They are recorded by a special arrangement outside the cylinder, so that it is immaterial whether the liquid under test is transparent or not. Since the inner surface of the cylinder and the surface of the ball are exactly finished, the dimensions b and r can and must be established with the greatest accuracy likewise must be known the stroke of the ball and the time for travelling this stroke. (3) C is the constant inherent to the instrument, which can easily be verified by experiment with a fluid whose absolute viscosity is known. For a wide range of velocities U, the ratiois constant, while excessive e and very small velocities (not in consideration and not applied) cause an increase of the ratio R P U Inserting U = T, where H is the stroke of the ball, and T the corresponding time, gives RT w = L, where C = 15732Hcß. The pressure on the rear of the ball is supposed constant, caused by eddies arising in this part of the space. (2)* where e = b r r, b is the inner radius of the cylinder, and r is the radius of the ball. When the ball is moving coaxially in the cylinder where the fluid is held in rest by diaphragms sufficiently remote from the ball, the resistance is R = 6ap. I£, however, the ball is moving in a circular cylinder, provided a suitable clearance, sufficiently small velocities even with any considerable resistance R are available. System.) The demand of an infinite mass of fluid, and, further, the condition that the product Ur shall be negligible against the kinematic viscosity, equivalent to a very small R, detract from the value of the method. (I) gives the possibility of determining the coefficient g of absolute viscosity when the resistance, R, the velocity, U, and the radius, r, of the ball are known. AMONG the various devices for examining the absolute viscosity of fluids, the method based on the movement of a ball in a fluid mass of infinite dimensions has the most simple aspect.
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