NATURAL PHILOSOPHY. 131 



where the range is comparatively short and the velocities great, the 

 difference in the result of the taper and non-taper rear is not so 

 marked as at the higher elevations, where the mean velocities of the 

 projectiles are reduced. But at all ranges the superiority exists both 

 in precision and velocity, as the elongated projectile, at no practical 

 range, has a mean velocity so great as to prevent the atmosphere 

 closing in behind it. One of the most important advantages attending 

 the use of the taper rear is, that it gives a lower trajectory, which ren- 

 ders errors in judging distance of minor importance, as the projectile 

 which skims along near the ground is more likely to hit a mark, espe- 

 cially a moving one, than a projectile which, moving in a more curved 

 path, has to drop, as it were, upon the object aimed at, whose distance 

 therefore must be accurately guessed. The taper shape of the rear 

 is peculiarly well adapted for the proper lubrication of the gun, which 

 is most essential for good shooting. 



Various forms of elongated Wliitworth projectiles, suited for special 

 purposes, were described : tubular projectiles for cutting cores out of 

 soft materials, as the sides of timber ships ; flat-fronted, hardened pro- 

 jectiles, first used by Whitworth, and afterwards by Armstrong, for 

 penetrating iron plates. It is found that these projectiles penetrate, 

 when fixed point blank, through iron plates inclined at an angle of fifty- 

 seven and a half degrees to the perpendicular. The edge of the flat 

 front, though slightly rounded, takes a hold, as it were, as soon as it 

 touches the plate, and the resistance met is merely that due to the 

 thickness of plate, measured diagonally. Official experimental trials 

 made on board the Excellent at Portsmouth showed that these projec- 

 tiles penetrate readily through water, and would go through a ship's 

 side below water-mark. 



THE MOTION OF CAMPHOR UPOX WATER. 



Mr. Charles Tomlinson has recently presented to the Royal Society, 

 London, a description of some very elaborate experiments made by 

 him in explanation of the motions of small portions of camphor when 

 thrown upon the surface of pure water. The following is an abstract 

 of the conclusions he had deduced from his investigations : That to 

 succeed in the production of these movements the camphor must be 

 thrown on the surface of clean water, in a perfectly clean vessel. 

 That these phenomena may be also produced by certain salts, and 

 other substances that diffuse readily over the surface of water. Thus 

 the motions of camphor may be imitated by placing on water floating 

 rafts of talc, tinfoil, paper, etc., smeared with or containing volatile 

 oils, or any volatile liquid, such as ether, alcohol, chloroform, etc., pro- 

 vided there be a communication between such a liquid and the water. 

 The camphor or other volatile substance, being slightly soluble in 

 water, spreads a film over the surface of the water the moment that 

 it conies in contact with it. The dimensions and form of this film evi- 

 dently depend on those of the piece of camphor operated on, and in 

 general the film separates more easily from broken surfaces and 

 angles than from a smooth surface, as the broken surface of a crystal 

 is more soluble than the natural surface. These films being con- 

 stantly detached from the camphor so long as it is in contact with the 



