against the centrifugal force of an appropriately arranged weight, which varies in like ratio. By this means the measurement of the reaction is made virtually independent of the velocity of flight, so that a possible source of error is avoided and the conduct of experiments is greatly simplified.
The Dines apparatus is illustrated in the form of a rudimentary diagram in Fig. 141, in which A is an arm of the whirling table pivoted at and revolving about the point B, a bell crank lever C D, delicately centred at E, carries on its two arms respectively the pressure plane, F (or other body whose resistance it is desired to ascertain), and the bob weight G whose centrifugal force forms the measure of the pressure reaction. The condition of equilibrium is that the resultant of the two forces passes through the pivot centre E. It is evident that these two forces, in equilibrium at any one speed, will be in equilibrium for all speeds, for their relative direction undergoes no change, and they are each proportional to the velocity squared and so are proportional to one another. The bob weight D is made adjustable on the arm D and the condition of equilibrium is ascertained by trial. In one modification the instrument is made to perform automatically its own adjustment.
§ 224. — Dines' Method (Mathematical Expression).
| Let, | area of plane.
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| „ | velocity of the bob weight.
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| „ | velocity of the centre of pressure of the plane.
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| „ | radius of the path of the weight.
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| „ | resistance (poundals) acting on the plane.
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| „ | centrifugal force of the bob weight (poundals).
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| „ | lever ratio, so that
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| „ | mass of bob weight.
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| „ | pressure on plane (poundals per square foot.)
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| „ | constant in expression, (§ 134).
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