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pare a project for the defence of an important channel ; and 
having been convinced, while employed as an assistant in the 
construction of two of the batteries just mentioned, that the 
principles and the details by which the embrasures and the 
dependent casemates had thus far been regulated were erro- 
neous and defective, set about a careful study of the condi- 
tions to be fulfilled in providing for the heavy guns of that 
period, mounted on a casemate carriage that had already 
been approved and adopted. The result was an embrasure, 
having an exterior opening of 4 feet wide by 2! 6” high at 
the outside line of the cheeks, and three feet high at the key 
of the covering arch, the throat being 1’ 10” wide. This 
provided for all the depression and elevation of the gun that 
the carriage permitted, and also for a horizontal scope of 
full 60 degrees. Covered with a lintel instead of an arch, 
the height of the exterior opening might be a little less 
than three feet. ; 
“The plan of this embrasure shows that the interior 
opening is 5’ 6” wide, and that the plane of the throat 1 
within 2 feet of the outside of the wall, which just at the 
embrasure is five feet thick. 
“A slight modification fitted this embrasure, when applied 
to flanking or interior defence, to receive at first a carronade 
of large calibre, and of later years, a howitzer instead. When 
these latter were liable to be assailed by musketry, the outer 
cheeks were made en eremailliere (notched), — a long-know" 
device. 
“Tt was with timidity and hesitation that the cheeks and 
this embrasure were placed so near the track of the ball, 
when fired from the casemate, with the maximum obliquity, 
and the results of an early trial with experimental embra- 
sures at Fort Monroe gave some sanction to the doubt 
The first two undér trial were built of lime mortar, and 
