Nov. 2, 1882 | 
NATURE Ae 
homogeneous gun, such for instance as a solid cast-steel 
gun as formerly made by Krupp, and we will assume it 
to beg inches calibre, and 15 inches thick at the breech 
end, and that it is subjected to an internal pressure of 24 
tons per square inch. Now it is evident that the total 
strain to be resisted is 9 times 24 tons, or 216 tons, one 
half of which, or 108 tons must be borne by each side of 
the gun, or by a thickness of 15 inches of steel. If there- 
fore the strain could be uniformly distributed, it would 
not exceed = or 7'2 tons per square inch, but in reality 
I 
the strain at the inside circumference would be nearly 27 
tons per square inch, whilst at the exterior of the gun it 
would be only 24 tons per square inch. 
The subjoined diagram (A) represents the condition of 
30 
10 | C, 
25 
20 
16 
strain of such a gun under these circumstances. The 
abscissze denote the distances from the centre of the bore, 
whilst the corresponding ordinates denote the strains in 
tons per square inch at these distances. 
In the next place let us examine the condition of strain 
of a gun of the same calibre, but composed of an internal 
steel tube 33 inches thick upon which is shrunk a wrought- 
iron hoop 122 inches thick with a shrinking of 1 in a thou- 
sand, This was the Woolwich construction for all guns 
up to 9-inch calibre up to 1869. 
Subjected to an internal pressure of 24 tons per 
square inch, the diagram B, shows the induced strains. 
Previous to the internal pressure being applied, diagram 
B, shows that the steel tube would be compressed by 
the outer wrought-iron hoop. The compression would 
be 11°7 tons per square inch at the inner and 7°86 tons at 
the outer circumference ; on the other hand the wrought- 
iron hoop would be in a state of tension, 5°19 tons per 
square inch at the inner and 1°38 tons at the outer cir- 
cumference. When the internal pressure of 24 tons per 
square inch is applied, the diagram B, shows the con- 
dition of strain. The steel tube would be strained to 
15°53 tons per square inch at the inner, but only to 2°67 
tons at the outer circumference, whilst for the wrought 
iron hoop the strains would be 15'09 and 4 tons respec- 
tively per square inch. Thus it appears that comparing 
this gun with the homogeneous gun of the same size and 
under the same conditions the maximum strain has been 
reduced from 27 tons to 15°83 tons per square inch. 
Pursuing the matter further let us examine the con- 
ditions of Sir Joseph Whitworth’s 12-inch gun, built up of 
a steel tube 4°35 inches thick, on which are placed four 
successive steel hoops, each of 5°55 inches thick, the 
TONS PER SQ. INCH, TENSION. 
10" TONS PER SQ.INCH, COMPRESSION 
(S ;-TONS PER SQ.INCH. TENSION. 
ee IN eis. 
15 —TONS PER SQ.INCH. TENSION 
total thickness of the gun being thus 223 inches. Before 
proceeding to the examination of the strains in this gun, 
it is desirable to devote a moment or two to the very 
important question of the amount of initial strains with 
which hoops should be put on. The Woolwich practice 
is to adopt a uniform shrinkage of 1 in a 1000, that is to 
say, the internal diameter of each hoop is 999/1000ths of 
the external diameter of the hoop below it. The outer 
hoop is expanded by heat, placed over the inner one, and 
then in cooling grips it with the force due toa contraction 
of 1/1oooth of its size. This is a fundamental error in 
the Woolwich practice, and it is mainly from their per- 
sistence in this error that so many Woolwich guns have 
failed. The proper amount of shrinkage is not a fixed 
amount. It depends on the thickness of the rings, their 
position in the structure, and the modulus of elasticity of 
the material, and it is only by a due regard to these 
