Note * — Chapter XI

The extraordinary appendages thus gradually revealed present a constantly varying aspect according to the seasons of the long Saturnian year. At Saturn's equinoxes they disappear, being turned edgewise; then, reappearing, they gradually broaden until at the solstice, 7⅓ years later, they are seen at their widest expansion; while from this point they narrow again to the following equinox, and repeat the same process with the opposite side of the ring illuminated, the whole set of changes being gone through in 29 years 167·2 days. Barnard's measures give for the outer diameter of the outer ring 172,310 miles; while the clear interval between the inner margin of the Crape Ring and the ball is about 5,800 miles, and the width of the great division in the ring-system (Cassini's) 2,270 miles. In sharp contrast to these enormous figures is the fact that the rings have no measurable thickness at all, and can only be estimated at not more than 50 miles. They disappear absolutely when seen edgewise; even the great Lick telescope lost them altogether for three days in October, 1891.*