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Published online by Cambridge University Press: 14 March 2018
Take three axes of reference OX, OY, OZ mutually at right angles. A convention must be made as to the positive direction of rotation about any line, and that usually adopted is as follows. A positive rotation about OX rotates OY towards OZ, one about OY rotates OZ towards OX, and one about OZ rotates OX towards OY. To find the positive direction of rotation for any line ON we must suppose ON moved to coincide with one of the axes, say OZ, and then apply the preceding rule.