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110 it is not their lightness but their make-up that prevents from lying uneasy the head that wears this crown.

The mechanical marvel was not appreciated by early astronomers, who took it for granted that they were what they seemed, solid, flat rings, all of a piece. Even Laplace considered it sufficient to divide them up concentrically to insure stability. To Edouard Roche of Montpellier, as retiringly modest as he was penetratingly profound, is due the mathematical detection that to subsist they must be composed of discrete particles,—brickbats, Clerk Maxwell called them, when, later, unaware of Roche's work, he proved independently the same thing in his essay on Saturn's rings. Peirce, too, in ignorance of Roche, had half taken the same step a little before, showing that they must at least be fluid. Then in 1895 Keeler ingeniously photographed the spectrum of both ball and rings to the revealing of velocities in the line of sight of the different portions of the spectrum exactly agreeing with the values mechanics demanded.

The rings have usually been considered to be flat. At the time of their disappearance, however, knots have been seen upon them. It is as if their filament had suddenly been strung with beads. At the last occurrence of the sort in 1907, these beads were particularly well seen at several observatories, and were critically studied at Flagstaff. In connection with a