RECENT PROGRESS IN ASTRONOMICAL RESEARCH. 169 



interfere, the total range varies between two-thirds of a second, as a maximum, 

 to but a few hundredths of a second, generally speaking, as a minimum. 



In consequence of the variability of the coefficient of the annual term above 

 mentioned, the apparent average period between 1840 and 1855 approximated 

 to ;580 or 3!»0 days: widely fluctuated from 1855 to 1865; from 1SG5 to 1885 

 was very nearly 427 days with minor fluctuations; afterwards inci'eased to near 

 440 days. * * * 



Mr. Chandler expressed these results mathematically by an equation 

 in which the variation of latitude is given as the sum of two periodic 

 terms, and he found that this expression very closely represented all 

 the observations he had .so laboriou.sly collected. 



The valuable consequences of this discovery of Mr. Chandler's are 

 numerous. First of all, they showed why certain series of observa- 

 tions made with the most painstaking- care at the national observa- 

 tories of the United States, Great Britain, and Russia had exhibited 

 di.scordancies which had led to distrust of the very best pieces of 

 apparatus, and had involved laborious, co.stly, and fruitless eft'orts 

 to remove what now were found to be nonexisting defects. In some 

 instances even the reputation for accuracy of able astronomers had 

 been clouded by such inexjilicable discordancies in their work, which, 

 in the light of the new discovery, now prove only the evidences of the 

 faithfulness and accuracy of these observers. Again, as to the con- 

 stant of aberration, on which depends one important method of 

 determining the distance of the sun (that great astronomical quantity 

 on which all the conclusions as to the distances, ma.sses, and other 

 elements of the solar system hang, together with all the exact predic- 

 tions depending on solar theory), it proves that the determinations 

 of this imjjortant constant are sensibly affected by the variations of 

 latitude. 



Professor Turner, in his Astronomical Discovery, has the following 

 passage indicating still another possible etfect of the wandering of 

 the pole : 



If the axis of the earth is executing .small oscillations of this kind, there 

 should be an effect upon the tides; the liijuid ocean should feel the wobble of the 

 earth's axis In some way ; and an examination of the tidal registers showed 

 that there was. in fact, a distinct effect. It may cause some amusement when 

 I say that the rise and fall are only a few inches in any case, but they are 

 unmistakable evidences that the earth is not spinning smoothly, but has this 

 kind of unbalanced vibration, which I have compared to the vibrations felt by 

 passengers on an imperfectly engineered twin-screw steamer. A more sensa- 

 tional effect is that apparently earthiiuakes are more numerous at the time when 

 the vibration is greatest. We remarked that the vibration waxes and wanes, 

 much as that of the steamer waxes and wanes if the twin screws are not run- 

 ning quite together. Now, the passenger on the steamer would be prepared to 

 tind that breakages would be more numerous during the times of vigorous 

 oscillation, and it seems probable that in a similar way the little cracks of the 

 earth's skin, which we call great earthquakes, are more numerous when these 

 unbalanced vibi'ations are at their maximum ; that is to say, about once every 



