Compare with this description Fig. 91, which shows some of the appearances presented by the ring at different positions of Saturn in its orbit. It was their varying aspects that led Huyghens to insert the last words of his description, for, if the plane of the ring coincided with the plane of the earth's orbit, then at all times the ring must be turned edgewise toward the earth, as shown in the middle picture of the group. Fig. 92 shows the sun and the orbit of the earth placed near the center of Saturn's orbit, across whose circumference are ruled some oblique lines representing the plane of the ring, the right end always tilted up, no matter where the planet is in its orbit. It is evident that an observer upon the earth will see the _N_ side of the ring when the planet is at _N_ and the _S_ side when it is at _S_, as is shown in the first and third pictures of Fig. 91, while midway between these positions the edge of the ring will be presented to the earth. [Illustration: FIG. 92.--Aspects of the ring in their relation to Saturn's orbital motion.] The last occasion of this kind was in October, 1891, and with the large telescope of the Washburn Observatory the writer at that time saw Saturn without a trace of a ring surrounding it. The ring is so thin that it disappears altogether when turned edgewise. The names of the zodiacal constellations are inserted in Fig. 92 in their proper direction from the sun, and from these we learn that the ring will disappear, or be exceedingly narrow, whenever Saturn is in the constellation Pisces or near the boundary line between Leo and Virgo. It will be broad and show its northern side when Saturn is in Scorpius or Sagittarius, and its southern face when the planet is in Gemini. What will be its appearance in 1907 at the date marked in the figure? 143. NATURE OF THE RING.--It is apparent from Figs. 91 and 93 that Saturn's ring is really made up of two or more rings lying one inside of the other and completely separated by a dark space which, though narrow, is as clean and sharp as if cut with a knife. Also, the inner edge of the ring fades off into an obscure border called the _dusky ring_ or _crape ring_. This requires a pretty good telescope to show it, as may be inferred from the fact that it escaped notice for more than two centuries during which the planet was assiduously studied with telescopes, and was discovered at the Harvard College Observatory as recently as 1850.