THE SPHAEROBOLUS GUN 339 



to gravity, and t the time of rise or fall in seconds, neglecting the 

 resistance of the air it can be calculated that, when a sphere is shot 

 vertically upwards from rest to a height of 14-5 feet or falls to the 

 ground from that height, the time required for each movement is 

 approximately 0- 95 second. Taking into account the resistance of 

 the air, we may conclude that a projectile of Sphaerobolus which is 

 shot 14-5 feet vertically upwards doubtless takes upwards of one 

 second to reach its highest point and upwards of one second to fall 

 from the highest point back to earth again, or upwards of two 

 seconds for the double journey. 



Similarly, it can be calculated that, neglecting the resistance of 

 the air, when a sphere is shot vertically upwards to a height of 7 feet 

 instead of 14-5 feet or falls 7 feet instead of 14-5 feet, the time 

 required to carry out the movement is approximately 0- 65 second. 

 Taking into account the resistance of the air, however, we are 

 justified in concluding that the actual time for the upward or 

 downward journey would exceed 0-65 second. If we assume the 

 actual time to be 0- 75 second, then the projectile after discharge 

 and before striking the earth would be in the air for about 1 • 5 

 seconds. 



(3) Time taken in the discharge of the gun. Just before the 

 discharge of a Sphaerobolus gun, the dual everting membrane can 

 be seen to have a cup -like form and the glebal mass can be seen 

 resting within it ; and immediately after the discharge the everting 

 membrane can be seen everted and forming a pearly balloon -like 

 covering to the top of the fruit-body ; but during discharge the eye 

 cannot perceive any movement either of the everting membrane or 

 of the projectile, i.e. one does not perceive the actual discharge of 

 the gun. The reason why the eye cannot perceive the discharge 

 of the Sphaerobolus gun is that the movements of the everting 

 membrane and of the projectile are too rapid for the eye to follow. 



The time taken for the eversion of the inner dual membrane of 

 the Sphaerobolus gun can be readily calculated. Let us assume 

 that the projectile has been shot to the maximum observed height 

 of 14-5 feet. From a calculation already made we know that the 

 initial velocity of the projectile, as this leaves the everting mem- 

 brane, is about 30 feet per second. Since this velocity is due to the 



