



till the ootodinates of ei satwfyequat 



.I..N.--I. it t ruoes a plane surface ; 

 tin- ^ y-i'l.iiH- ; and, a* evidently the coordinate* 

 m -I- not natiufy equal 



i ( \ ). 

 -am: the equation 



r* 



i the yj-plane a circle. It is therefore satisfied 

 l-\ the coordinates of any point Q, in a line parallel to the 



jr-axi>. thin; point P of this circle; and also by 



the coordinates of Q as thin line PQ is moved, parallel to 



f , 



r-axis and along t)i< rcular cylinder thus 



traced i.\ the line PQ* perpendicular to the yj-phiut . 

 the locus of t 11 equation. 



.lilarly, it may be shown that the locus of the equat 



Sri*- 1 () 



IB a cylindrical surface tia.-ed by a Straight line parallel to 

 the y-axis, and moving along the hyperbola whose eqtur 

 in the j-j-plaiie is equation (8). And, in general, it is clear 

 !ialog\ that hroic equation IN tiro variable t reprt- 



a < irfac* wkote eltmtnt* art parallel to th* 



