432 Mr. Mallet on the Physical Conditions 



CHAPTER XXVI. — Change of Crystalline Axis in Weohght-Ieon, Cold. 



SECTIONS. PAGE. 



219, 220 Much loosely written on the subject; three provisional conclusions from our exist- 

 ing knowledge, 256, 257 



221 Illustration of these in the familiar method of nicking, by which a blacksmith 



breaks a bar of iron cold, 258, 259 



222 The instance is but a case of the general law of crystalline arrangement, the prin- 



cipal axes assuming the directions of least pressure in the mass ; practical de- 

 ductions as to wrought-iron artillery, 259 



223-225 Mr. Hood ; Mr. Thorneycroft's papers on the subject ; the general crystalline 



law, the key to the question, 260 



CHAPTER XXVII. — Effects of the Variable Rapidity of the Blow or of 

 THE Velocity of Application of the Roptoring Strain, npoN the Character 

 OF Fracture of the same WEonoHT-lRON. 



226 Struck by cannon-shot, the most fibrous wrought-iron breaks short and crystalline ; 



experiments at Woolwich, 260, 261 



227, 228 Why should rapidity of blow alter the nature of the fracture; the relation between 

 toughness and possible rapidity of bending without fracture long known ; in- 

 stances from various bodies, 261, 262 



229, 230 Reasons assigned; Dr. Young's principles; general formula for vis viva of fracture; 



application to wrought-iron, 262, 263 



231-233 In the instances given, the fracture has the same character, whatever be the velocity 



of the production ; not so in metals (iron) ; reasons assigned, 264 



234, 235 Effects analogous to those produced in breaking a bar {see 221), and but another 

 case of the general crystalline law; Swedeuborg, Malberg, on the structure of 

 iron, 265, 266 



CHAPTER XXVIII. — The Relative Injury done by the Stroke of Shot, to 

 Guns of different Materials. 



236 Experiments made at Lafere, 266 



237 None similar fur wrought-iron ; prediction on principle, 266 



238 Steel gun in relation to mass; oast-iron, bronze, wrought-iron, 267 



CHAPTER XXIX The mutual relations of the Material of the Gun and 



OF the Rapidity of Explosion of the Charge. 



239, 240 Explosive compounds become gaseous with different degrees of rapidity; scale of, . 267 



241 Gunpowder varies in its rate of explosion with certain circumstances; effect of high 



drying and of heating it, 268 



242 E.xperlment in illustration; the distress upon the gun dependent upon the rapidity 



of explosion, 268 



243 Vis villa of the explosion of the shot, and of the recoil, 269 



244 Hutton's law, V : -j/P, verified for gun-cotton, 269 



245 Table XII. ; comparative effects of gunpowder and of gun-cotton, 269 



246 The question of distress upon the gun, resolves itself into one of maximum pressure 



per square inch, 270 



247 French experiments to determine the maximum mean pressures per square inch of 



gunpowder and of gun-cotton ; equation for the mean effect of the charge; Table 

 XIII.; velocity, vl^ viva, and mean effect due to gunpowder and gun-cotton, 130, 271 



248 Caliber ; length lor maximum effect, and maximum pressure per square inch for gun- 



powder and for gun-cotton, 27 1 



