204 Kansas Academy of Science. 



that a large portion of the data which have been utilized in the 

 present researches on the latitude were derived by methods which 

 dispense with levels, or with circles, a part of them indeed with 

 both, and yet that the results of all are harmonious. On the con- 

 trary, let us admit, although merely for argument's sake, that all 

 the known means of determining the direction of gravity are sub- 

 ject to a common law of periodical error which vitiates the result 

 of astronomical observation, obtained by whatever methods, and in 

 precisely the same manner. Now, the observed law of latitude 

 variation includes two terms, one a period of fourteen months, <and 

 the other of twelve. Since the phases of the first term are repeated 

 at intervals of two months in successive years, and hence in a se- 

 ries of years come into all possible relations to conditions of tem- 

 perature dependent on season, the argument against the reality of 

 the fourteen months' term absolutely fails." 



Heretofore the observations made by astronomers in Europe and 

 America, in all of which there was some puzzling error, were im- 

 mediately rectified when Mr. Chandler applied his new rule to 

 them. The constant of aberration has been wonderfully improved, 

 but there is room yet to secure greater accuracy. 



Again, if the axis of the earth is making small oscillations of 

 this kind, there should be an effect upon the tides. The ocean 

 should feel the swinging motion of the earth's axis in some way. 

 The tidal registers show that there is a distinct effect. The rise and 

 fall of the tide are only a few inches, but they are evidences of an 

 irresistible character that the earth is turning around in an unbal- 

 anced vibration. The vibration at one time is waxing and at an- 

 other waning. 



In conclusion, it may be said that in the consideration of this 

 subject we find that when Bradley, 160 years ago, began to work 

 out the problem of parallax, he was led to the discovery of the 

 "aberration of light," and finding that an uncertain element per- 

 sisted in presenting itself at every turn of his work, he was led to 

 the discovery of the nutation of the earth's axis. But even at this 

 point he found another diSiculty remaining over. Death cut short 

 the work of the great astronomer. Twenty years ago the work was 

 resumed by an American. Now it is an accepted fact that not only 

 does the earth's axis spin around, according to the theory of nuta- 

 tion, but there is another and stronger motion of the earth's axis, 

 and that is, that there is an actual change of the position of the 

 earth's axis in the earth itself, causing the latitude of the earth to 

 change at every point on its surface. 



