In the interior of the cylinder is placed a kind of ventilator, Fig. 105. This consists of eight wooden wings, pierced with holes, and motion is communicated to it by means of the wheel, _b_, connected by the cord to the larger windlass. The wings of the machine when set in motion, strike incessantly in the cream, and so powerfully that the whole mass is agitated, and in this manner the separation of the butter particles is soon effected. The motion is so rapid that it is often necessary to turn the crank very slowly, especially just as the butter is coming. [Illustration: Fig. 105.] [Illustration: Fig. 106.] VALK’S HAND BUTTER-MILL, Fig. 106, has many advantages. It is less fatiguing to work than the old-fashioned churn, and even than Fürst’s, because the motion of the body required is simple and less exacting. And again, the churn takes up less room, and is easily transported, which is an important consideration in churning, on account of the influence of the temperature. In summer the heat may delay, or render the operation difficult, and in winter the coldness presents obstacles. A transportable churn can be moved into a cool place in summer, and a warm one in winter, when it is desirable. The dasher of the churn is also seen separate in the same figure. [Illustration: Fig. 107.] THE DOG-POWER CHURN, Fig. 107, economizes labor, while, at the same time, more butter is obtained, on account of the uniformity of the agitation produced. It is in use in all the Dutch provinces. The form and size of the churn are comparatively indifferent; but the tread-wheel and direction of the moving power are the important points. The diameter of the wheel is from ten to twelve feet, and the rim or outer circumference is made of boards two feet wide. The weight of the animal turns the wheel and moves the dasher by means of cogs, as shown in the figure. Where there is a sufficient supply of moving power, a churn with two dashers is sometimes attached, as shown in Fig. 108, in which case one dasher moves down while the other is raised. [Illustration: Fig. 108.] A large and strong dog is required, and he is easily taught to keep to his work, by beginning with short trials, and gradually lengthening them. A steady and uniform step is necessary, and this will soon be acquired. The dog is sometimes left free, and sometimes tied by a line. [Illustration: Fig. 109.] [Illustration: Fig. 110.]