346 
THE 80-TON GUN. 
The now well-known principle of shrinking on the successive layers 
affords very great additional strength to the system, since by its aid 
the strain of the discharge is transmitted to the very exterior of the 
gun, which thus adds its quota to the resistance. The efficacy of the 
shrinking process is well shown by the measurements taken of the 
interior of the gun during manufacture. Thus the shrinkage of the 
powerful coiled breech-piece caused the bore to contract ‘020 in., and 
the compression of the massive outer coil carrying the trunnions was 
so great that it was transmitted through the breech-piece, and caused 
a further contraction of ’023 in. in the bore. 
The shrinkage was so adjusted that the maximum contraction 
(•043 in.) took place at a point 32 ins. from the end of the bore, and 
gradually died away in each direction towards breech and muzzle. 
Thus the pressure of the gas—which is greatest in the powder-chamber 
and for a short distance in front of the base of the shot—was directly 
transmitted to the outer or C coil, the great strength and thickness of 
which form an important point in the system. It often happens, on 
firing a new gun, that the shock of discharge permits the atoms of the 
material to shake themselves, as it were, and to settle down more com¬ 
fortably. This sometimes results in the shrinkage of the outer coils 
taking increased effect on the steel tube; but more usually the steel 
tube fits its exterior better to the interior of the coils, or perhaps 
slightly compresses their nearest particles, so that a small expansion 
ensues. Before enumerating and describing the experiments made 
with the 80-ton gun, it will be convenient to finish this part of the 
subject, and to draw attention to the table (B) of measurements here 
given. The figures represent the diameter of the bore at short 
TABLE B. 
Showing Horizontal Measurements of the Bore of the 80 -ton Gun. 
Inches from 
muzzle. 
Before 
shrinking on 
outer coil. 
After 
shrinking on 
outer coil. 
After firing 
21 rounds. 
ins. 
ins. 
ins. 
ins. 
190 . 
14-498 
14-498 
14-498 
196 . 
14-498 
14-498 
14-498 
Contraction. 
202 . 
14-498 
14-495 
14-494 
•001 
208 . 
14-498 
14-494 
14-493 
•001 
214 . 
14-499 
14-495 
14-494 
•001 
220 . 
14-499 
14-494 
14-492 
•002 
226 . 
14-499 
14-490 
14-490 
Nil. 
Expansion. 
232 . 
14500 
14-488 
14-489 
•001 
238 . 
14-500 
14-482 
14-484 
•002 
244 .. 
14-499 
14-480 
14-481 
•001 
260 . 
14-499 
14-476 
14-480 
•004 
256 . 
14-499 
14-476 
14-478 
•002 
262 . 
14-500 
14-480 
14-481 
•001 
268 . 
14-500 
14-483 
14-484 
•001 
274 . 
14-495 
14-481 
14-481 
Nil. 
Note.-—T he vertical measurements are almost identical with those given above. 
intervals, taken horizontally, before and after the shrinking on of the 
outer or C coil. To the compression given must be added that of the 
