THE ROYAL ARTILLERY INSTITUTION. 
45 
At the end, representing the 10-ft. shield, the strut, being brought nearer 
to the embrasure than the other one, was splayed outwards at an angle of 
15° from the perpendicular, as this would be necessary in actual practice to 
admit of the gun being traversed through an arc of 7 0°. The other strut 
stood perpendicular to the shield. 
Between the surfaces of the front and rear planks, sheet lead, weighing 
6 lbs. per foot superficial, was introduced to check vibration in the mass ; 
and under the nuts of the screw bolts elastic washers of various descriptions 
were used. Some of these washers were of the nature of buffers, composed 
of 3 in. of india-rubber inside a strong wrought-iron cylinder; others were 
of coils of wire-rope similarly confined; and in other cases several lead 
washers, and washers of iron and brass were used. 
The shield was made by the Millwall Iron Company. 
Tor this experimental work it was of course out of the question to go to 
the expense of providing rolls for producing all the various sections of 
planks used in it, and therefore hammered iron had to be adopted for the 
face planks, yet the shield is designed with the special view of using rolled 
iron throughout in actual practice; and as upon this depends very much 
the expense of the structure, it is important that it should be mentioned 
here. 
The following guns were used on the first day's trial:— 
One 120-pr. Whitworth rifled gun. 
One 110-pr. Armstrong „ „ 
One 68-pr. Service smooth-bore gun. 
Range 200 yards. 
Twelve shot from these guns struck the shield fair, namely - 
From the 120-pr. 
From the 110-pr. 
One round-ended cast-iron shot, 119”5 lbs. 
One flat-ended homogeneous metal shot, 130 lbs. 
Three cast-iron solid shot, 110 lbs. each. 
Two „ „ 68 lbs. „ 
From the 68-pr.—Five cast-iron solid shot, 67 lbs. each. 
In all, 1050 lbs. weight of shot struck the shield on this first day's trial. 
The effects produced were highly satisfactory. 
The indents made by the 681b. and 1101b. solid shot from the 68-pr. 
smooth-bore and Armstrong guns varied from 1T5 in. to 1*6 in.; those 
made by the 68 lb. shot from the 110-pr. were 2*3 in. and 2 in. respectively; 
and the indents of the Whitworth shot were 1*8 inch in the case of the cast- 
iron, and 2 inch in the case of the homogeneous metal, which latter shot 
broke up. 
With the exception of one small crack in a 7 in. plank, where a shot had 
struck near its edge, the shield was really none the worse for the day's 
firing. 
The lead between the planks was squeezed out a good deal under some of 
the blows, some of the lead washers were flattened, and other minor effects 
were visible, but nothing to render the shield at all unserviceable. 
Such being the case, it was determined to reserve it for the Armstrong 
300 lb. rifle projectiles, and a batch of other monster guns soon expected to 
be ready. 
