180%}. 
on its blade; or of a pyramid inverted 
without even the appearance of any di- 
rect lateral support: as is more fully and 
practically demonstrated hy the separate 
fragment (made tora large scale) apper- 
taining to the model of the commen groll- 
ed arches. 
Thus having, I presume, sufficjently 
proved that the old or usual method of 
building the common groined arches 1s 
diametrically opposite “to every sound 
principle of mechanical art or science ; 
and no less contrary to the simple axioms 
of common sense, because they are found 
to be most inadequate i in point of strength 
where force is most required, and most 
introduced where they ought never to be 
admitted; which perhaps results from 
this plain reason, that no others have ever 
yet been recommended as better calcu- 
lated to supply their place: 
I will, therefore, now proceed to givea 
concise description of my new method of 
building them, referring my readers, at 
the same time, to the consideration of the 
medel made for that purpose; which 
though consisting of a single arch only, 
will never theless impart a competent idea 
of a continuation of them, where circum- 
stances may render a multiplicity neces- 
sary. 
Instead of the square piers, so com- 
monly used, I have adopted octangular* 
ones, being essentially requisite to. the 
principles of the new method. . Also, 
they occupy, of course, less space on 
the ground than the sguare piers of 
the same dimensions taken transversely ; 
nor are they so liable to be injured 
at the anglest, by the rolling of casks 
or removal cf goods, as those which are 
square. The octagonal piers, measured 
across each way trom the foot of the 
ribs, are four feet eight inches, which is 
the size of the square ones used in the to- 
bacco warehouses of the London Docks. 
But the octagenal piers are attended with 
this superior ahd apparent advantage: in 
each of them there will be a saving of 
room, amounting to five feet eight inches; 
* They are called octangular, because they 
resemble the true octagon more than any 
other figure. 
+ By filling up the four-inch recesses be- 
tween the bases of the ribs to the height of 
the springing course, the piers would be- 
come perfectly octangular; and consequent. 
Jy all the angles, by being obtuse, would be 
less liable to harm than they are even by this 
method: but some small space on the plan 
weuld be lost. 
On anunproved Method of building 
« 
groimed Arches. 142% 
which arises from the truncation of the 
four triangles produced by the generation 
of an octagon within a square. Phat is 
to say, each of the square piers in the to-~ 
bacco warehouses of the London Docks, 
though only the same size from out to out, 
occupy five feet eight inches mere of the. 
area or superficial contents of the ware- 
house than the octagonal piers: which 
sum multiplied by the number of their, 
throughout the whole building, would 
amount to a considerable loss of room in. 
regard to stowage. And here it ought 
particularly to he observed, that, though 
the octangular piers contain less sub- 
stance, by cutting off the four angles, 
than the others, they are neverthe- 
Jess much stronger owing to the straight 
direction in which the cross-ribs of the 
contiguous arches reciprocally support 
and resist each other, independently of 
the intervening spandrils which are to be 
brought up as usual to the level of the un- 
der-side of the crown of the arches: 
whereas the angles in the common groin= 
ed arches, and which, as before observ-~ 
ec, are the parts where the greatest effort 
of resistance ought to be made, have no- 
thing else to rest upon than the most 
flimsey of all bases, namely an extreme 
corner of a square pier. 
The distance of these octangular piers 
from-each other, i have supposed to be 
twenty-one feet; which.also tallies with 
the space observed in the tobacco-ware- 
houses at the London Docks, and which 
has been vroved by experience to be an 
advantageous distance between the piers, 
for the accommodation of various stew- 
age, in large warehouses. At the same 
time, I only allude to these works as of 
national notoriety, end very justly of pub- 
lic approval, by way of datum; ‘since it 
is clear to every understanding, that. the 
new method, as well as the old, may be 
practised with equal ease to Buy dimen= 
sions, and with any kind of arch.* 
I have intended the diagonal ribs to 
consist of two bricks and a half on the 
face, and two bricks in thickness; which 
may also be made larger or smailer, agree= 
ably to the span of the arch, the size of 
the piers, or the ratio of weight designed 
* Should any one prefer the cross-ribs to 
be semicircular, or any other sort of arch, in-= 
stead of the elliptic ones observed in the mo- 
. del, then the filling-in arches will followthe 
nature of the curve, whatever it may be: 
but this difference in the choice of the arch 
produces no alteration whatever in tie real 
principles of the new saat hede 
~ 
