212 Captain Noble on the Pressure required to 



Then, from the definition of the parabolic twist, 



dy 



-t% = constant = c, suppose ; 



and 



But, from (21), 



Tz= cz '> 



(21) 

 (22) 



tan 2 = cz d , and tan i = cz } ; 



c — 



tan O — tan 0, 



= •047925. 



Comparing (22) with the form of this equation given in (4), 



2 

 z' 2 =kr<f), we have y ! =rcj) and k= — =417*3. 



c 



Hence the equation to the development of the parabolic rifling 



is 



s fi =417-3r<k 



(23) 



and z x the distance of the origin from the commencement of the 



rifling = l =6*555 feet. 



c 



25. As in the last case, I place in the form of a Table the results 

 given by (15) for different values of z. The values of the con- 

 stants are, r = *417 feet, £ = 417*3, p = -312 feet, ^ = '167, 

 M = -00555. 



Table showing the pressure on the studs in a 10-mcA British-service 

 gun rifled with a parabolic twist commencing at one turn in 100 

 calibres and terminating at one turn in 40 calibres, calculated from 

 (15). 



Value of z, the 

 distance from 

 the origin, in 

 feet. 



Corresponding 



travel of the shot 



in the bore, in 



feet. 



Corresponding 



velocity of shot, 



in feet. 



Total pressure 



on base of shot, 



in tons. 



Value of R, 



or total 

 pressure on 

 studs, in tons. 



6-555 



000 















6-888 



0-333 



411 



1547 



31-2 



7-500 



0-945 



675 



1077 



28-7 



8-389 



1-834 



873 



781 



290 



9-278 



2723 



992 



621 



30-2 



10-167 



3-612 



1078 



510 



31-4 



11055 



4-500 



1146 



424 



32-3 



U-944 



5-389 



1200 



356 



330 



12-833 



6-278 



1245 



305 



33-8 



13-722 



7-167 



1282 



268 



34-5 



14-610 



8055 



1311 



240 



35-2 



15-499 



8-944 



1333 



220 



35-8 



16-388 



9-833 



1349 



205 



36-3 



