definite in direction, [178];

name, [180];

width of, [179], [180], [182];

length of, [183];

visible by virtue of length, [181];

oddities of, [183];

number of, [184];

systematic arrangement of, [184], [185], [187-191], [248];

connect with polar caps, [325], [339], [373];

import of system of, [338], [372], [373];