Jupiter is exceptionally rapid. If the great planet required as much time for one of his rotations as does Mars, or the earth, then the new satellite of Jupiter would present the same anomalous feature to its primary as we actually find in Mars and its inner satellite.
There are so many mysteries about Jupiter that we are specially glad to welcome the new satellite in the hope that somehow it will afford a clue to their explanation. We are still ignorant of the true nature of the great red spot which has a period of rotation different from that of the planet itself. Then there are the small black spots which appear to revolve round the planet in a few minutes less time than the planet itself requires for its revolution. Professor Barnard's discovery is one of those achievements which is often succeeded by others of the same class. This has, indeed, been the case. The Fifth Satellite has been followed by a Sixth and a Seventh which have been detected by Photography. Professor Perrine, at the Lick Observatory, has the high honour to have added to our knowledge of the Solar system by the detection of these delicate objects.
