1 8 LEADING AMERICAN MEN OF SCIENCE 



foundation of the science of interior ballistics by an attempt to 

 measure the explosive force of the gases produced by the explo- 

 sion of gunpowder, inventing a machine which has ever since 

 been known as "the Rumford Apparatus." This consisted of a 

 small steel mortar mounted vertically upon a bed of solid masonry. 

 The J inch bore was closed by a steel hemisphere upon which 

 weights were placed and these increased until they were no longer 

 lifted by the force of the gunpowder exploded. To avoid loss of 

 energy by the escape of gases through the vent, the powder was 

 ignited by applying a red-hot iron ball to the lower end. He 

 gradually increased the charge of powder, until an 8,000 pound 

 cannon had to be used as a weight to counterbalance the force of 

 the explosion, and then the barrel of the apparatus burst into 

 halves. His numerical results were too high, but it was almost a 

 century before better figures were obtained. 



Rumford's earlier experiments in England were mostly directed 

 to the problems of external ballistics, especially to the determina- 

 tion of the velocity of the projectile under different charges and 

 kinds of powders and methods of firing. For this purpose he first 

 made use of the ballistic pendulum invented by Robins. The 

 bullet was fired into a wooden target backed with iron and sus- 

 pended so as to swing back freely when struck. By measuring 

 the chord of the arc of its swing and knowing its weight and that 

 of the bullet, the velocity of the bullet could be calculated. 



Rumford improved upon this by measuring the momentum of 

 the gun as well as the equal momentum of the bullet by suspend- 

 ing the gun itself as a pendulum by two cords. This not only 

 gave another series of figures as a check to the former, but it was 

 more accurate, because the movement of a large mass at low 

 velocity can be more easily measured than of a small mass at high 

 velocity. 



In his later experiments in Munich he discarded the pendulum 

 target and measured the velocity of the ball solely by the recoil 

 of the gun, experimenting with brass cannon as large as twelve- 

 pounders, in a building which he had erected for the purpose. 

 He was never content with laboratory experiments, and to con- 



