578 PROFESSOR CAYLEY ON THE SEXTACTIC POINTS OF A PLANE CURVE. 
73. For the third line, substituting for V 2 dU its value =d>BH— Hdd>, we have 
2$ 2 
third line of d 2 d 3 U= — H<3<f>). 
74. Hence, uniting the three lines, we have 
3?3»U = ^Ay s ((m -2)H3<K+ 4>3H) 
+ (^( -2H34.+ 
+ (^^53((2m- 2 ) H 34>+(-2m+2)4>aH), 
and reducing, we have the above-mentioned value of d 2 c) 3 U. 
