Thus in A the twist may be right-handed or left-handed; in B the polarity of a given end may become north or south; in C the circular magnetization may be clockwise or counter-clockwise; in D the length may be increased or diminished; in E the magnetization may become stronger or weaker.
Biot further ascertained that this rotation of the plane of polarization varies as the distance traversed in the plate and very nearly as the inverse square of the wave-length, and found that with certain specimens of quartz the rotation is in a clockwise or right-handed direction to an observer receiving the light, while in others it is in the opposite direction, and that equal plates of the rightand lefthand varieties neutralize one another's effects.
Most of the solar vortices indicate clockwise rotation in the southern hemisphere and counter-clockwise rotation in the northern, as in the case of terrestrial cyclones.
This, however, is not generally retained in one plane, and the spire projects, little by little, on the side which was originally left, but finally becomes right (in dextral forms, with a clockwise direction, if viewed from the side of the spire; but counter-clockwise in sinistral forms).
These residual forces tend to make the whole earth turn round the centre C in a clockwise direction.
The area of the cycle, viz., that enclosed by the path Bcda, represents the balance of external work done by the substance in one cycle, and is positive if the cycle is described clockwise 0' O as indicated by the arrows.
If we mark off a segment AB along the line of action so as to represent the force completely, the A moment is represented as to magni FIG 15 tude by twice the area of the triangle OAB, and the usual convention as, .o sign is that the area is to be reckoned positive or negative iccording as the letters 0, A, B, occur in counter-clockwise or clockwise order.