Fig. 15.—Saturn, Jan. 26, 1889 (Antoniadi).
There is one important particular in which the belts of Saturn differ from those of Jupiter. Jupiter’s belts are straight, whereas Saturn’s are sensibly curved. Supposing, as is probable, that Saturn’s belts are parallel to the planet’s equator, then we must assume that the plane of this equator makes a rather considerable angle with the ecliptic. Spots on Saturn are very rare. Whether Saturn has an atmosphere seems uncertain, or perhaps it may be said that one has not been proved to exist but may exist. The question of polar snow is also uncertain, but Sir W. Herschel thought he could trace changes of hue at the poles which might be due to the melting of snow.
It is usual to speak of the planet itself under the name of the “Ball” when it is not a question of referring to the whole Saturnian system collectively. In consequence of its distance from the Sun, Saturn undergoes no equivalent to a phase; or to be more exact, no phase can be detected, though theoretically when the planet is in quadrature the disc must undergo an infinitesimally small loss of light.
Though the point has now-a-days no scientific importance, it may perhaps be desirable just to make a brief allusion to Sir W. Herschel’s curious theory that Saturn was seen by him to be compressed not only at the poles but at the equator, so that it resembled a parallelogram with the corners rounded off. It is difficult to imagine what could have given rise to this strange idea, though, of course, Herschel’s good faith in advancing it cannot be called in question. I refer to it because it will be found mentioned in so many books on astronomy, often under the name of the “square-shouldered” figure of Saturn. As a theory it may be regarded as quite exploded in consequence of accurate measures by Bessel, Main and others having conclusively shown that the form of the ball does not depart from that of a regular spheroid.
In referring to Saturn generally, we speak of its ring in the singular number, but, in point of fact, there are several rings—three in particular. The principal bright ring is really double, and within the innermost bright ring there is a dusky one, perfect as a ring, but not luminous as the outer rings are. By way of distinguishing one ring from another, it is usual to adopt Struve’s nomenclature, whereby the outermost bright ring is called A, the inner bright ring B, and the dusky ring C.
A good engraving will convey more fully and more clearly an idea of what the Saturnian system consists of than the fullest verbal description will do. (See Frontispiece.)
To the earliest astronomers who possessed telescopes, Saturn proved a great puzzle, because it seemed to undergo changes of shape which were quite inexplicable on any principles then known. Galileo, when first he saw it, thought it presented an oval outline which might be due to a central planet having a smaller planet on each side of it, and accordingly he announced to his friend, Kepler, that the most distant planet was tergeminum or tri-form. But greater magnifying power led him to arrive at the conclusion that the planet was not a triple combination of spheres, but one body, either oblong or oval in outline. This conclusion, however, was soon found to be untenable, because the two (supposed) tributary bodies gradually decreased in size until they entirely disappeared. Galileo writing to his friend, Welser, in December 1612, thus expressed himself:—
“What is to be said concerning so strange a metamorphosis? Are the two lesser stars consumed after the manner of the solar spots? Have they vanished or suddenly fled? Has Saturn, perhaps, devoured his own children? Or were the appearances indeed illusion or fraud, with which the glasses have so long deceived me, as well as many others to whom I have shewn them? Now, perhaps, is the time come to revive the well-nigh withered hopes of those who, guided by more profound contemplations, have discovered the fallacy of the new observations, and demonstrated the utter impossibility of their existence. I do not know what to say in a case so surprising, so unlooked for, and so novel. The shortness of the time, the unexpected nature of the event, the weakness of my understanding, and the fear of being mistaken have greatly confounded me.”
