ORGANISATION AND EMPLOYMENT OP SIEGE ARTILLERY. 
441 
Sometimes the point at which it is required to strike the revetment 
may he reached with a less angle of descent, by firing more obliquely 
to the wall, so that there may be a greater distance between the crest 
of the glacis and the escarp, but it must be borne in mind that this 
obliquity of fire will reduce the normal energy of impact. 
It was partly to obtain a less angle of descent by allowing the pro¬ 
jectile to traverse a greater width of ditch, that in the siege of Strasbourg 
Lunette 53 was fired at so obliquely. 
The limit of oblique fire depends somewhat on the material of the Limit of 
wall; for common masonry, it is considered to be between 55° and 60°; &e for 
as stated, Lunette 53, at Strasbourg, was breached at a horizontal angle breacWn g- 
of 55°, the material being red sandstone; “at first many shots were seen 
to glance, and on account of the difficulty of making first impressions 
on the wall by single shots, two salvoes were fired from four pieces with 
the same aim, then a third salvo was fired at a spot distant 3 ft. laterally.” 
When the surface of the wall is once broken, glancing becomes less 
likely. 
A ravelin of the fortress of Gfraudenz was breached by demolition, 
the horizontal angle of impact with the face of the wall being 57° —42' 
whilst the angle of descent was 7°, and striking velocity 673 f.s.; in this 
case—thought to be the extreme limit for long shells—none of the pro¬ 
jectiles glanced. 
The French consider that the angle of obliquity should not be less 
than 60°. , 
The velocity normal to the wall varies as the sine of the angle of 
obliquity. 
The noise of impact on masonry is sharp : when the wall is cut Practical 
through the sound is dull, and the same is the case when a shell strikes ofprogress 
earth. The deeper the penetration in masonry, the longer the smoke 
takes to rise. penetration 
Till the wall is cut through the smoke is bluish-white, white or red ofshe11, 
with brickdust. When shells burst in earth behind a revetment, which 
has been cut through, the smoke is dark-grey and rises as out of a 
chimney. At Gfraudenz, splinters were observed to come back at least 
400 yds. from the masonry. 
In general, decided results will be more expeditiously obtained by a Notes on 
concentration of fire on the ordnance, breach, materiel , or troops to be e 
attacked, then, the object once attained—occasional rounds being fired 
to prevent re-armament or repairing—the mass of guns can concentrate 
on some other point. 
As a'rule, in enfilading by means of curved fire the flatter the trajec¬ 
tory and the higher the striking velocity* the greater will be the effect ; 
as the angle of descent increases, and “ high-angle fire 33 is approached, 
the striking velocity usually becomes less, whilst the shells striking 
down into the earth will not do so much damage to troops or materiel 
on the terrepleins. 
* I n certain eases a low velocity may be an advantage— e.g., if it be desired that the pieces should 
fly bade from the burst; when shells with a very high velocity burst, most of the pieces go forward. 
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