Certain spots move faster than others, so that if we would obtain a fair value for the rotation period of any current it is not sufficient to derive it from one marking alone; we must follow a number of objects distributed in different longitudes along the current and deduce a mean from the whole."[10] [Footnote 10: The Observatory, No.

286, December, 1899.] Nor is this all.

Observation indicates that if we could look at a vertical section of Jupiter's atmosphere we should behold an equally remarkable contrast and conflict of motions.

There is evidence that some of the visible spots, or clouds, lie at a greater elevation than others, and it has been observed that the deeper ones move more rapidly.

This fact has led some observers to conclude that the deep-lying spots may be a part of the actual surface of the planet.