GROIN. 
rule, obferving to reverfe the lines that are upon the fame 
fide toeach other. To fave time in fitting the boards of the 
tranfept, a mould is made for the fuperficies of the ungula.of 
this vault in the fame manner. The boards for the covering 
are laid together upon a flat furface, to the breadth of the 
circumference of the vault, and a line is to be drawn 
the edge of this mould acrofs the ends of the boards, 
mould at the proper angle from the 
D, N° 4, is half a rib of the nave ; the 
5 
se 
p> % equal to 
and it wi be 
ut as the arc may be di- 
vided into equal parts which form fegments, whofe chords 
differ in length, but an exceeding {mall quantity. from the 
are itfelf, ‘Thefe chords, repeated to the number of divifions 
upon a ftraight line,’ will give the reification of 
_ the curve nearly. When the rib of the nave js a femi-ellipfis, 
and of the tranfept a femi-circle, it may be found very 
i frit into e 
are upon the tranfverfe axis is much quicker towards each 
extreme than at the middle 
Groin Ribbing. 
oins are tho 
ie turned upon a centre, . 
common 
rig 
the other, in which they are all ftraight, and placed paral 
nods is fhewn at A BC » fig: 33 
and the conflruction on the right-hand 
From 
perpendiculars for the. ellipfis 
I KL equal to thofe of the femi-circle ; from the interfee- 
tions on either diagonal, draw perpendiculars to that diago- 
nal, on either fide of it; make thefe perpendiculars alio 
equal to thofe of the femi-circle. 
gives double the ftrength, but occupies lefs fpacé, and is 
t has long been experienced, and univerfally ackno 
ledged, that the prefent eftablithed method of erecting 
groined arches is a weak and imperfeét conftruétion, and, 
COMPANY improper to be introduced into warehoufes, 
acta yaa 
uch other buildings as require a much greater degree of — 
‘ftrength and folidity than is ufual, in order to fupport, with 
e weights and burthens which are _ 
nl. 
more fafety, the imme 
conttantly placed therei 
But, notwithftandin ng 
) 
ding this general opinion, I have 
heard that any profe ualified 
as bd mat 
though it is unanmmoufly 
would be attended with confiderable commercial 
| advantage. 
Indeed, upon a flight Seon of the fubje&, the — 4 
of arches, as they are now 
jeCtions raifed againit this kind 
uilt, appear to be too well founded to require much com- 
In the firft place, it muft be manifelt to every obferver | 
examines them, t . a very material part of the fubftance 
of the bricks, forming the groined angle, is pared and 
away, with an i 
intent of producing additional length to | 
as 3 ‘ Ree 
