342 RESEARCHES ON FUNGI 



The air which suddenly enters the cavity through the tooth-sinus 

 apertures as the inner peridial membrane becomes everted must 

 be equal in volume to the enlargement of the cavity, i.e. roughly 

 4-6 cubic mm. 



(5) Momentum of the projectile when leaving the gun. If 

 momentum be expressed by M, mass by m, and velocity by v, all 

 in corresponding units, we can write : 



M = mv. 



Let us calculate the momentum of a Sphaerobolus projectile which 

 has been shot to a maximum height of 14-5 feet. We know that 

 the projectile's initial velocity is 30 feet per second. Let us assume 

 that the projectile's radius was 0- 625 mm. and its density was 1-25 

 (the projectiles sink in water). Since 



mass = volume x density 

 and, for a sphere, 



volume = - nr z 

 3 



where r is the radius of the sphere, we have 



mass = - 7rr 3 x density 



and, where M = momentum, we have 



4 



M = - nr* x density x velocity. 



The number of cubic mm. in one cubic foot = (305) 3 = 28,000,000. 

 Hence for our projectile : 



4 2 9 0- 6 C> 5 3 1 



volume = - x — x = - cubic feet approximately. 



3 7 28,000,000 28,000,000 



The weight of one cubic foot of water is 62 lbs. Hence for our 

 projectile : 



1-25 62 „„ B ,. , , 



density = x — =77-5 pounds per cubic loot. 



The initial velocity of our projectile is known to be 30 feet per 

 second. Hence, for our projectile, with the mass expressed in 

 pounds and the velocity in feet per second, we have : 



