320 
pounder. It was then 24 inches thick at the strongest part, yet it bore 
being fired with 4lbs., 5lbs., 6 Ibs., 7 lbs., and ultimately several times 
with 8 Ibs. of powder, and a 24-pound shot. 
In May, 1855, I altered an ordinary cannon, cutting away some of 
the useless outside part, and replacing it with metal, put on with initial 
tension. This was a most satisfactory experiment, for an unaltered 
cannon of cast-iron, of the same size and weight, and one of brass, were 
tried against it. All three were fired 68 times with one charge of pow- 
der and one shot; 26 times, 14 charge, 1 shot; 5 times, 14 charge, 
1 shot; 5 times, 14 charge, 2 shots; 110 times, 2 charges, 2 shots. 
The cast-iron gun here burst at this round. Firmg was continued 
from the brass gun and mine, 74 rounds more, with double charges of 
powder and 2 shots, when the brass gun was found to have utterly lost 
its shape. After the destruction of both its rivals, 1384 rounds more 
were fired from my gun with the same charge; then double charges of 
powder, and 3, 4, and 5 shots were tried, till the barrel was filled. It 
was fired 158 times with a double charge of powder, and crammed to the 
muzzle with bullets. Although these two guns and three others were 
finished by me before Mr. Mallet read his paper here, yet I had taken 
such precautions to keep my proceedings secret (as we were engaged in 
war with Russia at the time) that it is utterly impossible he could have 
learned anything from me. 
In the spring of 1855 Mr. James Longridge, a civil engineer, noted 
for his mathematical skill, arrived at the same conclusion as Mr. Mallet, 
Dr. Hart, and myself. He put them into practice by making a 9- 
pounder gun of a thin iron tube, with wire wound round it with an 
accurately measured tension. This is, doubtless, the way to make the 
strongest possible tube from a given quantity of metal, and will, I ex- 
pect, be found of great value in the construction of monster mortars. 
Next in point of date comes the French naval rifled cannon, adopted in 
1858. It is made only in two layers, the inner of cast-iron, and in one 
piece; the outer one of wrought iron, and in five pieces. About the 
same time Colonel Cavalli commenced to make his breech-loading cannon in 
two layers also, the inner tube being of brass, but short, extending only 
round the seat of the charge, and a few inches in front of it. The rest 
of his guns are of cast-iron. In 1859 the celebrated Armstrong gun was 
adopted into the military service of this country. It, too, is built up. 
The inner layer is made by twisting bars of iron into coils, welding each 
coil into a short cylinder, and then welding those cylinders together end 
to end. The next layer is made by welding together lengthways two 
long pieces, semi-cylindrical in section; the third layer is made of coils, 
like the first, but these are not welded to each other. I should observe 
that Sir W. Armstrong disclaims most distinctly any desire to obtain 
strength by adjusting the size of the different layers, and although I 
talked over with him the theory advanced by-Mr. Mallet and myself 
some months before he brought forward his present gun, yet he learned 
nothing from My. Mallet or myself; and if he puts the tubes together 
with the requisite degree of tension, he does so by pure accident. 
