MECHANICS AND USEFUL ARTS. 85 



per cent, against four. In addition to their use in ordinary field service, 

 these machines, mounted upon a pivot instead of the wheels, may be em- 

 ployed with great effect in boat service, as an armament for ships' tops, 

 martello towers, or other works of defence. 



IMPROVEMENTS IN RIFLES. 



Mr. Whitworth, of England, in pursuing a course of experiments with a 

 view of improving the rifle, has adopted a polygonal spiral bore of a uniform 

 pitch, but more rapid than could be attained by grooves. This bore has 

 enabled him to surpass the range and penetration of the Enfield rifle ; and 

 the strain of the projectile being distributed evenly over every side of the 

 polygon, iron can be substituted for lead in the projectile. Moreover, Mr. 

 Whitworth has discovered, in the course of his experiments, that according 

 to the quickness of the turn in the polygon is the length of the projectile 

 that may be fired, so that twenty-four pound and forty-eight pound shot 

 have been sent to extraordinary ranges with half the usual charge of powder 

 from an ordinary twelve pounder howitzer. 



MALLET'S THIRTY-SIX INCH MORTARS, AND SHELLS. 



At a meeting of the British Association for 1857, Mr. Robert Mallet pre- 

 sented an abstract of a plan he had proposed to the British Government for 

 the employment of shells of a magnitude never before imagined by any 

 one, viz., of a yard in diameter, and weighing, when in flight, about a ton 

 and a quarter, and for the construction of mortars capable of projecting 

 these enormous globes. (See Annual of Scientific Discovery, 1858, page 87.) 

 Since the above-mentioned date, a colossal mortar, constructed on Mr. Mal- 

 let's plan, has been practically tested by the English Board of Ordnance, on 

 Woolwich Marshes, with charges (of projection) gradually increasing up to 

 seventy pounds. With this amount of powder, a shell weighing 2550 pounds 

 was thrown a horizontal range of upwards of a mile and a half to the height 

 of probably three-quarters of a mile, and, falling, penetrated the compact 

 and then hard, dry earth of the Woolwich range to a depth of more than 

 eighteen feet, throwing about cartloads of earth and stones by the mere 

 splash of the fall of the empty shell. 



The explosive power, it is obvious, is approximately proportionate to the 

 weight of powder; but, by calculations, of which the result only can here 

 be given, Mr. Mallet has shown that the total power of demolition, that is to 

 say, the absolute amount of damage done in throwing down buildings, 

 walls, etc., by one 36-inch shell, is sixteen hundred times that possible to be 

 done by one 13-inch shell; and that an object which a 13-inch shell could 

 just overturn at one yard from its centre, will be overthrown by the 36-inch 

 shell at forty yards' distance. 



No bomb-proof arch (so-called) now exists in Europe capable of resisting 

 the fall of one of those huge shells upon it, whose energy of descent may 

 be represented as equal to about eight hundred tons. No means or precau- 

 tions are possible in a fortress against the tremendous fall of such masses, 

 still more against the terrible powers of their explosion, when 480 pounds of 

 powder, fired to the very best advantage, puts in motion the fragments of 

 more than a ton of iron, no splinter proof, no ordinary vaulting, perhaps no 

 casemate exists capable of resisting their fall and explosion, either of which 



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