4 3 THE POPULAR SCIENCE MONTHLY. 



scene of a constant precipitation of meteoric matter from the inside of 

 the ring-system. 



Now, there is one important peculiarity which distinguishes the 

 equatorial bright zone of Saturn from that of Jupiter. Jupiter's axis 

 is almost square to the level of the path in which he travels around 

 the sun ; so that his equatorial zone lies nearly in that level, and is 

 therefore directly illuminated by the sun. The aspect of Jupiter in 

 fact, as seen from the sun, is always that which our earth presents in 

 spring and autumn. But Saturn has an axis very considerably sloped 

 to the level of the path in which he travels. It is more sloped even 

 than our earth's axis. So that in the course of his long year of 10,759 

 days (29^ of our years) Saturn's globe presents toward the sun all the 

 varying aspects which our earth presents, only with a somewhat greater 

 range of variation. At one time he is placed as our earth is in spring, 

 and then his equatorial belt, as seen from the sun, appears to lie straight 

 across the middle of his disk. Rather more than seven years later he 

 is posed as our earth is posed at midsummer, his northern pole is 

 bowed toward the sun, and his equator is seen as a half-oval, curving 

 far south of the middle point of his disk. He passes on from this po- 

 sition, and in seven more years he is placed as our earth is in autumn, 

 with his equator again lying straight across his disk. Then, seven years 

 or so later, he presents the aspect of our earth at midwinter, his equa- 

 tor curved into a half-oval passing far to the north of the middle point 

 of his disk. And, finally, at the end of yet seven years more (or, more 

 exactly, of one complete Saturnian year from the commencement of 

 these changes), he is again as at first. Now, it seems manifest that, if 

 the great cloud-zone which surrounds Saturn, appearing as a nearly 

 white ring, were due to solar action, it would fluctuate in position as 

 these changes proceeded. The very length of the Saturnian year 

 should insure the occurrence of such fluctuations. We have only to 

 inquire what takes place on our own earth, where, though we have 

 nothing comparable with the belt systems of Jupiter and Saturn, we 

 have, nevertheless, over ocean-regions, a sun-raised tropical cloud-band 

 in the middle of the day. This cloud-band follows the sun, being equa- 

 torial in spring, passing far north of the equator, even to the very limit 

 of the torrid zone, in summer, returning to the equator in autumn, 

 passing to the southern limit of the torrid zone in winter, and returning 

 again to the equator in spring. In fact, this cloud-band as seen from 

 the sun would always cross the middle of the earth's face as a straight 

 line in spring and autumn, and as considerably more than a half-oval, 

 agreeing in position with the tropics of Cancer and Capricorn, at mid- 

 summer and midwinter. But nothing of the sort happens in Saturn's 

 case. His equatorial w T hite ring is really equatorial at all times, in- 

 stead of being drawn to his tropics at his midsummer and midwinter 

 seasons. This, in our opinion, is decisive of the origin of this great 

 band. If it were sun-raised, it would obey the sun ; but, being raised 



