In 1663 the Brothers Ball discovered that the rings are divided into two, or, at any rate, that a broad black stripe, such as is shown in fig. 30, separates the outer portion of the ring from the inner. Two years later these observers saw the stripe on the northern side of the rings, when the rings had so shifted in position that observers saw their southern side. Dominic Cassini recognised a corresponding stripe on the southern side. This was regarded as proving that there is a real division between the rings. The width of the gap thus separating the outside of the inner ring from the inside of the outer cannot be less than 1,600 miles. Cassini also detected another Saturnian moon in October, 1671, and, later, he discovered three others, making five Saturnian moons in all. Sir W. Herschel observed the rings with great care. He confirmed the discovery of the great division between the rings; but rejected the idea which was beginning to be entertained in his time, that there are many divisions. He found reasons for suspecting, but never actually proved, that the outer ring turns round in about 10½ hours. He also detected two small moons close to the outer ring. One other moon, detected independently by Bond at the Harvard Observatory, Cambridge, U.S., and by Lassell in this country in 1848, completes the set of eight moons now known to revolve around the planet Saturn. We need not here say much more about these moons, saving, perhaps, to note that the span of the entire Saturnian system of moons amounts to about 4,400,000 miles, nearly double that of the Jovian system. This is the largest system of satellites known to us. It is wonderful to reflect, when we look at the dull, slow-moving Saturn, that not only is the planet itself 700 times larger than the earth, not only is it girdled about by a ring system having a span exceeding more than 20 times the diameter of this earth on which we live, but that the entire span of the system over which that distant planet rules exceeds more than eighteen-fold the distance separating our earth from the moon. Return we now, however, to the consideration of the Saturnian ring-system. In 1850 a singular discovery was made. It was found by Bond, in America, and, a few days later, independently, by Dawes, in England, that inside the inner bright ring there is a dark ring almost as wide as the outer bright ring. One of the strangest circumstances about this inner ring is that where it crosses Saturn's disc the outline of the planet can be distinctly traced _through_ the dark ring, which is thus, in a sense, a semi-transparent body. I say "in a sense," because it does not follow that it really consists of semi-transparent matter any more than it follows from our being able to see through a gauze veil that the individual threads forming the gauze are made of a semi-transparent material.