30 VARIABLES AND FUNCTIONS. [INT. II. 



Therefore 



9X 2# / # 2 z z* 



\ 



ax 



8s ~ (c 2 + X) F' (X) ' 

 The parameter of the point-function X is accordingly given by 



8x 



*_L_*_.+ f + ^ 



_,./ /-v \\o I / o . -v \o I /To i ^\o / n 



that is 



y (X)) 2 ((a 2 + X) 2 ' (6 2 +X) 2 ' (C 2 + X) 2 J ' 

 4 



Now the direction cosines of the normal to the surface 

 X = const, are 



1 8X 

 (7) c 



_ , ^ \ /v / "" _ i 



O * /~2 i ^V \ ET/'X 



Similarly for the normals to the surface //. = const., 



/ \ x 



cos (n^x) = - 



COS WuV = + - 



cos (rinZ) + 



- 



The angle between the normals to X and JJL is given by 



