RECENT PROGRESS IN ASTRONOMICAL RESEARCH. 



171 



of arc, which can be transhited into feet or meters by remembering 

 that one second of arc at the j^ole is about 100 feet, or 30 meters, so 

 that the diameter of the larger curves is about 40 feet, or 12 meters. 

 The time is indicated in years and tenths of a year by the figures 

 adjoining the curves themselves. Thus, beginning with 1899.9 the 

 curve passes over the years 1900, 1901, etc., and ends at 1906.0. It 

 is plainly shown by this irregular curve what an apparently lawless 



- •t-0."lO 



+0."10 0."00 -0."10 



Movement of eartli's axis, 1X99 to 1906. 



-0."20 



wobble of the earth's axis is produced by the joint action of two 

 periodic factors, one of about 4;')7 days and one annual, the first of 

 constant and the second of varial)le amplitude. Since 1890 it has 

 be^'U found that five of the long ])ei"iods are almost exactly equal to 

 six of the shorter, so that the whole movement nearly repeats itself 

 every six years. It is interesting, though not conclusive, to note that 

 the severe earthquakes of 1900 occurred soon after the time of maxi- 

 nuim activity of the pole, which accords with the hypothesis touched 

 upon by Professor Turner, as already cited. 



