138 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1917. 



The fragments of the ogival and base will be thrown with less 

 velocity but nevertheless they will have a velocity greater than the 

 residual velocity of the projectile. 



II. ARRANGEMENTS OF THE EXPLOSIVE PROJECTILE. 



The arrangement and proportioning of the parts of the explosive- 

 containing projectile determine the functions it is to play. It may 

 be required for the demolition and dispersion of weak defenses 

 situated close at hand, and then thin- walled projectiles carrying 

 large charges of explosives would be made use of, and as their re- 

 sistance to the effects in firing is not great they would be discharged 

 under low pressures. 



In order to augment their range and penetration they would be 

 fired at high angles near to or greater than 45°. It is advantageous 

 to use for this short caliber pieces such as obuses or mortars. 



If it is desired to produce destructive effects at great distances, 

 the weight of the projectile and consequently the caliber will be 

 increased. In case of unusually great distances, such as 20 kilometers 

 or more, quite long cannon and high initial velocities must be em- 

 ployed. These guns are fired under high pressures and it is necessary 

 to reinforce the walls of the projectiles to an equal caliber and reduce 

 the interior explosive charge. 



The considerations of a general nature relative to shell having been 

 treated of, it remains to discuss those relative to the choosing of the 

 explosive and the fixing of the charge. 



1. CONDITIONS OF LOADING. 



Industrial explosives are generally used in cartridges or sticks 

 w T hich are placed in bore holes in the interior of the material tha't is 

 to be blown up. They are not, therefore, exposed to any violence. 



The explosive charge of a shell must, on the contrary, endure the 

 forces of inertia, translation, and rotation due to accelerations origi- 

 nating in the chamber of the piece. 



For the purpose of showing the magnitude of these forces we will 

 take as an example the shell of a cannon of 75. This projectile is 

 subjected during firing to a minimum acceleration of the order of 

 200,000 meters per second. Its ratio to g (acceleration due to its 

 weight) being about 20,000, it results that the particular material 

 contained in the shell develops at the moment of firing under inertia 

 an effect directed toward the base of the shell equal to about 20,000 

 times its weight. 



The height of the shell cavity occupied by the charge being on the 

 average about 20 centimeters, it follows, if we designate the specific 



