitutes. Indigo cannot enter into a fibre until it is dissolved. It cannot be dissolved so long as it is in a blue state. When reduced by any of the processes above described to the white state, it is easily dissolved, and can enter the pores of the fibre. Upon exposure to the oxygen of the air it takes up an equivalent of oxygen; it returns to the blue state, and, being then insoluble, it cannot be washed away from the fabric, and being saturated with oxygen it cannot be changed by air or light. This theory of the application of indigo involves a lesson to manufacturers, dealers, and consumers, especially of woollen fabrics. The theory, as well as experience, dating back to the dawn of the textile arts in the East, establishes that this material is incalculably superior to any other, in permanence at least, for imparting to woollen fibre a blue color, or as a foundation for most of the darker colors. By far the largest proportion of all cloths are of dark colors,—blue, black, green, brown, gray, or mixed,—and can advantageously receive in all or a portion of the fibre constituting them a direct dye or bottom for other dyes from indigo. It may be safely stated that, as a whole, no cloths in the world are manufactured from such good wool as those produced in the United States. We might expect that the shoddy goods of Yorkshire should be further falsified by fugacious dyes; but is it not a shame that our admirable wool should be deprived of half its value by parsimony in dyeing? The slightest shortcomings in dyeing are revealed in wear. The writer cannot forbear referring to an illustration directly before his eyes. He is wearing a garment, reduced now to the retired service of an office coat, made of an admirable cheviot cloth of American manufacture. The cloth originally was selected not only for its excellent texture, but as an illustration of philosophical principles applied in the formation of color. The tissue was made by weaving three yarns of distinct colors,—blue, yellow, and red. Either of those hues alone would have been glaring and conspicuous, but, by the law of color, the combination of blue, red, and yellow makes black, and the new cloth at a distance had the effect of a dark mixture. Upon exposure to ordinary wear, the yellow and red have retained their pristine hues; the blue, not being indigo dyed, has faded; and the original dark mixture, although sound in fabric, has become of a yellowish brown. The extra expense of a permanent dyeing material forms so small a proportion of the whole cost of a finished garment, that it ought not to be generally spared. The reform cannot be made by