Mr. Longridge on the Resistance of the Air to Projectiles. 305 



jectile an equation was found which agreed tolerably well with the 

 experimental results. 



The form of the equation assumed was 

 (x-\-a) v n =C ; 

 and the resulting equation was for the small shot 

 0+665) ^=l g-i 10-1473853, 

 and for the large shot 



O+2032)« 3 =log- 1 12-6696158, 

 the maximum error being about 1| per cent, of the velocity. 



Introducing into these equations the diameter and weight of the 

 respective projectiles, and taking the index rc = 2'5, the values of 

 C were found to be, 



W 



small shot, 

 large shot, 



C=log- 1 10-7295585 



C = log _1 10-7454405 j 2 , 

 W 



the mean being C=log _1 107375745 

 and the resulting general equation 



(^ 1Og " ll0 ; 3 v l! 745 - W ) ^=^- 1 10-7375745. 



The maximum error in velocity, as calculated by this formula, was 

 for the small shot lg per cent., and for the large shot 2\ per cent. 



From the above equation the resistance per square inch of sectional 

 area is found, 



T>_ ° 



log- 1 13-0154756' 

 from which the following Table is constructed, the third column 

 showing the resistance, as calculated by Hutton's formula: — 



Table of Resistances to a Rifled Projectile. 



Velocity, 



Resistance, in 



Hutton, 



Velocity, 



., stance, in 





feet per 



lbs., per square 



p. 218. 



feet per 



1 per square 



p. 218. 



second. 



inch. 



second. 



inch. 



1500 



18-89 



18-94 



700 



0-613 



3-12 



1400 



1387 



16-23 



600 



0-306 



2-20 



1300 



9-94 



13-67 



500 



0-135 



1-49 



1200 



6-92 



11-29 



400 



0*0494 



0-93 



1100 



3-722 



9-14 



300 



0-01354 



0-52 



1000 



3-052 



7*24 



200 



0-00218 



0-23 



900 



1-900 



5-61 



100 



0-0000965 



0-556 



800 



1-118 



4-24 









It is next shown that the hypothesis of the great increase of re- 

 sistance at velocities exceeding 1100 feet per second being due to 

 the vacuum behind the projectile is untenable, because the actual 



