If wholly of wool, they are now swaddled carefully in an outer cloth, and sprinkled with water, and laid upon a warm plate of metal which sends the steam up through the hat which is to be pressed, and slightly rubbed, sprinkled again, and turned over. Continuing the pressing and rubbing, and by repeating these operations for some time, the motions are transmitted to all the inclosed fibres of wool with an irritating feeling, as it were, exciting their propensity for travelling, till the outer hairs, in their motions, warp themselves with each other and the surface appears skin-like and becomes smooth. During these actions, the hat inside of the cloth must be several times changed in position and kept in proper form, when its swaddling envelope and the paper within which kept the inside open and free may be removed. These operations concluded, the tender hat must now be subjected to a much more laborious operation, where, properly speaking, the grand practical art of felting takes place, where thousands of thousands of filaments are all in active though slow motion, all travelling on their own individual course, independent of, and at the same time dependent upon, each other for their mutual support, being carefully guided collectively, by the hatter's good judgment. This stage of the operation is a wet one requiring an open boiler surrounded by planks, which slope towards the centre, called a battery, Fig. 4, suitable for six or eight men to work at. Each man is provided with a rolling-pin, cloths, brushes, &c. The soft and tender hat is laid upon one of these planks or benches, wrapped in a damp cloth, and carefully wetted, squeezed, folded, rolled and unrolled, keeping it constantly moistened by dipping it in the hot water of the boiler, folding and unfolding with every variety of crossings, rolling it as a scroll, pressing, shaking, dipping and rolling it again and again, the hatter all the while bending over his work in front of the almost boiling caldron, and surrounded by steam. He labors hard, ever changing the position of the hat under his hands, so as to make it an evenly felted and perfect piece of work, which these oft-repeated motions ultimately accomplish. [Illustration: Fig. 4. Battery for Sizing Hats.] This is the grand felting operation; the cause of which was so long considered a mystery, and now ascertained to result from the peculiar natural construction of the animal fibre, as already explained.