406 



TRANSACTIONS OF THE AMERICAN INSTITUTE. 



colder. The outward pressure of the powder at the time of this fracture 

 would surely have carried away so thin a piece of metal; but it remains 

 standing to show that the pressure against the surface had been reduced before 

 the gun broke — a remarkable evidence of the true cause of the bursting of 

 the gun. The diagram exhibiting the place and quantity of heat shows but 

 little heat at any of the surfaces of the gun. From this, also, we may have 

 been hitherto deceived as to the importance of the study of its effects; and 

 we can only appreciate it by some experiments like the following: A clean 

 rifled musket, the barrel of which weighed about five and a quarter pounds, 

 was fired twelve times with the ordinary charge, at intervals of five 

 minutes between each discharge. The time during which the surface of 

 the musket was radiating away the heat from beginning to end was, there- 

 fore, about one hour. At the end of this time its temperature was 200*^. 

 The radiation was somewhat hindered by the wood of the stock, which was 

 a non-conductor, partially enveloping the barrel, and the burnished surface 

 of the barrel, which was a non-radiator. The whole amount of powder was 

 less than one ounce, and it communicated this great amount of heat to five 

 and a half pounds of metal. There would be a material difference in the 

 amount of heat communicated in this experiment, if the barrel were not 

 clean inside, as the residuum of powder would be a non-conductor, and 

 would prevent its communication to the metal of the barrel. The tempera- 

 ture of the gases in a large gun, say 100-pounder rifled cannon, would be 

 much greater than in a musket; as the temperature is increased as the 

 resistance to the expansion of the powder is increased. The work of the 

 powder in a gun is to overcome the inertia of the shot, and to do this it 

 presses against a certain number of inches of area. If the shot be short, 

 the pressure is still exerted against the same area. The projectile in a 

 100-pounder rifle gun is about 12 inches in length, while the pi'ojectile from 

 a common rifled musket is less than one inch in length. The resistance 

 from the inertia would be thus about twelve times as great in the large 

 gun as in the small one, and the expansive force or pressure, and conse- 

 quently the temperature, high in proportion. 



The ordinary meters, if used to measure the temperature communicated 

 to the gun, as shown hy the preceding argument, will be inefficient, as they 

 cannot be applied at the place supposed to be the seat of the highest tempera- 

 ture. A meter for this purpose can be prepared in the following manner: 



M'^./7- 



Take a gun with eight inches thickness of metal about the bore, cut off 

 the chase at that point of its length where the metal is five inches in thick- 



