CONTINUOUS CALCULATING MACHINES. 
381 
The motion of B when the pointer passes along gV'li is 
—jy 1 <i£c=area of curve gVhrnl 
because the roller A is moving in the opposite direction, and dx is negative. 
Finally, the result shown by the index is 
| y,dx — | y x dx = f (y z - y x )dx 
=1 
PP 'dx—\% 
= area VgVh 
The same result might have been obtained with the sine arrangement (fig. 16), but 
now either the top or bottom roller in the movable frame must travel along the line of 
ordinates, and the point N be the centre of rotation for the end of the drum on 
MDCCCLXXXV. 3 D 
