THE ROYAL ARTILLERY INSTITUTION. 
53 
and four 2|-in. The cellular backing was the same as in No. 1 plate, but 
the cells were filled with teak instead of millboard. 
No. 3 Plate measured 7 ft. 6 in. by 2 ft., and was 4 in. thick; but on its 
back were formed three vertical projecting ribs 2J-in. deep and about 9 in. 
wide, in which ribs vertical dovetail slots were cut to receive the dovetail 
bars, which were very similar to those in No. 1 plate; these dovetail bars 
had six 2^-in. bolts attached to them. 
The cellular backing was similar to that in the two former cases, only that 
the angle irons were made of f-in. iron instead of inch, and the filling was of 
millboard. 
No. 4 Plate was the same as No. 3, only that the filling in the cells was 
of teak instead of millboard. 
No. 5 Plate measured 6 ft. by 4 ft., and was 4 in. thick, with ribs at the 
back, and slots as in Nos. 3 and 4 plates. It was held on by twelve 2J-in. 
bolts, attached to three continuous heads. The cellular backing was the 
same as that of Nos. 3 and 4 plates, and the filling of teak. 
No. 6 Plate measured 6 ft. by 3 ft., and was 3 in. thick, and had at the 
back 4 horizontal ribs, across which, in a vertical direction, were cut three 
slots to receive three continuous heads as before, to each of which were 
attached three holding-on bolts; six of these nine bolts were 3 inches in 
diameter, and three were 2J in. The cellular backing was formed of vertical 
angle irons 6| in. by 3J in. by \ in., and thus the cells ran vertically and 
were 6J in. deep and 4 J in. wide; the filling was of millboard. The structure, 
in this case, received additional support through some stiffening pieces or 
double knees attached to the ribs of the ship and abutting against the back 
of the skin. 
No. 7 Plate measured 7 ft. 6 in. by 3 ft., and was 3 in. thick, with three 
vertical projecting ribs at the back, very similar to those on plates 3, 4, and 
6. There were three continuous heads running vertically in the three ribs, 
and to each head were attached two 2 J-in. and one 3-in. bolt. 
The cellular backing was composed of double angle irons 9 in. by 2\ in. 
by \ in., forming horizontal cells 8J in. deep and 4 in. wide, filled with teak. 
Teak was also filled in at the back of the skin between the ribs, and the ribs 
were likewise-stiffened in a similar manner to those in No. 6. 
The iron representing the skin of the ship was \ in. thick, and the ribs 
10 in. deep, and 15 in. apart. 
The weight, per foot superficial, varied in the different plates : that of 
No. 6 was the greatest, and No. 5 the least. 
The average of the whole was about 375 lbs. per foot superficial, of which 
about 25 lbs. were due to extra support given at the sides, top, and bottom of 
the target. 
The guns used in the experiment were the 68-pr. service, the 110-pr. 
Armstrong, the smooth-bore muzzle-loading Armstrong 9-in. (6 ton) gun, 
and the lO^-in. Armstrong (12 ton) gun—all at 200 yds. 
The firing commenced with two live shells from the 68-pr., and one from 
