1809.] 
equally thick throughout.* A perusal of 
Dr. Gregory’s paper will shew, not only 
that he has not said egwal, but also, that 
he never meancit; yet scarcely was the 
ink dry, whereby this second misrepre= 
xX 
‘Let it be admitted, that the mode, by 
which the author of a Treatise of Arches 
and Abutment-Piers describes the cate- 
naria, is correct, and that X A Y is the 
line so described, cz being the diame- 
eee a a ena 
* See page 37, Dr, Hutton’s Principles of 
Bridges. 
Theory of the E quilibration of Arches. 
171i 
sentation had been made, when either an 
injudicious friend, or concealed enemy,, 
of the Emerson theory of arches, boldly 
defends what Dr. Gregory or Dr, Hutton — 
never thought or dreamt of, 
— 
a 
ter of the generating circle and eA 
the constant right line. : 
By Prop. 7. Corol. 8. of Dr. Grego- 
ry’s paper—If AR be taken equal to 
the chain A D; and the right line BR 
Le drawn and bisected, and from the 
point of bisection a right line at right 
anzies to BR be drawn, intersecting 
BA protracted in C ; C will be the 
: sentre 
