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comparatively ignorant), but as in the case of field works to render tbe effects 
of shells less destructive, and to have more earth at hand for the repairs of 
damages. This thickness has been made from 20 to 27 ft. in some of the new 
works at the dockyards. Some recent Trench works give 21 ft. Secondly, 
the lowering of the top of the scarp, so that instead of being in a plane 
passing through the crest of the glacis and the most commanding point the 
enemy can occupy within range, it may be some feet below that plane, to 
avoid the risk of any considerable height of it being breached by a distant 
curved fire. This will be particularly necessary where an independent wall 
or one with a chemin des rondes may be employed. As this lowering of the 
escarp will, if the bottom of the ditch is horizontal, render necessary a very 
high counterscarp, the bottom of the ditch may be sloped upwards towards 
the counterscarp, so as to reduce the height of the latter. With the same 
object of diminishing the risk from distant curved fire, the ditch should be 
made as narrow as practicable, so as to bring the crest of the glacis as near 
the wall as may be. 
While the lowering of the scarp and narrowing of the ditch are necessitated 
by the improvements in distant curved fire, breaching the escarp from batteries 
on the crest of the glacis will be also thus rendered more difficult. 
Captain Tyler, E.E., in a lecture delivered by him at the United Service 
Institution, in March, 1860, advocates the abandonment of the escarp 
altogether, substituting for it a counterscarp, about twice the usual height. 
By this arrangement a besieger after blowing in the counterscarp, which, 
whether it were a high or low one, would be an operation of much the same 
difficulty, would have no further obstacle to overcome, and would be spared 
the danger and delay of constructing breaching batteries on the crest of 
glacis. 
With regard to trace, as far as flanking the ditch is concerned, it does 
not seem desirable to increase the length of lines of defence beyond the 
range of case, or at any rate of grape shot, unless it is found that the 
segment shell or some similar projectile can be made to produce equally 
certain effects at short as well as at long ranges. 
It will be absolutely essential that the flanking works, if casemated, should 
either be so placed that their walls and embrasures should not be liable to 
injury from distant fire from batteries in the prolongations of the ditches, (by 
which from the experience gained in Germany in 1857, and at Juliers in 1860, 
they could certainly be destroyed), or, should it not be practicable to trace 
the ditches so that their prolongations may fall on ground that the enemy 
cannot take up, the fronts of the casemates must be then either iron plated, 
or a plan may be adopted, recommended by M. Piron, an officer of the 
Belgian Engineers, in a work called “ La Fortification Eclectique,” and carried 
out, I believe, in the new works at Diest in Belgium. It consists in placing 
a mask or counterguard parallel to, and about 10 yds. from, the wall of the 
casemate, with arches running through it, the piers of which coincide with 
those of the casemate. The height of the arches is regulated so as to 
conceal the embrasures from a battery on the crest of the glacis. To prevent 
the debris of the piers and arches, when being breached, from masking the 
embrasures, a small ditch may be excavated under the front of each arch. 
M. Piron calculates that with a counterguard 20 yds. thick, it would take 
88 hours continuous firing from two 24-prs. at a range of 400 yds., to destroy 
