are called the lines of defence, giving B t 
and C w for the faces of the two bastions. 
With the opening tw, measure tv, and w u, 
on the lines of defence, to determine their 
proper lengths,- so as to give uv for the 
length and position of the curtain ; next 
draw the lines t v, and w v, either curved or 
straight, for the flanks of the bastions. If 
they ai e to be curved, which are generally 
preferred, the points t and jo, will be the 
centres of equal circles, whereof the two 
flanks will be equal segments. 
Proceed in the same manner with the 
other two fronts, A B and C D ; you will 
thus complete two bastions, 3 and 4, and 
the halves of two more, 2 and 5. Is ext 
measure off 15 toises, and draw something 
less than quadrants, or quarters of circles, 
from the points B and C j the centres ot 
those quadrants being exactly opposite 
thereto, place your scale so that you may 
draw lines from the ends of the quadrants 
towards the shoulders of the bastions, but 
draw no further than suffices to touch upon 
the perpendicular of 30 toises : thus your 
scale would give the direction, l tv, but your 
line would stop a little below d. This being 
done in both directions, and throughout the 
three faces, will give the width of the ditch, 
and the interior lines or re-entering angles 
of the ravelines O, N, K. The body of 
the raveline is formed by measuring 10 
toises on the face of each bastion, setting 
off from the shoulders t tv tow ards the sa- 
liant, or projecting angles, (here called 
flanked angles,) B and C. An opening of 
the compasses equal to u w, (or to t v,) with 
the ten toises included, will give the dis- 
tance of the saliant angle o, of the raveline 
N, from the centre S, of the curtain uv. 
The sides, or faces of the raveline are deter- 
mined by lines, drawn from the saliant an- 
gle to those points on the faces of the bas- 
tions 3 and 4, already set off at 10 toises 
each, from their respective shoulders t and w. 
It should have been stated, that all angles 
projecting outwArd from the body of the 
place, are called saliant angles: for in- 
stance, s, B, t, of bastion 3, and e, o, e, of the 
raveline N : while such angles as point in- 
wards towards the body of the place, are 
designated re-entering angles ; such t, u, w, 
on the lines of defence of the centre face. 
When an angle re-enters at such a position 
in the outworks, that its apex, or point, 
cannot be seen, and consequently cannot 
be defended front the body of the place, 
it is called a dead angle. Such cannot 
easily take place where the smallest atten- 
tion is paid to the most ordinary rules ; but 
wherever found, should be exploded from 
the defences, either by cutting off a large 
part of the pinch, or narrowest part, and 
substituting a curtain, or by new modelling 
the defences in that part. It may be proper 
to observe in this place, that works in- 
tended for mutual defence, should never 
exceed an angle of 120 degrees, nor be less 
than 60. The medium, i.e. 90, which 
forms a right angle, generally considered, is 
indisputably the best for the above pur- 
pose. Where batteries stand at such an 
opening, that their direct fire, that is im- 
mediately to their own front, is parallel 
with the front of the part they flank, it is 
called a razant, or grazing tire ; but when 
the angle is less than 90, so that the direct 
fire would strike upon the face of the work 
to be defended, it is termed fishant, or 
plonging : both have their uses, but the 
latter is rarely adopted, except from neces- 
sity, because a direct fire, at right angles, 
may be made to plonge, by giving the can- 
non an inclination more parallel with the 
side of the embrasure, which being angular, 
allows a deviation of many degrees from 
the direct fire. 
When two lines form a very acute angle 
with each other, they no longer are de- 
fences ; for in case the enemy should carry 
either of them, he would be able to work 
its battery against the other line ; and 
though the fire would be plonging, and 
that too at a great disadvantage, yet as 
many shots would light within the embra- 
sures, the parapet would speedily be des- 
troyed. Therevetement, or masonry, in the 
front of the line so plonged, would not be 
much hurt, as it would turn off the shots. 
Before we proceed farther, it is expe- 
dient that the reader should examine the 
line of the principal, following along A, o, 
S, r, s, B, t, u, v, w , C, b, y, z, m, D ; in all 
which he will perceive, that every part is 
made to flank some other. The ravelines 
O, N, K, will be found to give great secu- 
rity to their several curtains, sr, u v, and 
yz; while at the same time they would 
enfilade whatever approaches might be 
made towards the saliant angles of the bas- 
tions. In examining these circumstances, 
all the other outworks must be exempted 
from consideration ; our view must be con- 
fined to the manner in which the gates in 
the curtains are protected ; the flanks of 
the bastions concealed from every part, 
but the line of their direct fire ; and the 
spaces opposite the saliant angles, subjected 
