PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 419 



inner metal of the gun that would prevent fracture; and, undoubtedly, if it 

 ever occurred to an ordnance officer to inquire whether the communication 

 of heat to the inner metal of guns was the cause of their failure, the 

 beginning of fracture on the inside would appear to him an argument against 

 the theory. This I consider a critical point, but one 

 directly favoring my theory. It repuires a most familiar 

 knowledge of the effects of heat, and a careful recollec- 

 tion of time and place of all the phenomena, to compre- 

 liend and explain this part of the subject. The accom- 

 pan3nng diagram exhibits a cross section of a gnu 

 at the point of greatest pressure, and, consequently, 

 highest temperature; the surface of the bore is sup- 

 posed in this example, to be continuoudy exposed to the high temperature 

 evolved from the combustion of powder when its expansive force is resisted 

 by the inertia of a heavy projectile, or, a.s* if afire were constantly burning 

 uithin the gun. The space betiveen the curved lines represents tlie place and 

 (piantity of heat thus communicated to the metal, showing the greatest, 

 expansion immediately at the surface of the bore. 



To represent a reduction of temperature by lines converging towards each 

 other I know is unusual, but as no conventional lines have been adopted to 

 represent intensity of heat by their direction, and as I have confidence ray 

 meaning will be understood, I have chosen to use them in this manner. 



We are to recollect that, in the most rapid firing, the surface of the 

 bore is exposed to this high temperature onl}'^ about one hundredth part of 

 the time, while during the other ninety-nine hundredths the heat of the 

 surface of the bore is radiating away. If the diagram represented a gun 

 of six inches diameter of bore and eight inches thickness of metal about 

 the bore, the range to which the heat would penetrate the metal at the first 

 discharge would be about four inches; for heat enters metal with a velocity 

 depending on the difference in temperature of the source from which it 

 flows and the metal into which it is flowing. The heat is communicated 

 to the small surface of the bore, while it is radiated from the large 

 outside surface of the gun; from this cause, if from no other, the tempera- 

 ture would be much higher within the mass than on the outside. 



The penetration from the first discharge being four inches, it might be 

 supposed that the range of the heat from the next discharge would be 

 greater; but heat having been communicated by the first discharge, the 

 range of the second is less, from the reduced difference of temperature. 

 Although, of course, the heat flows onward, its motion is very slow. If, 

 then, the penetration be four inches, at the distance of four inches from the 

 surface of the bore the temperature will be comparatively low, but little 

 higher than that of the metal at four and a half inches from the surface of 

 the bore. The heat, therefore, is conducted from the point of four to that 

 of four and a half inches slowly; more slowly from that of four and a 

 half to five, and with a continually reduced and very slow rate of motion 

 to the outside. 



As the heat is communicated from one inner stratum to the stratum sur- 

 rounding it, for each inch of the increasing distance it travels, the mass of 

 which the temperature has to be raised is greater in circumference also; 



