396 



Mr. Mallet on the Physical Conditions 



and breadth of the prismatic hollow produced, and considering the hardness to be in 

 each case inversely as the volume of the material thus displaced. The results thus ob- 

 tained are, no doubt, of value ; but it admits of question whether, for artillery pur- 

 poses, the steel prism should not be impelled by the impulse of a constant weight, at a 

 constant velocity, i. e., falling from a constant height, instead of being merely slowly 

 pressed into the metal; and it is further obvious, from the remarks of the text (chaps. 27, 

 28, 29, 30), that neither method will afford any true measure of the abrasion and wear of 

 guns in service. 



The following Table is a resume of the properties of the four principal materials for 

 ordnance, collected from the American experiments, and may be usefully compared with 

 the Table siv. of the text :— 



Physical Properties of the Materials for Ordnance. 



The strongest is to the weakest cast-iron thus as 5 : 1 in direct tension ; as 2 : 1 in trans- 

 verse strain, torsion, and compression ; and as 7 : 1 in hardness. Bronze varies in tenacity 

 as 3 : 1. The Reports state that " the properties of metals, which are the most essential in 

 the manufacture of cannon, are tenacity and hardness, and, as holding an intimate relation 

 to these, density;' but it is surprising to find that nothing is said of the importance of 

 extensibility uithin the elastic limit, which, I would hope, the principles enunciated in the 

 text have sufficiently shown to be, next to cohesion itself, the most important physical con- 

 stants that relate to the materials for the construction of cannon ; one, the past neglect of 

 which has been productive of more failure, and abortive, but costly, attempts at improve- 

 ment of ordnance, than any other. 



