210 FROM NEBULA TO NEBULA 



marks were caused by a toothed wheel rolled round the 

 ridge, or in any way, indeed, save the right one. 



Now, astronomical observations, especially in cases 

 of such super-delicacy as required in this case, cannot be 

 made at any hour of the day or night, but only at the most 

 propitious time of all midnight. That is to say, the 

 marks or "indentations" are registered twenty-four 

 hours apart just as Foucault's pendulum 's dents were 

 spaced by a second or so. A record being kept of these 

 latitude observations would speak only for themselves, 

 but would give no hint as to what occured between their 

 makings. Now, astronomers have mistakenly assumed 

 out of hand that the condition between times is the same, 

 or virtually the same, as at the moments when the ob- 

 servations are made in other words, they see the dents 

 in the act of being made in the circular ridge of sand, 

 but they do not see, or allow for, the vibrations of the 

 pendulum in between; they recognize the existence of 

 the long-period variations, but remain blind to the even 

 more significant diurnal ones. 



We have only to suppose that the earth, besides its 

 ordinary diurnal revolution, wabbles once around on its 

 true axis during each day, and from day to day, in a 

 rhythmical manner, with only the lengths of the ampli- 

 tudes varying seasonally and monthly according to the 

 changing positions of the sun and moon, to which lat- 

 ter we naturally turn for the dynamical explanation. 

 Thus may we combine consistently the actuality of daily 

 oscillations with Chandler's long periods of a year and 

 430 days respectively. These oscillations, be it observed, 

 are not simple rocking motions, back and forth like a 

 pendulum (which would not harmonize the phenomena), 

 but a rotatory motion, which the term wabbling aptly de- 

 scribes. The conditions require that when A is on the 

 meridian of midnight with a latitude plus, B at its mid- 

 night, twelve hours later, must show a latitude by the 

 same amount minus. A wabble of a period of twenty- 

 four hours, cooperating with the diurnal rotation, sup- 

 plies this requirement. Were it possible to make accurate 



