94 



goes along the hyperbolic circles, tlie elliptic circles interchanging. If 

 mod. = 1, amp. =f o, motion goes along elliptic circles, the hyperbolic 

 system being invariant. If mod. ±1, amp, =fO, motion is along neither family 

 but passes diagonally from curvilinear rectangle to curvilinear rectangle. 

 These respective transformations may be named hyperbolic, elliptic, loxodromir. 

 The circles about and through the fundameutal poiuts are potential lines 

 and lines of flow iu tlie well known problem of electricity of equ.il source 

 and sink. 



Bloomington, IxD., Nov. 28, 1906 



