Recent Progress in Theoretical Physics. 



249 



a quarter of a complete oscillation. If there be two equal and op- 

 posite tendencies operating upon F, one to carry it toward Y, 

 and the other toward X, the result will be, that the tanarential 

 tendencies at P will neutralize each other, while the normal com- 

 ponents will coincide and carry the particle towards C along r (Fig. 

 11), and a rectilinear motion 

 will be the result, as in Fig. 

 12 or Fig. 13. Thus two tend- 

 encies to gyrate in opposite 

 directions may result in mere 

 rectilinear vibrations. If one 

 Fig. 12. of these 



tenden- 

 cies be 

 stronger 

 than the 

 other, so 

 that of it- 

 self It would produce a more rapid rotation in its direction, than 

 the other component in its, then the motion will be elliptical in an 

 orbit of which the major axis changes at each complete oscillation 



by some angle d, the magnitude 

 of which will depend upon the 

 excess of velocity in one direc- 

 tion over that in the opposite. 

 This is easily seen by reference 

 to Figs. 14 or 

 lo, where the 

 motion would 

 be alonsf ab, 

 were both cir- 

 cular compo- \ 

 nents equal, 

 whereas the 



'The engraver has very imperfectly copied the origiaal drawings for this 

 as for some of the other figures. 



'For c in the figure, read ff, and for a and b at the extremities of one of the 

 diameters, read a' and b', respectively. 



