THE KOYAL ARTILLERY INSTITUTION. 
153 
coil, we have two thinner coils. Thus, very much strength is gained 
by the second shrinkage, as shown by a comparison of Fig. 5 with 
Fig. 4. There is much less risk from overheating, and from second 
heating; for the inner coil is thinner, and not joined on to the coil in 
front. The outer coil is still heated a second time; but not being 
thick, and, besides, being outside, the danger is not so great. There is 
a slight disproportion in the increasing thickness of the coils, as shown 
in the diagram. The first might be slightly thinner with advantage, if 
circumferential strength only be considered, but this might detract 
from the longitudinal strength. 
Captain Stoney, R.A., Assistant-Superintendent Royal Gun Factories, 
appears to be aware of the risk run, for he says in Yol. YI. page 411, of 
the “ Proceedings of the Royal Artillery Institution : ”— 
“ With respect to the precise pattern for future construction, it would perhaps 
have been the safest course to have continued firing No. 332 gun (of the pattern 
under consideration), and then if it did not blow its breech off (its tube being so 
thin), or burst explosively without giving ample warning, to adopt it as the pattern 
for all the heavier natures. The authorities, however, have decided on constructing 
7-inch and 8-inch guns as before, on the No. 368 type (the pattern with triple 
coil), but to make 9-inch guns and upwards on the 332 type.” 
Thus the principle is recognised that the heavier the gun, the greater 
the necessity for coming to true scientific principles of construction; 
for as the size of the gun increases, our power is tested to confine and 
restrain the enormous pressure which is called into play. With the 
heaviest gun no fault can be tolerated. Though I admit that the Fraser 
gun is well suited for 9-inch guns, and guns even much bigger may be 
made on this principle, especially if the pressure of the gunpowder be 
reduced, yet I do not believe that it is capable of supplying the heaviest 
gun that can be made. It may stand up to a 1000-pr., but I am doubtful 
of its being able to exceed this, for the following reasons. 
From Captain Stoney^s remarks it may be inferred that, on account 
of the longitudinal strain, it will not be safe to reduce the proportion 
of thickness of the first coil. It will be necessary rather to increase it; 
for the pressure of the gunpowder on each square inch of the base of 
the shot must of necessity increase, on account of the column of metal 
in front of each square inch of base increasing in length. With the 
1000 -pr., therefore, the actual thickness of this coil will be at least 
equal to that of the triple coil, which failed in the 9-inch gun. The 
proportion of power gained will thus be reduced. The danger, too, 
of Dr. Percy's law of crystallisation coming into play will increase. 
External compression will manifest itself, and the tendency to split into 
two cylinders. 
4. Palliser Guns. 
These guns will never be able to compete as heavy guns, but they 
afford a wonderfully practical illustration of the value of the laws I have 
noticed. Instead of having the outside contracted on the inside, the 
inside is expanded on the outside, and this can be done by using 
