SHIFTING OF THE EARTH'S AXIS 421 



values of the latitude be plotted along a vertical line and time along 

 the horizontal, we shall obtain the representation of a simple harmonic 

 motion, the crest of the wave corresponding to a maximum value of 

 the latitude and the trough of the wave to the minimum value. 



About the time of the expedition to Honolulu, Dr. Seth C. Chandler, 

 of Cambridge, Mass., one of America's foremost astronomers, took up 

 the subject of the variation of latitude and through a brilliant series of 



. 



Fig. 3. 



researches, published in the Astronomical Journal, succeeded in setting 

 forth a number of very interesting results. Dr. Chandler examined 

 all the astronomical observations made with transit instruments, 

 meridian circles, zenith tubes and allied forms of instruments, which 

 were at all suitable for throwing light upon the subject. The first and 

 most interesting result obtained by Dr. Chandler was that the period 

 of the latitude variation was about 427 days. He showed that the 

 observations of the eighties and nineties could be represented very well 

 by assuming that the axis of figure of the earth revolves about the axis 

 of rotation in a circle of thirty feet radius in a period of 427 days. 



Dr. Chandler's investigations of earlier observations, which run 

 back as far as Bradley's classic observations for the determination of 

 the constants of precession and nutation made with a zenith tube in the 

 early part of the eighteenth century, seem to show that the period of 

 variation was formerly considerably shorter than at present, the observa- 

 tions of the eighteenth century seeming to demand a period of about 

 370 days. Later observations showed also that the amplitude of the 

 change is not constant, so that the change in latitude can not be accu- 

 rately represented by assuming that one axis revolves about the other 

 in a circle of thirty feet radius. Chandler's later conclusion is that 



