32 . Scientific Proceedings, Royal Dublin Society. 



experiments to determine what this is, those hitherto made with 

 ordnance being directed to the law of penetration in such substances 

 as wood, brick, sand, clay, &c. The remarkable effects produced 

 by firing rifle bullets into soft, inelastic substances, prove that the 

 resistance increases as a high power of the velocity, the penetration 

 diminishing when a certain limit of speed is exceeded. 



The relative velocities of small shot, and of the birds and 

 animals against which it is used, is beyond the scope of this Paper ; 

 but it will be seen that the time of flight of medium shot being j-th 

 of a second for 40 yards, a very large allowance must be made in 

 many instances to ensure striking: In the case of a driven bird 

 crossing at that distance at a rate ©f 60 miles an hour (a high, but 

 possible speed) , the allowance for the motion of bird should be about 

 15 feet, as it will move 12i feet in ^th of a second, and the time 

 occupied in the act of firing the gun, and the passage of the shot 

 from breech to muzzle, must be also allowed for. It will be seen, 

 therefore, how difiicult it is to attain anything like certainty in 

 stopping birds flying at high speeds across or overhead. 



Before concluding, I would direct attention to the magnitude 

 of the resistances developed in the air by high velocities. The 

 resistance to a spherical shot 15 inches in diameter, moving at a rate 

 of 2100 f. s., is ®4t31 lbs. A flat surface of equal diameter would 

 experience a higher resistance. Again, the same shot started at a 

 speed of only 1700 f. s. loses, from the resistance of the air alone, 

 in the first 100 feet of its flight, and in less than the yfo-th part of 

 a second, 76 foot tons of energy. 



It appears to follow from these facts, that whenever it is sought 

 to obtain motion by using the resistance of the air, the efforts of 

 inventors should be directed to giving a maximum speed to their 

 machines, rather than an extended surface. It is probable that if 

 the problem of driving serial machines be ever practically solved, it 

 will be by attaining high speed in the propellers, and thus utilizing 

 the enormous resistance which the air offers to bodies moving 

 through it at high velocities. 



