237 
minated by the axis of x, and a parallel line through 
P, so that PO = mBR; on this curve take a point of 
which the ordinate is equal to and draw through 
this point a line LM parallel to the axis of x and of length 
mEF so that the curve bisects the line. Then L and M 
will be points on the projectrix, it is possible that the 
curves on which the ylie may be discontinuous, Xi and Xz 
being abscissse of the points L and M, and x and y being 
co-ordinates of the point of intersection of the line LM and 
the curve HK, we have the following relations : 
x.2-Xi = LM = ?/^EF 
X2 + Xi 
y =• mRG. 
By the equation to the primitive curve we have 
EF = 0(RG) 
and by the equation to the curve HK we have 
x = xP{y), 
by substitution we obtain the equation 
By a similar method of procedure we may draw below the 
axis of Ox that portion of the projectrix corresponding to 
the portion CAD of the primitive. 
The Peesident pointed out the importance of the fossil 
Coniferse in relation to the Darwinian philosophy, and the 
consequent value of every fragment, the relations of which 
to living forms were capable of approximately exact deter- 
mination. He then described a silicified cone of Abies 
oblonga of Bindley Hutton, found on the Sidmouth coast ; 
and which had, in all probabilities, been washed out of the 
Lower Green-sand. The specimen was remarkable for the 
exquisite manner in which the details of its structure were 
