162 Practical Method for cutting Spherical Brick Niches. 
be drawn up to the line 5 m, and from thence described round 
to the radial lines 4, 3. If these lines are now brought dowi 
to intersect the par: Hel tines on the ichnography, the intersec- 
tions will then give the poiats th rough which the curves must 
pass, as seen described on the centring. These lines being now 
shown ichnographicaliy on the centring, it is next required to 
make a mould for drawing them mechanically on the centring, 
and for gauging the edge of the templet c,c,c,z: this is done 
most expeditiously (and sufficiently accurate for the workman) 
in the following manner: Take the four numerical divisions 
from the plan and set them on the line 1254 at fig. B; 
these lines then draw parallel to gg, and bring up from the 
plan of the centring the cerresponding lines ee, &c. and where 
ee intersect the parallel lines 1234 will be the extreme 
edge of the mould. The other edge of the mould is found 
by merely transierring the distances on the opposite side of 
the centre line. The rule f shows a mechanical method, as 
used by some workinen far striking the joints on the centring 5 
but as it is liable to variation, I shall merely explain it: A rule 
is first fixed at the centre 7, and in the direction of any joint 
divided round the arch; a string is then fixed at the back of 
the centring opposite 7, and the other end of the string brought 
to the upper edge of the rule, and from tiat slided “gradually 
down on the centring in the direction of the rule. The joint is 
then marked by the line with a pencil. 
I now proceed with the moulds and templets for gan- 
ging and rubbing the bricks by; dddd represents the ground 
(glued up like a piece of dade) towhich the inclined wedge-like 
mould cee is fixed. This mould requires to be very accurately 
made, as it becomes the regulating mould of all the bricks 
throughout the niche, and to which the bricks are fitted; aa 
shows the section of the hither end of the mould, which ends 
imperceptibly in a thin edge at 7, likewise inclining to p, where 
it will also fall to a point: the edge ccc also curving round 
agreeably to the mould wx shown above, and swelled by the 
mould, fig. B, being bent ronnd it. ‘The mould aa, observe, 
must be the exact thickness of one of the bricks taken from the 
elevation, as g, 0, for instance; but here the mould is shown as 
if the bricks were six times as large, This is to make it more 
evident. 
The mould*being now made and screwed on the grounds, 
next mark the divisions of the bricks round the edge of the 
mould ccc, likewise on the grounds, which divisions draw to- 
wards p by means of arule. This will now give the mould for 
the thickness, inclination and joint, of every required brick, and 
Lilli, 
