Charges of greatest Efficacy for Artillery at Sea. 327 



velocity and weight of ball jointly*. Hence, since it has 

 been determined from experiment that a charge of half a 

 pound impelled a shot weighing one pound with a velocity 

 of lo'OO feet per second ; we shall, considering V the velo- 

 city of any ball impinging on the side of the vessel, have 

 for the expression of the charge impelling it through the 

 _ $dnRv*w 



s P aceS -2Di^x^r 



Now to apply this in the present instance, it is first ne- 

 cessary that a case be known concerning the penetration 

 of a given shot into oak. Such a case is presented at 

 page 273 of Dr. Hutton's Robins's New Principles of 

 Gunnery. It is there asserted that an 18-pounder cast-iron 

 ball penetrated a block of well-seasoned oak, such as ships 

 of war are generally built with, to the depth of 2>\ inches 

 when fired with a velocity of 400 feet per second. Making, 

 therefore, this the standard of comparison for all cases where 

 the object is of oak substance, we shall have for the charge 



7 . 400* x *42 SnRw . 



generally =- x -^ — ; or, because the balls 



2xi600*x ir 



24 



are of the same specific gravity, and the substance the 



j tvt • -n u 400* X '42 

 same, or R = r, and N = ra; it will be — x 



2xi6Wx — 



— - == '045 x — ,y ; that is the charge vanes as the space 



to be penetrated and weight of ball directly, and diameter 

 of the ball inversely. 



But the charge by the question being to produce the 

 greatest effect possible in the destruction of the vessel; S 

 in the above formula must always be put equal to the given 

 thickness of its side plus the radius of the ball; since it is 

 well ascertained that, for a shot to produce the most damage 

 to any splintering object, such as oak; it must lose all its 

 motion just as it quits the superior or further surface of it. 



-ft , » . • (S-r4DW ' 



Hence the charge in question is =«045 x — . o 



being the thicknes of the side of the vessel, iu the weight 

 of the ball, and D its diameter. 



We have supposed, that the resistance opposed to the 

 ( ball's motion is uniform throughout the entire penetration; 



* This law of variation of the char -rei does not exactly obtain in practice 

 after a certain charge, on account of the definite lengths of the guns: but it 

 is presumed the deviation from it, if known, would not materially affect 

 pur re.su Its, 



X 4 which 



