O. N. Rood on Elongated Projectiles. 25 
base of the ball could be so shaped that in its passage through 
the air this vacuum might in great part be prevented by air 
rushing in at a certain, but lower rate than 1150 feet. It is 
evident that the lower this rate is made, the more do we sub- 
tract from the pressure in front, that is, diminish the resistance 
to the flight. 
Suppose the base constructed like 6. 
ed, Fig. 6,and the velocity of trans- « b 
lation 1100 feet per second, then it 
is evident that while ab is the mea- 
feet, ac will be the measure of the 
velocity with which the air must 
rush in to prevent a vacuum, and bd = ed 
by construction ac is only 635 feet. eh tee 
We should be led to expect that a projectile of this sha 
would experience less resistance than one provided with a flat 
base, until the velocity of translation was increased so that ac 
ecame equal to 1150 feet, which in the model used by me takes 
place of course when aé or the velocity of translation is 1992 feet 
persecond. Every effort was made to give these double cones as 
great a length as possible; many models were tried, and the 
length was slowly diminished until the new projectiles flew tru- 
y; finally, moulds for two balls of this model ". 
were perfected for rifles No.2 and No. 4, 
and atter some slight alterations the new 
double cones rivaled in accuracy of perform- 
ance the pickets with flat bases. To accom- 
plish this, it was found necessary to cut the 
patch as seen in Fig. 7, which ensured accu- 
rate ine | 
elow are the results of a number of ex- | 
periments on the time of flight of the old flat- eee eee 
ended balls and of the new double cones, together’ with their 
average velocities from 110 to 500 yards. 
Single Cones. (Weight 113°34 grains.) 
Rifle No. 4. Initial Velocity 1128 ft. 
Distance,. Time of Flight. Average Velocity. 
110 yards, é 993 feet. 
ig 6947 “ 950. “ 
500 « 1885 .:” 795. »," 
Double Cones. (Weight 109 grains.) 
Rifle No. 4. Initial Velocity 1138 ft. 
Distance, Time of Flight. Average Velocity. 
110 yards, +32795 sec 1006 feet, 
* "71725" “ “ 
rd 
500 T9 2-05680 “ce 729 “ 
SECOND SERIES, Vor. XXX, No. 88.—JULY, 1860. 
4 
