100 ANNUAL OF SCIENTIFIC DISCOVERY. 



The principle in all rifled cannon appears to have been to allow as 

 little windage as possible, and to make the shot fit the grooves of the 

 piece, taking from them a rotation in its flight. Mr. Mackay, on the 

 other hand, has conceived the plan of having the grooves so arranged 

 that, while the shot fits closely to their outer edge, the grooves are 

 left open for windage. By this arrangement the gas has to travel 

 some feet farther than the shot, and in doing this imparts a rapid and 

 perfect "spin" to it. The shot are of cylindrical form, perfectly 

 smooth, with conical heads, and cupped at the other end in propor- 

 tion, so that each shot is perfectly balanced from the center of its 

 length. Mr. Mackay in his patent also claims a peculiarity in the 

 wadding, which is of sawdust, by which at the movement of the first 

 ignition of the powder the elasticity of the wadding moves forward 

 the shot slightly; the effect is that the whole of the powder is burnt, 

 and the shock on the breech of the gun coasiderably lessened. Mr. 

 Mackay has had a gun made upon this principle by the Mersey Steel 

 and Iron Works Co. It is of wrought iron, weighs nine tons, has a 

 bore of 8* 12 inches, and in other respects corresponds with the gen- 

 eral features of the ordinary 68-pounder. There are 12 grooves, and, 

 as the shot do not enter these grooves, it allows of a much sharper 

 twist than in ordinary rifled guns. The velocity has been found to 

 be 1,640 feet a second. 



The following trial has been made with this gun, against a section 

 of a new iron-plated vessel, the Aj'n^ourf, now building by Laird & 

 Co. for the British Government. The target consisted of an outer 

 plate seven feet square and 5 4- inches thick, of rolled iron ; next 

 came nine inches of teak, then an inner plate or skin | of an inch 

 thick, then angle-iron and ribbing, and finally a backing up with 

 timber balks and supports 18 inches thick. The plates were 

 stated on competent authority to be the best that can be made of 

 rolled iron. The gun was charged with ;.>;) pounds of powder and a 

 cast-steel shot, weighing 107 pounds. The range was 20 ) yards. 

 The shot stru-k the target with a dull thud, a little below the bull's 

 eye on the right, and in the very strongest part, where it was backed 

 up by the rib of the ship's side, the angle-iron, and the timber balk. 

 At the point of impact a perfectly circular hole was cut. The shot 

 then powdered the teak, passed through the inner skin and the angle- 

 iron, shattered the timber balk into fragments, and was picked up 82 

 yards beyond the target, together with a circular piece of the iron 

 armor, about 80 pounds' weight, it had carried with it through the 

 back supports. The sand showed that it had spun to the last. About 

 70 fragar-nts of iron, bolts, and fragments of the inner skin and a i- 

 gle-iron were picked up 100 yards from the target. The shot when 

 found was reduced from lo inches to 11 inches in length, and in- 

 creased about 1 inch in diameter at the end which struck (lie 

 target. The other end was uninjured. The whole target was 

 forced back about six inches, and so much deranged that more shots 

 wrc not fired. 



The. Percussion of S/iof <>n frnn T<trii<'fs. The visitor at the s 'eue 

 of the experiments at Shoeburyness, in noticing the effect of the 

 shot on the tremendous targets representing sections of the War- 

 rior, the Gloire, and other frigates, cannot fail to observe that at 



