September 4, 1914] 



SCIENCE 



337 



garding the distribution of animals although 

 some errors could be pointed out. The bio- 

 logic evidence can, however, all be interpreted 

 by other hypotheses than that of a polar pen- 

 dulation. 



The previous discussion has been given to 

 show the vague and warped evidence upon 

 which a system of terrestrial mechanics has 

 been raised. But this is really not the way 

 to test the hypotheses. They must stand or 

 fall by the astronomical and mathematical 

 implications. What then is the astronomic 

 evidence ? 



Euler long since pointed out that in a rigid 

 spheroid, if the axis of rotation did not exactly 

 coincide with the axis of figure, the former 

 would revolve around the latter. For the 

 earth, if absolutely rigid, this revolution of 

 the pole would be completed in 305 days. In 

 1890 Chandler showed that there was such a 

 motion, but that the period was about 428 

 days. In 1892 Newcomb showed that the dis- 

 crepancy between the calculated and the ob- 

 served period was owing to the fact that the 

 earth was not absolutely rigid. The difference 

 in the period implied an elasticity of the 

 earth's body comparable to steel, but did not 

 show plasticity. The motions are confined 

 within a circle about fifty feet in diameter. 

 The actual path is not, however, a circle, and 

 Chandler later showed that it was composed of 

 two harmonic terms, the one about 430 days, 

 the other 365 days. The former is the motion 

 previously described, and is called the Eulerian 

 nutation; the latter is regarded as due to sea- 

 sonal changes in precipitation and in the sea- 

 sonal shifting of atmospheric and oceanic 

 currents. There is no suggestion of a third 

 component of polar motion represented by a 

 progressive shifting in one direction. Such a 

 motion even if a fraction of a foot per year 

 would have become evident owing to the length 

 of the time over which refined latitude obser- 

 vations have been made. How does this ob- 

 served fixity of the axis compare with the de- 

 mands of the hypotheses of polar migration? 



A movement of as much as 10° since the 

 late Pleistocene, would apparently be at a 

 much faster rate than the previous migra- 



tions. Overlooking, however, this anomaly of 

 changing rate, suppose the time to be as long 

 as 200,000 years. This great length of time 

 would minimize the annual rate, giving a 

 movement of 18 feet per year. If the move- 

 ment of the pole is reduced to 3°, as suggested 

 by Eeibisch in a later work mentioned by Sim- 

 roth, this would be at an annual rate of 5.5 

 feet per year. The absence of even a small 

 fraction of this motion within the period of 

 precise astronomic observations would require 

 the added supposition that progressive migra- 

 tion for some unknown reason had greatly 

 slowed down or that pendulation was at its 

 turning point. The astronomic evidence lends, 

 therefore, no support whatever to the doctrine 

 of a wandering pole. 



Apparently Simroth thinks that the move- 

 ment of precession involves a motion of the 

 earth's axis within its body in a circle of more 

 than 20° radius (pp. 534-536). This, accord- 

 ing to him, is combined with the pendulation 

 movement, the result being that the path of 

 the pole is like the projected thread of a screw 

 of which the axis is the meridian 10° E. In 

 following out this idea under the title of the 

 "Probable True Path of Pendulation" he 

 naively says: 



Possibly there speaks already in favor of a mo- 

 tion of the north pole in a screw line instead of a 

 circle the uncertain statements of the handbooks. 

 One reads now of 25,000, now of 28,000 years. I 

 am not able to judge whence the different figures 

 come. Do they not lie perhaps in the insecurity of 

 the calculated elements which have been considered 

 as circular arcs while they are in truth part of a 

 screw line? 



The final test of polar migration lies, how- 

 ever, in the mathematical analysis of the ter- 

 restrial motions. Mathematical astronomers 

 have in general been opposed to the idea of a 

 changing axis of rotation, the permanent fix- 

 ity of the axis having been asserted by La- 

 Place and many others since his day. This 

 problem has been investigated further by Lord 

 Kelvin, but, as previously stated, more espe- 

 cially by G. H. Darwin. The work of these 

 men has been cited as offering no objection to 

 a Iftrge or even indefinite wandering of the 



