434 THE POPULAR SCIENCE MONTHLY 



the one axis about the other could be accurately computed if the exact 

 form of the earth, the structure of the earth's interior and its coefficient 

 of elasticity were known. 



In addition there are other phenomena, namely, volcanoes and 

 earthquakes, through which considerable quantities of matter may be 

 displaced. That the amplitude of the polar motion might be affected 

 by earthquakes was pointed out by Professor Milne ten or fifteen years 

 ago and a French scientist has more recently compiled a table showing 

 the number of severe earthquakes each year and the amplitude of the 

 polar displacement. A rough proportionality between the two seems 

 to exist, that is, the greater the number of earthquakes each year the 

 greater the amplitude of the polar displacement. Such results, how- 

 ever, are to be taken with several grains of allowance. The term 

 " severe earthquakes " is rather indefinite and by modifying its defini- 

 tion quite a variety of results may be obtained from the given data. 

 It might be pointed out that in 1906, the year of the great earthquakes 

 in California and Chile, the amplitude of the polar displacement was 

 small. 



We have then a rational explanation of the phenomenon of the 

 variation of latitude. The axis upon which the earth rotates is not 

 in exact coincidence with the shortest axis ; such being the case, accord- 

 ing to the principles of dynamics, the axis of figure must revolve around 

 the axis of rotation giving rise to the changes of latitude. But on 

 account of the changes incessantly taking place in the distribution of 

 matter upon the earth's surface, and perhaps also within the surface, 

 the amplitude of the polar displacement, and perhaps the principal 

 period of revolution of the one axis about the other, are changeable, the 

 changes taking place in a rather complicated way according to laws as 

 yet not fully determined. 



In connection with this explanation we should not lose sight of the 

 fact that all the material moved through meteorological, volcanic and 

 seismic agencies is probably almost infinitesimal as compared with the 

 total mass of the earth, and no one, so far as I know, has as yet shown 

 that the shifting masses are sufficient in magnitude to properly account 

 for the observed annual and other unexplained components of the 

 polar motion. 



Indeed, if one desires to follow the path of least resistance, he might 

 abandon the above explanation altogether and adopt the one given by a 

 colored preacher living in the oil region of Texas, who met some 

 brethren at the corner grocery one day and delivered himself of the 

 following explanation of this puzzling scientific phenomenon: 



Ah see by de papers dat de urf s axis am a wobbling an' dey dunno wat fo'. 

 But ah know wat makes de urf s axis wobble. Do you see all dis oil dese men 

 am a takin' out of de urf? Well wat do you spose de good Lord put dat oil in 

 dere fo'? Wy to grease de axis wif, of eouse, an' when dey take it all out, wat 

 else can de axis do but to wobble an' to squeak? 



