268 Dr. S. Tolver Preston on Certain Questions 



solar tidal-action* would, however, tend to be outweighed by 

 the relative proximity of our planet to the sun ; since the 

 tide-generating-force of one body on another is inversely as 

 the cube of the distance between them. 



But if the Nebular Hypothesis should demand retrograde 

 rotation primordially, and since or.r globe's rotation is now 

 direct (with only 23° inclination to its orbit about) ; then an 

 almost complete reversal must have occurred, or the terrestrial 

 pole must have been (inferentiall y ) twisted through some- 

 thing like 157° by tidal-action of the sun during the 

 demonstrably great epoch of time lapsed in the past. If this 

 be so, or the reasoning be regarded as having weight, then it 

 appears that the geological evidence of the former prevalence 

 of a tropical kind of vegetation within the polar circle, w T ith 

 glacial scenery in Southern Europe, need no longer perplex 

 observers. For, consistently with the inverting of the earth's 

 axis, the terrestrial pole must for a lengthy epoch have been 

 directed towards the sun (lying in proximity to the plane of 

 the ecliptic), — resulting naturally in a temporary inversion 



* Since the effect of tidal-action depends on the time available, and 

 varies inversely as the cube of the intervening distance, and since the 

 Nebular Hypothesis requires that the birth of the planet Jupiter and. 

 that of our earth should be separated by the lengthy time-epoch de- 

 manded for evolution in two intervening planetary zones ; it seems that 

 its greater proximity to the sun has not fully succeeded in compensating 

 for the curtailed time-interval available for the influence of solar tidal- 

 action in the case of our globe. So that while the spinning axis of the 

 planet Jupiter has suffered a nearly complete reversal, or the plane of its 

 axial rotation has been brought practically into parallelism with the plane 

 of its orbital revolution, our earth's axis is still removed about 28° from 

 this position. 



In respect to the part played by friction in deviating the rotation-axis 

 in each case, we may observe that rotating-earth and spinning-top are 

 comparable. 



A top spinning, with (let us say) axis inclined 28° to the vertical, is, 

 by the pull of gravity, caused to " precess "; while in the case of the earth, 

 the excess pull of solar gravitation upon the equatorial protuberance next 

 the sun, entails the precessional movement (as we know). 



The inner periphery of the inclined toe [of the top in rapid rotation] 

 strives, by its frictional grip, to hurry on the slower precessional 

 movement. Then, in accord with the familiar property of the axis of a 

 spinning body to deviate in a direciion at right angles to the force applied, 

 this acceleration of the precessional movement causes the axis of the top 

 to rise to the vertical, in opposition to gravity. 



So in the instance of our earth, while friction [here, of the tidal belt] 

 tends to check its axial spin, the friction goes to assist the precessional 

 movement of our globe ; which accordingly, in an analogous manner, will 

 cause the terrestrial axis to rise into a vertical position in relation to the 

 ecliptic-plane, or ultimately to set itself perpendicular to the plane of the 

 terrestrial orbit, which then becomes coincident with that of the revo- 

 lution of the tidal belt. 



