359] 
A SUPPLEMENTARY MEMOIR ON CAUSTICS. 
463 
For m — < f>V2, the loop has altered its form in such wise as to exhibit the 
node and two cusps, the curve has therefore two real nodes. 
For m = V2, the two nodes 
the point of disappearing; and 
thus no longer any loop. 
unite together into a tacnode, so that the loop is on 
for m<V2>1 the nodes are imaginary, and there is