Big Guns. 127 



BIG GUNS. 



By Col. J. W. Abert. 



(Read November. 1888.) 



The advances in artillery since our late war have placed gunnery 

 among the most refined mechanical sciences of the age. 



In 1842 experiments were made by Col. Bomford U. S. A., 

 which showed the diminishing pressure of a charge of powder from 

 the breech to the muzzle of a cannon. These experiments con- 

 trolled the external form of the gun. And the tensile strength of 

 a square inch bar, of the metal of which the gun was composed, 

 showed its strength, and limited the quantity of powder in the 

 <:hnrge. 



When we consider that 200 pounds to the square inch is the limit 

 of the test of our steamboat boilers, and that some of our steel guns 

 are made of metal which possessed a tensile strength of 33 tons to 

 the square inch, we can appreciate the stupendious power of the 

 machines which the progress in the art of war has placed in our 

 hands in the rifled cannon of the present times. 



It is an axiom in artillery that no gun can sustain a pressure per 

 square inch greater than the tensile strength of a square inch bar 

 of metal of which it is composed. 



The amount of pressure exercised by the firing of the charge of 

 powder can be shown for every part of the gun, from breech to 

 muzzle — 



First, by Bomford and Wade's experiments. 



Second, by Rodman's pressure guage. 



Third, by the Electro-ballistic Chronoscope. — 



To Prof. Joseph Henry, of the Smilhsonion Institution, and for- 

 merly my old Professor at Princeton College, N. J., belongs the 

 credit of using the electric spark in recording the velocity of pro- 

 jectiles, and solving the most difficult of problems in gunnery. 

 Thus, we obtain the initial velocity; also the velocity of the projec- 

 tiles at any point of the trajectory. 



Prof. Henry devised the first complete Electro-ballistic Chrono- 

 scope, for recording by electrical agency the time occupied by a 



