JMethod of tracing Oval Arches. | 305 
twelve oval arches; four of which are, of forty feet span, one of 
twenty five, one of twenty, &c. In fact the great facilities afforded 
for tracing the curves, and cutting the joints of the voussoirs normal 
to them, must cause their adoption wherever they are known. 
Five Centres. (Fig. 3.) Seven Centres. (Fig. 4.) 
-ab=1. AB= 6. 
bA=2. AD=18. 
AB=4.50 oo 1, 
AC=9.00 . bc=. 2. 
ca=2.704 2 CA cake 
cb =2.305 ‘De=18.252 
bd=0.399 ec= 8.111 
Ce=9.619 eb= 8.667 
Ae=0.619 db= 1.857 
Cb=9.220 da= 2.425 
dea=21° 9’ 40” bf= 0.567 
eCd=12° 31/ 44” eg= 1.124 
AaB=56° 18’ 36” Ab—1.a10 
ADc=9° 27/ 45” 
ACb=22° 37/19” 
ABa=45° 
ceb=13° 9/ B7” 
bda—22°, 22,484 
Nine Centres. (Fig. 5.) 
Aa=10 C—O Od cs 
AB= 7.5 bh= 0.683 
AE=30 : ct= 1.507 
ab= 1 dk= 2.155 
bc= 2 Am= 2.423 
cd= 3 AEd= 7° 35/ 41” 
dA= 4 dgc= 9 41 12 
Ed=30.268 cfb=13 40 57 
gd=17.025 bea=22 9 58 
g£ce=17.673 AaB=36 52 12 
fe= 7.250 AbC=59 2 10 
fb= 8.074 AcD=72 43 7 
eb= 1.590 AdE=82 24 19 
