The cones, about the size of a small walnut, bear spirally arranged imbricated scales which subtend the three-angled winged seeds.
We conclude that a double line cannot be fairly resolved unless its components subtend an angle exceeding that subtended by the wave-length of light at a distance equal to the horizontal aperture.
If 1 2 and 1 1 be the thicknesses traversed by the extreme rays, and a denote the width of the emergent beam, the dispersion is given by 0 Sµ 0 2 - 11)/a, or, if t i be negligible, 0 = Sµt/a (6) The condition of resolution of a double line whose components subtend an angle 0 is that 0 must exceed X/a.
The latter view receives support from abnormal cones in which carpellary scales subtend axillary shoots, of which the first two leaves (fig.
Each of the twenty triangular faces subtend at the centre the same angle as is subtended by four whole and six half faces of the Platonic icosahedron; in other words, the solid is determined by the twenty planes which can be drawn through the vertices of the three faces contiguous to any face of a Platonic icosahedron.