979 



Chase.] ^*^ [April 21. 



rants and towards retarded rotation in the other two, the sum of the ac- 

 celerating being exactly equal to the sum of the retarding tendencies. No 

 evidence has ever been adduced of any actual lagging of the water to 

 maintain the normal position of the tidal crests relatively to the moon. 

 There are many reasons for believing that the apparent westward motion, 

 with a mean equatorial velocity of 1000 miles an hour, is only a motion of 

 form, maintained by the combined influences of intermolecular elasticity, 

 atomic elasticity or quasi-elasticity, variations of pressure on account of 

 varying attraction, and such wave propagation as may be needed for the 

 adjustment of opposite meridional and horizontal, static and dynamic ten- 

 dencies. The adjustment maybe brought about, as I have shown in Xotc 

 317, without any frictional diminution of the speed of rotation. 



219. The, Moon and the Chief Planetary Belt. 



The importance of Earth's position, at the centre of the belt of greatest 

 condensation, is further shown by the harmonic reactions between the 

 Jupiter-Saturnian belt and Earth, with its satellite. The shortening of 

 rotation-period which would represent a nebular contraction of Sun from 

 Jupiter's to Earth's mean locus, corresponds to the shortening which 

 would represent a contraction from Moon's semi-axis major to Laplace's 

 terrestrial limit ; the ratio between Moon's synodic and sidereal periods 

 corresponds to the ratio between the locus of Saturn's incipient subsidence 

 (secular aphelion) and axis-major. The time of rotation, in an expanding 

 or contracting nebula, varies inversely as the square of radius : 



^p. -^ ^y^ =, 5.20282 ^ 27.06912. 



Sidereal month -4- day ■= 27.32166. 



Synodic -^ sidereal month = 1.08087. 



Satvirn's sec. aph. -r- mean* = 1.08433. 



220. StalUity of Rotation- Periods. 



The relations of stellar rotation to oscillations which are propagated 

 with the velocity of light, the relations of primary planetary rotation to 

 planetary revolution, the relations of molecular rotation to electric, mag- 

 netic and tidal phenomena, the constancy of tendencies to harmonic oscil- 

 lation, the confirmation of nebular theories which is afforded by the 

 foregoing note, and the principle that no change in the vis viva of a 

 system can take place without foreign action, all indicate a stability 

 of rotation which is inconsistent with the hypothesis of tidal friction. 

 Moreover, the closeness of accordance between the mean daily thermal 

 and hygrometric adjustments of elasticity and the tidal variations of at- 

 mospheric pressure {Proc. Am. Ph. Soc., ix, 2S4-6, 391-3, S46-S), an ac- 

 cordance which is also shown in the lunar-monthly barometric tides (lb., 

 395-0; Proe. Roy. Soc. xiii, 329-33), furnishes additional grounds for be- 

 lieving that rotation is only modified revolution, that its period is deter- 



* According to Stocliwcl!. 



