of the arm as at E, and the determination of its resistance is made by altering the weight D until a certain definite speed of rotation is attained. It is evident that, knowing the length of the arm, the diameter of the axle on which the cord is wound, and the weight employed, the calculation of the resistance is a matter of simple arithmetic.
Fig. 140. The resistance of the body under investigation only forms part of the total resistance, and a preliminary experiment is necessary to determine the Resistance proper to the apparatus itself. Precautions were usually taken to prevent so far as possible frictional resistance, the variations of which would otherwise give rise to error of sensible magnitude.
§ 222. Early Investigations. Hutton—Vince.—One of the objects on which considerable experimental attention was focussed at an early period was the investigation of the solid
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