G. F. Becker — Kant as a Natural Philosopher. 103 



Kant appeals to his theory of Saturn as a confirmation of the 

 credibility of his whole hypothesis. Nevertheless he represents 

 the rings not as a relic of a condensing nebula but as an ema- 

 nation from the planet. The rings, according to his theory, are 

 composed of discrete particles* condensed from fumes and 

 vapors which had been thrown off from the equator of the 

 planet by rapid rotation while the planet was still in a highly 

 heated condition. These particles acquired their moment of 

 momentum from the planet and revolved in obedience to the 

 law that this moment is constant. He attempts to account for 

 the stability of the mass by its division into many rings, point- 

 ing out that if it were continuous, friction must destroy its 

 motion. 



Kant also computed the then unknown period of rotation of 

 Saturn on the hypothesis that centrifugal force and attraction 

 are equal at its surface, so that the rings are practically con- 

 tinuous with the planet. He obtained a period of 6 h 23 m 53 s . 

 Herschel in 1794 from direct observations found its period 

 10 h 16 m , which differs from Prof. A. Hall's determination by a 

 very few minutes. Mr. Faye supposes the German astron- 

 omers to have omitted mention of Kant's prediction out of 

 regard for the philosopher, the discrepancy between it and the 

 observations being " overwhelming." The French astronomer, 

 however, also remarks that the discrepancy, while calling for 

 explanation, does not invalidate the theory. Perhaps Kant's 

 theory of tidal retardation would have filled the gap. Kant 

 also speculated on the flattening of Saturn and concluded that 

 the density must increase towards the center of the planet. 

 This conclusion he extended to Jupiter and inferred its 

 applicability to other heavenly bodies. 



In the zodiacal light he saw an analogue to the Saturnian 

 rings, but he drew an essential distinction between the mate- 

 rials which reflects the zodiacal light and the rings of Saturn. 

 The velocity of rotation of the sun being quite insufficient to 

 maintain particles in free revolution near its surface, the heat 

 of the sun must cooperate to keep the fume-like mass in a state 

 of expansion even if the material came from the sun, as Kant 

 thought probable. He also contemplated the possibility that it 

 is a remnant of the nebula. 



simple cases, applicable to the question in hand, of the problem of three bodies 

 and generalized from the result. It seems impossible that he -should not have 

 perceived the true nature of the question, or that he snould have committed him- 

 self without an inquiry which was qualitatively satisfactory. 



* Kant reached this result independently, but afterwards became acquainted 

 with an investigation of Dominico Cassini's, Mem. de l'Acad., Paris, 1705, p. 14, 

 in which the rings of Saturn are regarded a^ swarms of minute satellites. This 

 is nearly but not quite Kant's view ; for his rings are, so to speak, raw material 

 of which the satellites might have been made, but were not. 



