366

THE PLANET SATURN.

which it will be possible satisfactorily to observe the disap-pearance of the ring.

Certain further complications might arise in exceptionaloases; as, for instance, if the plane of the rings should pass, orvery nearly pass, through the Earth and the Sun at the samemoment; but such instances are so rare that we need notdiscuss them.

It will, however, be a very useful exercise for the reader towork out what will happen if he suppose the Earth to startfrom various positions in the circle of its orbit, at the instantwhen Saturn passes through c. We hope that the two caseswhich we have discussed may suffice to show how any othersmay be treated, and how simple the explanation of so appa-rently complicated a series of phenomena really is.

Those who desire fuller information may consult Mr. Proctor’swell-known work upon Saturn , in which he enters somewhatmore elaborately into calculations than in many of his morerecent astronomical treatises. He has there exhaustively dis-cussed the whole question.

Fora complete historical account of the successive discoveriesof the rings, of their divisions and many interesting peculiar-ities, we refer our readers to Grant’s “ History of PhysicalAstronomy.” We will only mention here a few of the prin-cipal episodes in the story. It is well known that Galileo Galilei wrote to Kepler in the year 1610, announcing adiscovery connected with the planet Saturn in the form of alogogriphe, as follows :—

“ smaismrmilmepoetaleumibunenugttauiras,”which Kepler supposed to refer to Mars , and to be intended torepresent the words :—

Salve umbistineum geminatum Martia proles! ”

“ Hail , twin companionship, children of Mars ! ”

In fact, Kepler imagined that Galileo had discovered twosatellites of Mars . But the real meaning intended was :—

“ Altissimum planetam tergeminum observavi.”

■“ I have observed the most distant of the planets to have a triple form.” *

* See the “ Sidereal Messenger of Galileo Galilei,” translated by Rev.E. S. Carlos, pp. 88 and DO.