VARIATION OF LATITUDE.' 



By J. K. Rees. 



The question is frequently asked, "How can latitude change'?" 

 There are two ways, obviously. First, we may imagine that a portion 

 of the earth slips on the surface of the globe, due, say, to earthquake 

 shock. Then if the movement of the mass has been toward the 

 equator the latitude of that place is decreased; if toward the pole of 

 the earth the latitude is increased. But suppose that some forces at 

 work on the earth cause it to revolve about a new axis, then we 

 have at once a new equator, and the latitudes of all points on the 

 earth's surface change except at those places where the old and new 

 equator iutersect. 



If, for example, the earth's axis of revolution should be changed so 

 as to pass through this hall, the latitude would be chauged from a 

 little over 40°, as it now is, to 90°. There are changes no doubt pro- 

 duced by the slipping of portions of the earth's strata, but we know 

 that these causes are insiguificant and local. The only way that lati- 

 tudes could be made to change throughout the world would be by 

 changes in the axis of rotation of the earth, thus changing tbe position 

 of the equator. 



Are there any undisputed evidences of a variation in the latitude of 

 a place, and is it large? 



To day the evidence is overwhelming, but the amount is small; so 

 small, in fact, that only the refined instruments of the present day 

 have been able to discover it; though now, that it is discovered, older 

 observations show it. 



Laplace, in his Mecanique Celeste (Tome V, p. 22), says : "All astron- 

 omy depends ujion the invariability of the earth's axis of rotation and 

 upon the uniformity of this rotation." 



He considered that down to the beginning of this century astrom- 

 ical instruments had not been able to show any variation of latitudes. 



' From a lecture before the New York Academy of Sciences, April 29, 1895. Printed 

 in Science, new series. Vol. I, No. 21. 



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