1872.] Engineering. 263 
ENGINEERING—CIVIL AND, MECHANICAL. 
Guns.—In our last quarter’s chronicles reference was made to a crack which 
had been discovered in the lining of the new 35-ton gun known as the 
‘* Woolwich Infant.” Three theories have been advanced to account for this 
internal injury, which were recently stated by Capt. Dawson, R.N., in a leGture 
on Guns, at Plymouth. The first theory is, that the bottom stud, flattened by 
the blow above the shot caused by the escaping gas, overrode the groove, 
causing a squeeze which delayed its exit, and led to an accumulation of gas 
in the powder-chamber. 2nd. That the wabble caused by balancing the shot 
on two studs, and the irregular action of the powder above it, due to the non- 
centreing of the shot, wrenched out or sheered off the stud, and set up a 
motion of the shot across the bore, which enhanced the difficulty of its escape. 
3rd. That pebble powder developed some new quality, when ignited in 120-lb. 
charges, which it did not possess when fired in quantities of 100 lbs. and 
under. Captain Dawson is evidently of opinion that the Woolwich system of 
rifling is one of the primary defects in this new gun, and that the injuries were 
attributable to the vicious system. of grooving on an increasing twist, which 
necessitated the concentration of rotary effort on a single row of studs inca- 
pable of giving adequate rotation with the present amount of spiral, and this 
angle of spiral could not be increased, because the studs would not endure the 
extra effort, but would be sheered off, and cease to aé at all. Contrasting 
other long iron bearing systems which had undergone official trial with the 
present short bearings, Capt. Dawson showed that, whilst the whole effort of 
rotating a 700-lb. shell was now thrown upon a total of 54 inches of stud 
bearing, it would under the Scott iron flange system be diffused over 13 feet 
of bearing; and that this latter system had narrower shallower grooves, which 
took only one-fourth the quantity of metal out of the gun, and therefore made 
less space for escaping gases to erode the bore; whilst, instead of the lower 
groove being spiked by its own stud, Scott’s iron flange would receive the 
shock on a rib 22} inches long. Inthe trial between two 7}-ton guns on this 
system, the Woolwich rifled gun was declared incapable of further firing, 
except ‘‘ under precautions ” against bursting, whilst the grooves and lands of 
Scott’s gun were perfectly uninjured. Yet Scott’s guns gave the greatest 
hitting power at the muzzle, and projected its shot 1500 yards with 2 degrees 
of elevation, using 20 lbs. of powder, whilst the Woolwich one required 25 lbs. 
to reach the same distance. Comparing the work done by the respective 
projectiles, the Scott iron bearing r1o-lb. shot escaped from its charge so much 
more easily than its studded rival, that—though the conditions were exadly 
alike in all else—the Scott hit a muzzle blow 133 foot-tons heavier than the 
French projectile, and no less than 260 foot-tons more powerful than that of 
the present 7-inch gun, the charges of which have to be reduced to make 
amends for its lack of endurance. 
Navigable Balloon.—The experimental balloon recently constructed by the 
French Government, upon M. Dupuy de Lome’s system, rose from the court- 
yard of the Fort Neuf, at Vincennes, on the 2nd of February last, having on 
board MM. Dupuy de Lome, Lédé (Engineer in the Marine), Yon, and Dartois 
(aérostats), and ten other persons, forming altogether a total of fourteen men. 
The construction of this aérial machine starts with the principle that, in order 
to obtain a navigable balloon, its permanence of form must be maintained 
without any sensible undulation of surface, and a horizontal axis of least 
resistance must be obtained in a direction parallel to the propelling force. 
The permanence of form is assured by a fan carried in the car, and put in 
communication by a tube, with a small balloon placed within the large one at 
its lowest part. The volume of this small balloon is one-tenth of that of the 
large one. It is furnished with a valve opening both within and without, and 
regulated by springs. The large balloon is provided with two hanging tubes 
open to the air, and falling for a distance of 25 feet from the lower part of the 
balloon. The inflation of the little balloon causes the hydrogen to fall more 
or less in the hanging tubes, but never sufficiently to force it out of their open 
ends. To obtain a horizontal plane of least resistance, the form given to the 
