",, ". 



( 485 ) 



+ 



+ 



O a, 

 O ,1. 



-f- 



+ 



= O. 



Tl" wc repivsoiil llic minor of t/;/. in Z- = ^' 4- ^/^ ^ r/., , ^r,,, ^/^ , In 

 .I//.-, il ensues from liiis relation llial llie loens of llie ])oint /' i.^ 

 indienled l>y llie lollowinu- eqnalion (where llie indiees of ihc coor- 

 dinates are left onl) 



So the loens of the jioijils of inlers(M"tion of Irijtlcis of niiilnallv 

 perpendienlar tanuenl |>laiies of S- is a sphere (Moncjk). 



The tanjienlial eone lo S' with \erle.\ /' possessing- three inninallv 

 [x'rpendienlar tanucnl planes, the laiiuent j>lan('s form aeeordiiiii' to 

 a well-kjiown property an inlinite iinmher of lri|»lels of miilnalh 

 )>erj)endienlar planes. 



Foi' .1,, = {) we lind S'^ to ix' a paral>oloi<l and the sphere ol 

 AIon<;k degenerates into a plane. 



The ohtaincd «'(piation can i)e replaced by 



Now however JjjJ,, — J"-',, is e(pial to (",,.",•,:, — "",..,)/-. M 

 The I'adins of the sphere is indicale(l liy the sipiare root oiii of 



L 

 A\^ 3 

 Coiisefpiently the sphere of AloN(;r, will l>e rednced lo a poiiil- 

 spheiT' when >S-' is a cone {L=zz{)) or iiilo an eipiilaleral liy perhohtid 

 if jjaniely the ecpiatioji 



^) This endues iiilci- alia frem 



'Si "i2 f'i3 «u i m'ii ^^ 



«M ".J ".:. 'Si \. *^ 



X 

 1 A, 



a 



t( 





(t 



31 



J4 



Ml 



a. 





 1 



a. 





 

 

 L 



(Sec a. 0. Baltzer, Determiuauten, Ölh edition, p. 03;. 



