Skips, c5r. against Cannon Balls. 4-11 



the action of its curved surface in sliding, would tend to force 

 the centre of the ball out of the indentation in the same man- 

 ner, as it is easy to be perceived that the centre would de- 

 scribe the same curve if it were to roll or to slide. 



It is moreover evident that this power of turning the ball 

 from its direction would be added to that dei'ived immediately 

 from the obliquity of the side, though this would be the cause 

 of it all ; or, in other words, the effect would be different (what- 

 ever was the hardness of the side) from what it would be if 

 the ball were a mere point or flat body acting against another 

 flat oblique surface or indentation. 



Case 3. If the force should be so great that the ball en- 

 tirely buried itself, there would even then be two circumstances 

 in favour of this construction ; first, that the ball would have 

 to perforate through a greater substance than if the side were 

 perpendicular to the motion, the distance of which is shown 

 at HE, fig. 1, and the oblique distance shown at HO; and 

 secondly, because the change of motion which would take 

 place before the ball was quite buried (as above described) 

 would still further increase the length of substance to be per- 

 forated by it, and the course of the ball might be so much 

 changed that it should (after it was quite sunk) have to per- 

 forate the side through the remainder of its length upwards, 

 instead of through its direct thickness. 



It would be possible, however, for the balls to come in a 

 perpendicular direction to the side, and to go through it di- 

 recdy ; but it is improbable that this should frequently be the 

 case, and it seems that it would be less likely to happen if it 

 were fired at from a short distance than from a great one, as 

 then only a moderate elevation would be required ; whereas, 

 when the distance was small, the elevation of the guns would 

 become so great that it would be extremely difficult to take 

 an aim so that the balls should come down upon it. 



It remains to be observed, that neither of the cases would 

 exist altogether as described ; but as all substances possess a 

 certain degree of hardness and elasticity, there would be a 

 mixed effect produced, though I do not conceive the elasticity 

 of wood to be sufficiently great to alter the cases materially : 

 the results would therefore, it appears, be nearly as stated 

 when the elasticity was not supposed to exist, but with some 

 very sensible difference. 



I have also to add, that since having made the pi-eceding 

 observations, I tried the experiments relative to them on a 

 small scale, and found them precisely according to my ideas. 

 The side, fig. 1, was represented by a deal board, 3-8ths of an 

 inch tliick ; the return part W was of plate-iron, and the 

 3 F 2 inside 



