THE PLANET MARS.

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cellence, and to possess remarkably good defining power.Indeed, both in America and in England the two satelliteswere much better seen in 1879 than had been anticipated;the reason perhaps being, that in practice it is always easierto see a faint body when we know where to look for it, thanto discover it for the first time when our gaze is roamingabout in a somewhat vagrant way over the field of view.They have again been visible, but only for a few days,during the Opposition of 1881. We can hardly, however,hope that they will be seen any more before the year 1888,possibly not until 1890.

To these two satellites, the smallest by far of all the knownmembers of the Solar System (with the exception, perhaps, ofsome of the numerous family of minor planets), the names ofDeimos and Phobos have been assigned. These names havebeen variously rendered Dread and Terror, or Fear and Flight ,or Dread and Fear . They are to be found in a passage in thefifteenth book of the Iliad, in which Homer uses them todescribe the two companions of Ares, or Mars , from which, atthe suggestion of Mr. Madan, they were adopted for thesatellites. In Pope ’s translation we read :—

“ With that he gives command to Fear and FlightTo join his rapid coursers for the fight.

Then, grim in arms, with hasty vengeance flies;

Arms that reflect a radiance through the skies.’'

These two minute attendants of their primary are so smallthat it is impossible to measure any appreciable diameters oftheir discs, or to judge of their sizes, except by estimating ascarefully as may be the amount of light which they reflect.This has been done with every possible precaution byProfessor Pickering (see vol. xi., Annals of Harvard CollegeObservatory); and it lias been concluded by him, and by someother observers, upon the assumption of their light-reflectingpower being similar to that of Mars itself, that their diametersmost probablj’ lie between six and seven miles. There seemsto be little, if any, doubt that Phobos , the inner one, is thebrighter of the two; especially when due allowance is madefor its nearer proximity to the glare of the planet in the field of