largely of the Sun’s own original rotation and travel therefore most nearly in its plane. And as a fact Mercury, the Benjamin, does differ from the others by revolving in a plane inclined some 7° to their mean, agreeing in this with the Sun’s own rotation, with whose plane it was probably originally coincident (digression from it now being due to secular retrogression of the planets’ nodes) [see NOTE 4]. From the relations which advance has left unchanged we pass to those phenomena which seemed to present congruities in Laplace’s day, but which have since proved void owing to subsequent detection of exceptions. Time prevents my making the catalogue complete, but the reader shall be shown enough to satisfy him of the problem’s complexity and to whet his desire for further research—on the part, preferably, of others. [Illustration: CHART SHOWING INCREASING TILTS OF THE MAJOR PLANETS.] First comes, then, the rotations of the planets upon their axes, which Laplace supposed to be all in the same direction, counter to the hands of a clock; for the heavens mark time oppositely from us. All those within and including Saturn, the only ones he knew, turn, indeed, in the same sense that they travel round the Sun. But Uranus departs from that direction by a right angle, wallowing rather than spinning in his orbit; while Neptune goes still farther in idiosyncratic departure and actually turns in the opposite direction. Here, then, Laplace’s congruity breaks down, but in its place a little attention will show that a new one has arisen. For Saturn’s tilt is 27° and Jupiter’s 3°, so that with the major planets there is revealed a systematic righting of the planetary axes from inversion through perpendicularity to directness as one proceeds inward toward the Sun. Another congruity supposed to exist a century ago was the exemplary agreement of all the satellites to follow in their planetary circuits the pattern set them by their primaries round the Sun. But as man has penetrated farther into space and photographic plates have come to be employed, satellites have been revealed which depart from this orderly arrangement. This is the case with the ninth, the outermost, satellite of Saturn and with the eighth, the outermost, of Jupiter. But, as before, the breaking down of one congruity seems but the establishing of another. It appears that only the most distant satellites are permitted such unconformity of demeanor. For departure from the supposed orthodoxy occurs in both instances where the distance is most, and does not occur in the case of all the other satellites found since Laplace’s day, eleven in number, nearer their planets.