319 
To show how rapidly the resistance of the metal in tubes diminishes 
from the centre, even using Professor Barlow’s formula, which makes 
the resistance inversely as the square of distance from the centre, I have 
made out a Table (B) of what force each successive annular inch can 
exert in a cannon 4 inches in bore and 10 inches thick. The strength 
of each ring being 1000, the numbers in the Table show the portion of 
their strength which they can use. The total strength of such a tube, it 
will be remembered, is only one-sixth what it would be if the strain 
were equally distributed. 
Taste B.—Force exerted by successive layers of Metal in a Cylinder 4 
inches inner diameter and 10 inches thick, the strain on the inner film 
being 1000. 
Force which 
could be exert- 
ed, were the 
inner 4 inches 
removed. 
Inside annularinch, . . . 666 
Second ,, FP ge a 333 
Third ,, as ie 200 
Fourth ,, fF sea etiyea 133 want b 
Fifth _,, ‘ sf iets Elie OG 857 
Sixth ,, 6 ou tes 70 643 
Seventh ,, i Serna 55 500 
Eighth ,, i) bee ee 44 400 
Ninth, iy “5 ce ee 36 327 
Tenth ,, a Rr 30 253 
Total, 1663 3000 
Theory gives the third inch a power of exerting one-fifth of its 
strength. A reference to Table A shows that Major Wade’s actual 
measurements gave only half even of this. 
_ Paradoxical though it may seem, a thick tube like this would be much 
strengthened by diminishing its thickness. 
Professor Barlow’s formula would give 6 inches as the thickness of 
maximum strength for a tube of the outer diameter of the one we have 
been considering. Its strength then would be 3000, or nearly double 
that of the thicker tube, because, the four inner rings being removed, the 
others could use more of their strength. Yet the Government is to this 
day making cannon with bores of 6 inches, and walls of nearly 12. I 
have said enough (I hope not too much) about the weakness of cannon 
made in one mass. It remains for me to record what has been done to 
prove practically the advantage of making them of concentric lamin. 
In February, 1855, I made an 18-pounder cannon of a cast-iron 
gas-pipe, with two layers of wrought-iron hoops shrunk on it. It was 
so strong that I afterwards had it bored out to the diameter of a 24- 
R. I, A. PROC.—VOL. VII. 22 
