290 



It shows that the i-a3S that bear two coinciding null-points, 

 envelop a curve of the 6''' class. 



From this it ensues that the curve (/'*)' has no other singularities 

 outside the node P. 



Combination of (1) with the equation 



produces for the curve (/y)^ by elimination of ./i- the equation 



2 [(^, ^2 - ,^T, ét) (.T, ^3 -- -T3 é^) + (.T, ^^, — .Tj ^2)-] ^\ t,. 



This is always satisfied by ï^ = (^, 5/ = 0- This was to be expected 

 as the straight lines 0,0„ 0,0t, 0^0^ must be singular rays. 



