electric conductivity in the two directions and that the direction of maximum conductivity is also the direction of maximum absorption. Electric vibrations perpendicular to the direction of maximum conductivity are thus alone transmitted, the emergent beam being thus completely polarised (p. 75).
8. The Production of a "Dark Cross"
The interposition of a circular structure like that of a disc of rolled paper on the path of polarised electric radiation is found to project a dark cross into space, the outline of which can be definitely found by means of the exploring detector. The production of a dark cross can also be demonstrated by woody stems with concentric rings as also by ringed concretion of flint round a central nodule. Stalactite also gives similar results (p. 115).
9. Rotation of Plane of Polarisation
Right handed and left handed rotations of the plane of polarisation are produced by oppositely twisted jute elements. The electro-optic analogues of two varieties of sugar, dextrose and levulose, were thus obtained. An apparently inactive variety was produced by a mixture of equal numbers of positive and negative elements (p. 109).
B. The Characteristics of Metallic-contact Receivers
The systematic study of effect of electric waves on contact-resistance of various metals and metalloids showed certain characteristic differences.
