Astronomy and Terrestrial Physics. 165 



determinations at both places, and the observations therefore 

 made at times differing by twelve hours. The inevitable infer- 

 ence is that the changes observed are not in the position of the 

 celestial pole, but in that of the zenith ; in short, that the phe- 

 nomenon is not one of nutation, strictly speaking, but rather a 

 change in the position of the terrestrial pole, affecting the geo- 

 graphical latitude of the point of observation. 



In Nos. 248-251 of the Astronomical Journal are a series of 

 articles by Dr. S. C. Chandler, giving the result of his later in- 

 vestigations of this periodical valuation. In 1884, '85 he had 

 made a series of determinations of the latitude of Cambridge, 

 with his then newly invented instrument, the Almucantar. 

 These showed a curious progression in the values obtained for the 

 latitude, to which he called attention in the Astronomische Nach- 

 richten as early as May, 1885. A continuation of the observa- 

 tions confirmed the phenomenon, and a new discussion of the 

 whole, with this fuller material, has given almost identical results ; 

 and showed both a maximum and a minimum, as well as a period 

 of about fourteen months. The further discussion of this, and 

 various other series of observations in which similar unexplained 

 anomalies had been found, led him to the general result that the 

 earth's axis of figure is revolving around that of rotation, from 

 west to east in a period of 427 days ; so that one pole revolves 

 about the other in a circle, the radius of which is about thirty 

 feet. 



After discussing various series of observations suitable for the 

 purpose, Chandler has arrived at the conclusion that the adoption 

 of this hypothesis affords the true solution of various discord- 

 ances which have long perplexed astronomers. Incidentally he 

 points out, as a probable result of the incorporation of this new 

 anomaly in the latitude, that the value of the constant of aberra- 

 tion, now commonly employed in preference to Struve's, is likely 

 to prove too large ; and that Struve's value is nearer the truth. 

 By a comparative discussion of simultaneous observations made 

 at Melbourne, Leyden, Pulkowa and Washington, he demon- 

 strates that the phenomenon is not simply local or regional, but 

 is terrestrial. He furthermore shows that Bradley's zenith-sector 

 observations, which originally led to the discovery of aberration 

 and nutation, also reveal the effect of the periodic latitude-varia- 

 tion with remarkable distinctness, and finds that these, as also 

 various other series, indicate that the period has, in general, been 

 lengthening since the last century. But he infers that, so far as 

 can be recognized at present, the lengthening of the period has 

 not proceeded according to any regular law, but appears to a cer- 

 tain extent capricious ; and moreover that there is some relation 

 between the amplitude and the period of the variation. 



In No. 251 of the same Journal Prof. Newcomb points out that 

 the 427-day period is perfectly consistent with dynamic laws, 

 since we may suppose the deviation from Euler's theoretic value 

 to be due to imperfect rigidity of the earth and to the fluidity of 



