178 Journal of the Asiatic Society of Bengal. [ April, 1908.] 
dat dy2 
Bdaa2z Sdydty 
3(d2x)? + 4dad2x 3( dy)? + 4dyd2y 
10d2zd3z2 + 5dzed4x 10d2yd3y + 5dydty 
2dady dadty — dyd» 
3(dzd2y+dy dx) dediy —dydix =0 (49). 
6d2ad2y +4(daedys + dyd3zx), dadty —dyd4+e 
10(d2xd3y + d8zd2y) + 5(dadty+dydtx), dxdby—dydby 
which is therefore the condition that the conic of closest contact 
at any point of a curve may be statio 
f the independent variable be z, then equation (49) reduces 
to 
40r° — 45grs + 9q3t=0 (50). 
which is the differential equation of the general conic, as has been 
deduced by Monge. 
For further information on the Mongean equation, reference 
may be made to Asutosh Mukhopadhyaya’s paper, ‘mentioned 
in the introductio: 
a a Oe 
